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What instances are there in which two species share the same binomial name?

What instances are there in which two species share the same binomial name?


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Since binomials are required to be unique only within a kingdom, two species can share the same binomial name if they are in different kingdoms. I know of one instance of this, Orestias elegans: this name denotes a species of fish (kingdom Animalia) as well as a species of orchid (kingdom Plantae).

Are there other instances where one binomial name validly refers to two (or more!) species?


There are four other instances of species-level hemihomonyms I can find:

  1. Agathis montana can be either a critically endangered species of conifer or a parasitic insect.
  2. Centropogon australis can be either a fish or a plant with a long red flower.
  3. Asterina gibbosa can be either a sea star or a type of fungus
  4. Baileya australis can be a moth or a yellow flowering plant

In addition to the five listed above, Wikipedia currently shows two others, for a total of seven:

Ficus variegata can be either a sea snail or a fig

Tritonia pallida can be either a nudibranch or an iris

See "Hemihomonyms" here.


Animal Diversity Web

Every recognized species on earth (at least in theory) is given a two-part scientific name. This system is called "binomial nomenclature." These names are important because they allow people throughout the world to communicate unambiguously about animal species. This works because there are sets of international rules about how to name animals and zoologists try to avoid naming the same thing more than once, though this does sometimes happen. These naming rules mean that every scientific name is unique. For example, if bluegill sunfish are given the scientific name Lepomis macrochirus, no other animal species can be given the same name. So, if you are a Russian scientist studying relatives of sunfish and you want to discuss bluegill sunfish with a Canadian researcher, you both use the scientific name and know exactly what the other is talking about.

Scientific names are also designed to tell you something about the animal's relationships with other animals. The scientific name of each species is made up of a generic name (generic epithet) and a specific name (specific epithet). In our bluegill sunfish example the generic epithet is Lepomis and the specific epithet is macrochirus. The generic epithet is the name of the genus (singular of genera) to which bluegill sunfish belong, the genus Lepomis. Some genera contain only one species but most genera are made up of many species. There are other species of sunfish in the genus Lepomis, examples are Lepomis cyanellus (green sunfish), Lepomis megalotis (longear sunfish), and Lepomis gibbosus (pumpkinseed sunfish). Notice that all of these species share the same generic epithet, this indicates that they are all thought to be more closely related to each other than to any other species of fish. The genus is the first level of taxonomic organization, in a way, because all species that are thought to be most closely related, are placed together in a genus.

Scientific names are often descriptive also, suggesting something about the animal. For instance, longear sunfishes have long and conspicuous operculum flaps (a hardened structure extending from the gill flap), making them look like they have long ears. The specific name, megalotis, means "big ears." Another example is yellow-headed blackbirds, whose scientific name is Xanthocephalus xanthocephalus, which literally means "yellow-headed, yellow head." Scientific names also sometimes bear the names of people who were instrumental in discovering or describing the species. Myotis keenii, "Keen's mouse-eared bat," is named after a gentleman named Keen (Myotis means "mouse-eared"). They may also contain references to regions where the species are found, such as southern right whales, Eubalaena australis, which translates to "southern true-baleen." Finally, some scientific names reflect the common names given to these animals by native peoples, such as Oncifelis guigna, a small, South American cat species called guigna by people of Chile and Argentina.

Common names can be misleading

Unlike scientific names, common names are not unique. As a result, common name usage can lead to confusion about what animal is being referred to and what their relationships are to other animals. An example are "badgers." There are various animals worldwide that are superficially similar, honey badgers (Mellivora capensis), North American badgers (Taxidea taxus), Eurasian badgers (Meles meles), stink badgers (Mydaus javanensis), and ferret badgers (Melogale personata). Although they are all called "badgers" and they are all members of the same mammalian family, they are not each other's closest relatives.

There are many examples of confusing and redundant common names, just remember that you can't rely on the common name to tell you anything about the animal's evolutionary history.

Scientific names are sometimes changed

Taxonomy, the science and process of naming living organisms, is a field that is constantly changing. When our scientific understanding of animal species and their relationships changes, it may mean that scientific names change as well. For example, all small cat species were once included in the genus Felis. They have since been split into multiple genera in order to better represent important evolutionary differences among them. Bobcats were once known by the scientific name, Felis rufus, this name has since been changed to Lynx rufus. Unfortunately, older scientific literature on bobcats will still be found under Felis rufus and some sources may not recognize the name change right away.

Some species have come to be known by multiple scientific names. In such cases one name is chosen for the species and the other names are referred to as "synonyms" of the species name. For example, all bats in the genus Lasiurus were once also known by the generic name Nycteris. So Lasiurus borealis would have also been known as Nycteris borealis. The valid, currently recognized name is Lasiurus borealis and Nycteris borealis is considered a synonym.

If you cannot find information for a particular scientific name try searching the taxonomy databases we use, to be sure that the species isn't known by a different name.


2.1 Levels of Organization of Living Things

Living things are highly organized and structured, following a hierarchy on a scale from small to large. The atom is the smallest and most fundamental unit of matter. It consists of a nucleus, containing protons and neutrons, surrounded by electrons (Figure 2.2). Atoms form molecules. A molecule is a chemical structure consisting of at least two atoms held together by a chemical bond. Many molecules that are biologically important are biomolecules (also called macromolecules), which are large molecules that are typically formed by combining smaller units called monomers. An example of a biomolecule is deoxyribonucleic acid (DNA) (Figure 2.3), which contains the instructions for the functioning of the organism that contains it. Other important biomolecules used by living organisms besides nucleic acids include proteins, carbohydrates, and lipids.

Figure 2.2 Elements, such as helium, depicted here, are made up of atoms. Atoms are made up of protons and neutrons located within the nucleus, with electrons in orbitals surrounding the nucleus. (credit: Openstax Biology 2e)

Figure 2.3 A molecule, like this large DNA biomolecule, is composed of atoms. (credit: “Brian0918″/Wikimedia Commons). To see an animation of this DNA molecule, click here (http://openstaxcollege.org/l/rotating_DNA2) .

Some cells contain aggregates of biomolecules surrounded by membranes these are called organelles (Figure 2.4). Organelles are small structures that exist within cells and perform specialized functions (ex- mitochondria make ATP, chloroplasts make glucose by photosynthesis). All living things are made of cells the cell itself is the smallest fundamental unit of structure in living organisms. Cells have all of the properties of life, which include that they are composed of biomolecules, the ability to metabolize, composed of cells, maintain homeostasis, respond to external stimuli, grow and reproduce, and evolve. (Viruses are not considered living because they are not made of cells. To make new viruses, they have to invade and hijack a living cell only then can they obtain the materials they need to reproduce.) Some organisms consist of a single cell and others are multicellular. Cells are classified as prokaryotic or eukaryotic. Prokaryotes are single-celled organisms that lack organelles surrounded by a membrane and do not have nuclei surrounded by nuclear membranes (Figure 2.5) in contrast, the cells of eukaryotes do have membrane-bound organelles and nuclei (Figure 2.4).

a. Animal Cell

b. Plant Cell

Figure 2.4 These figures show the major organelles and other cell components of (a) a typical eukaryotic animal cell and (b) a typical eukaryotic plant cell. The plant cell has a cell wall, chloroplasts, plastids, and a central vacuole—structures not found in animal cells. Most plant cells do not have lysosomes or centrosomes. (credit: Openstax Biology 2e)

Figure 2.5 This figure shows the generalized structure of a prokaryotic cell. All prokaryotes have chromosomal DNA localized in a nucleoid, ribosomes, a cell membrane, and a cell wall. The other structures shown are present in some, but not all, bacteria. (credit: Openstax Biology 2e)

In most multicellular organisms, cells combine to make tissues, which are groups of similar cells carrying out the same function (ex- muscle tissue, nervous tissue, epithelial tissue, connective tissue). Organs are collections of two or more tissue types grouped together based on a common function. Organs are present not only in animals but also in plants. An organ system is a higher level of organization that consists of functionally related organs. For example vertebrate animals have many organ systems, such as the circulatory system that transports blood throughout the body and to and from the lungs it includes organs such as the heart and blood vessels. Organisms are individual living entities. For example, each tree in a forest is an organism. Single-celled prokaryotes and single-celled eukaryotes are also considered organisms and are typically referred to as microorganisms.

Figure 2.6 From an atom to the entire Earth, biology examines all aspects of life. (credit “molecule”: modification of work by Jane Whitney credit “organelles”: modification of work by Louisa Howard credit “cells”: modification of work by Bruce Wetzel, Harry Schaefer, National Cancer Institute credit “tissue”: modification of work by “Kilbad”/Wikimedia Commons credit “organs”: modification of work by Mariana Ruiz Villareal, Joaquim Alves Gaspar credit “organisms”: modification of work by Peter Dutton credit “ecosystem”: modification of work by “gigi4791″/Flickr credit “biosphere”: modification of work by NASA)

All the individuals of a species living within a specific area are collectively called a population. For example, a forest may include many white pine trees. All of these pine trees represent the population of white pine trees in this forest. Different populations may live in the same specific area. For example, the forest with the pine trees includes populations of flowering plants and also insects and microbial populations. A community is the set of populations inhabiting a particular area. For instance, all of the trees, flowers, insects, and other populations in a forest form the forest’s community. The forest itself is an ecosystem. An ecosystem consists of all the living things in a particular area together with the abiotic, or non-living, parts of that environment such as nitrogen in the soil or rainwater. At the highest level of organization (Figure 2.6), the biosphere is the collection of all ecosystems, and it represents the zones of life on Earth. It includes land, water, and portions of the atmosphere.

It is important to note that the structural arrangement and functional properties of one level in the hierarchy of biological organization are important to the structure and function of the next level. New properties emerge (called emergent properties) at the next level as the individual parts interact that are not seen at the levels below. For example, cells such as neurons do not have the property of thinking. But if the neurons are arranged into nervous tissue and then into the organ, the brain, the emergent property of thinking becomes evident.


Nomenclature Plants: History, Common Names and Advantages | Botany

Let us learn about Nomenclature Plants. After reading this article you will learn about: 1. History of Nomenclature Plants 2. Common Names of the Nomenclature Plants 3. Botanical Names 4. International Rules 5. Main Points of the International Code 6. Advantages of Binomial System.

History of Nomenclature Plants:

The present day binomial system of nomenclature has a long evolutionary development. In near about 200 B.C. Cato in his monumental work ‘De Re Rustica’ used two names for plants, although he lacked the modern concept of genera and species. Later on the descriptive Greek nouns used for genera were translated into Latin, where it took the form of two words, i.e., binary generic names.

According to another tendency a descriptive phrase was given for the specific name. These methods resulted in the so called polynomials. In the middle of sixteenth century, Brunfels changed many binary generic names to single ones. A few years later Dodonaeus followed the binomial usage similar in principal to that of today’s binomial system of nomenclature.

Gaspard Bauhin wrote his monumental work ‘Pinax’ in 1623, in which he has given a list of about 6,000 plants. He used the binomial system extensively to give names to the plants.

None of these workers could make a permanent impression upon the botanical world of that time and works of the writers of those days continued to appear having mixed usage— monomial, binomial, trinomial and polynomial.

In those times the names of the plants were composed of several words in a series, constituting more or less a description of the plants. In 1753 Linnaeus published his great work ‘Species Plantaruni where he employed the binomial system to name the plants in true sense.

Augustin de Candolle’s Theorie elementaire de la botanique published in 1813 provided the first significant work since the publications of Linnaeus on nomenclature and morphology of the plants. In this work for the first time, a complete and detailed set of rules on plant nomenclature was given.

In 1821, Stendel’s Nomenclator botanicus was published, which comprised a list of the Latin names of all flowering plants known by then. The second edition of this work appeared in 1840. Nomenclature was used universally by the botanists, and formed the basis of the Index Kewensis.

Common Names of the Nomenclature Plants:

The plants have been provided with names by the different people of the different regions of the world in their own languages. These common or local names of the plants have their own weaknesses.

There are three main defects in common names:

(i) They may be quite indefinite, e.g., Pansy has been provided with fifty English names,

(ii) They are restricted to the people of one language or even one section of a country.

(iii) They are not regulated by any constituted authority. These common names give great trouble to a plant collector in a foreign country. There he feels the local names to be more difficult than the botanical names.

Botanical Names of the Nomenclature Plants:

At the present time each kind of plant is given a generic name followed by a specific name or epithet. The generic name is a noun, and the specific epithet is an adjective indicating which of the several members of the genus has been considered. The genus name is always capitalized.

The modern tendency is not to capitalize the specific name regardless of its derivation. Binomials are frequently descriptive of the plants and are usually derived from Greek or Latin, since these languages are internationally known by scholars. For example Coffea arabica Linn., stands for coffee Ficus elastica Roxb., for India rubber, Helianthus annuus Linn., for sunflower, etc.

Binomials when written should always be underlined and when printed they must be in italicized type. The name or the abbreviated name of the scientist who first described the species follows the binomial-such as Coffea arabica Linn. Mangifera Indica Linn. Rosa alba Linn. Santalum album Linn., etc. Linn., stands for the name of the great taxonomist Linnaeus Albizia procera Benth. Aloe barbadensis Mill. Kochia indica Wight Mussaenda glabrala Hutch. Solarium grandiflorum Ruiz and Pav., here each binomial is followed by the abbreviated name of the scientist who first described the species.

Some binomials are followed by two names, the first of which is within the brackets, thus Albizia lebbeck (Linn.) Benth. The name within brackets is that of the person who first described the species. The name which follows the parenthesis is that of the person who is responsible for the currently recognized binomial.

Accordingly, Linnaeus described the plant for the first time and Bentham corrected the name later on. The other such examples are – Albizia chinensis (Osbeck) Merr. Alocacia indica (Roxb.) Schott. Amorphophallus campanulatus (Roxb.) Blume ex Dene Brassica juncea (Linn.) Czern. and Cors. var. Cuneifolia Roxb. Butea monosperma (Lamk.) Taubert Feronia limonia (Linn.) Swingle, etc.

The reason for such author citations aids the taxonomist in finding the original and subsequent descriptions of a plant when necessary, and to avoid confusion when different workers use the same binomial accidentally to name different species. To aid the taxonomist further, the year in which the plant was described is sometimes written after the author’s name following the binomial.

International Rules of Botanical Nomenclature:

In 1950, the seventh international botanical congress was held at Stockholm and the rules of nomenclature were the subject of lengthy and considered discussions. Many minor changes and refinements were legislated.

Thereafter in 1956 the rules have been propounded by Lanjouw as the result of thorough study of many years.

1. Long generic names with difficult pronunciation must be avoided

2. A generic and a specific name is given to a perfectly named plant

3. The specific name must differentiate a plant from all allied species

4. The species is not distinguished by its size

5. The specific differences of a plant have no concern with the original place of the plant

6. colour should not be treated as a specific difference

7. Each plant species must possess a generic name

8. The generic name must be followed by a specific name

9. The shorter specific name is always well and good.

The above Linnean principles are quite simple, the role of codifying such rules has been taken up by various International Congresses, which have clarified some rules, modified others, and when necessary have established new ones. In all these changes the main aim has been to produce a uniform system.

The 1956 edition of the code gives detailed instructions on the steps to be taken when any change appears necessary. Such a change is first proposed to the various nomenclature committees elected by the International Botanical Congress and these committees make their recommendations on the subject in preliminary way.

The recommendations are then submitted to a vote by post from all the members of the International Association for Plant Taxonomy, from the authors themselves, and from the members of the committees.

During the International Botanical Congress all officially enrolled members of the Section cast their final vote. After the inception of the journal ‘Taxon’, every change that has been proposed is fully discussed in the journal before any decision is taken on the subject. Any proposal for a change receives full consideration before it is put up for confirmation or rejection during the session of the congress.

It is to be noted that during the last three or four International Botanical Congresses there have been but few changes, except perhaps in the rearrangement of the code and in some less important points of nomenclature.

Main Points of the International Code for Nomenclature Plants:

The code is divided into three parts:

In addition there are few interesting appendices. The principles are basic points on which the code is based. They do not give detailed rules about nomenclature, but show the main ideas that have guided the compilers of the Code, and should be kept in view by any botanist attempting to publish a new taxon.

According to this section of the code, every taxon or group of plants can bear only one correct name and vice versa a name could be applied to one group of plants. The rules give detailed prescriptions on all the points connected with the naming of plants. The recommendations are practical applications of the rules.

Some More Important Rules:

1. The rank of taxa:

In the 1956 edition of the code, the word ‘taxon’ has been introduced for the first time, to signify “taxonomic groups of any rank” (Article 1). The rank of species is basic one or more species make up a genus one or more genera make up a family, one or more families form an order, one or more orders make up a class, one or more classes make up a division-, several divisions make up the Vegetable Kingdom.

It is to be noted that the Code does not recognize “Natural Order”, a term often used in older books for the modem equivalent of “family” of the code.

The code has special provisions for the naming of the various taxa. The names of families must ordinarily end in – aceae, those of orders in – ales, and both should be treated as feminine plural nouns. Accordingly it is wrong to say, e.g., “The Amaranthaceae consists often genera.

” The correct way is to say, “The Amaranthaceae consist of ten genera” or the Papilionaceae are a family of the Leguminosae, which include two other families, Caesalpiniaceae and Mimosaceae.” Names of sub-families, e.g., Amaranthoideae of tribes, e.g., Amarantheae of sub-tribes, e.g., Amaranthinae, are all plural names and should be treated like the name of the family in this respect.

2. The type method:

This is a modification introduced in the code. According to Principle II, “The application of name of taxonomic groups is determined by means of nomenclatural types.” This means that when a species is described as new, the author must indicate which is the type of specimen on which the new species is based.

In the case of species, the type is an individual specimen, which is the type specimen on which the new species is based. In the small herbaceous plants all mounted on one herbarium sheet, the whole sheet may be marked as the type. When a specimen cannot be preserved, an illustration or figure or a description may be a type. The type of a genus is a species that of a family is a genus.

In the nomenclature of types, several terms are used which are as follows:

The type or holotype is the one element chosen by the author as the nomenclatural type. An isotype is a duplicate of the type or holotype, e.g., if several branches of a tree are collected at the same time, one specimen may be chosen as the type, the rest are isotypes.

Similarly, if a number of small herbaceous plants are collected at the same time, all belonging to the same new species, one may be selected as the holotype, the rest are isotypes. If they are mounted on the same herbarium sheet, they may be all part of the holotype (Article, 10).

A ‘paratype’ is a “specimen cited with the original description other than the holotype or isotype(s).” A paratype usually is a specimen from a collection other than the type on which the description of the new taxon has been based. Thus, there can be only one sheet of holotype, whereas a number of sheets of isotypes and paratypes.

When an author describes a new species and cites two or more specimens, they become the syntypes, if none of them individually has been designated the type or if more than one has been so designated.

“A lectotype is a specimen or other element selected from the original material to serve as nomenclatural type when the holotype was not designated at the time of publication or for so long as it is missing.” When two or more specimens have been designated as types by the author, they become syntypes, and one must be chosen as a lectotype.

However, when all the material, on which the description of a new species was based, is missing, then a neo-type must be selected, and the selection once made must be followed by subsequent taxonomists. This seems to be the case with many of the new taxa described by Roxburgh (1814), for which no actual specimen was either designated or preserved.

The fixing of the type specimen for a species or of the type in general for taxa below the rank of order is considered so important in the Code that Article 35 prescribes that “publication on or after January 1, 1958, of the name of a new taxon of recent plants of the rank of order or below is valid only when the nomenclatural type is indicated.” (Santapau, 1959)

With a few exceptions, where alternative names are permitted, each taxon of plants can bear only one correct name “the correct name is the earliest legitimate one validly published except in cases of limitation of priority by conservation.”

“The name of a species is a binary combination consisting of the name of the genus followed by a single specific epithet” (Article, 23). The Code gives to authors very great latitude in the selection of names, always provided that the specific name has not been used previously in the genus.

There is one case, however, which is specifically condemned as illegitimate and that is the use of tautonyms, i.e., when the specific name repeats unaltered the generic name, e.g., Malus malus Britt. This method is accepted in zoological nomenclature, where such names are coined, e.g., Turdus turdus or Corvus corvus, etc.

In botanical nomenclature, however, this is condemned. Art., 70(4). Thus, doubts have arisen about the validity of such names as Sesbania sesban or Samanea saman, etc.

Some authors have expressed strongly against such names, while on the other hand, Merrill (1912, 1916) accepts them as valid on the ground that a tautonym is only a name that repeats unaltered the generic name, and the names mentioned above do not repeat the generic name in full. Thus, such names can be taken as valid until a further, International Botanical Congress decides the matter.

5. Names of families:

The name of a family is a plural adjective and is formed by adding the suffix-aceae to the stem of a legitimate name of an included genus, e.g., Rosaceae from Rosa, Linaceae from Linum and Cucurbitaceae from Cucurbita.

The new names of the following eight families are:

6. Names of infra-specific taxa:

There is one case where repetition of the names is not only allowed, but ordered. Article 26 prescribes that the name of an infra-specific taxon (i.e., sub­species, variety or form) must be the same as that of the higher taxon, if the lower taxon includes the type of the higher one.

Thus, if a species is divided into varieties, the one that contains the type of the species must be called by the same name as the species and not var., genuina or var., typica (Art., 71), as often used to be called before.

For example, Carissa congesta Wt., of Khandala on the Western Ghats has two varieties:

(i) The typical plant, var., congesta (without name of author after the variety) and (ii) Var., albida Sant.

If the species has been divided into sub-species, varieties, forms, etc., then a plant is called Carissa congesta Wt., subsp., congesta, var., congesta, f., congesta, if the type of each higher rank is included in the lower division, the name Andropogon sorghum subsp., halepensis (L) Hackel var., halepensis is legitimate since the subspecies and the variety have the same type and the epithet must be repeated under (Art., 26 Art. 27, Santapau).

7. Effective and valid publication of new taxa:

Publication is effective when one can expect that the general botanical public may come to know of the publication (Santapau). According to Art., 29, publication is effective only when printed matter is distributed to the general public or atleast to botanical institutions with libraries accessible to botanists.

It is not effective by communication of a new names at a public meeting such as during the annual session of the Indian Science Congress, nor by placing of names in collections or gardens open to the public as for instance by labelling one’s specimens and placing them in public herbaria, where visitors may see the names. The date of the effective publication is the date on which the printed matter became available.

The following are the conditions attached to the publication of new taxa for validity.

1. Publication must be effective.

2. There must be a description of the new taxon, or a reference to a previously and effectively published description.

3. A combination is not validly published unless the author actually makes it (Art., 32).

4. Publication must be done in Latin (Art., 34) or with reference to a previously published Latin description.

5. When all the conditions for valid publication are not fulfilled at one and the same time, publication becomes valid when the last condition has been fulfilled. Thus, a publication is invalid if a botanist forgets to indicate the type of his new taxa, but it becomes valid when the type of the taxon has been indicated. The date of such publication will be when the type was indicated.

8. Changes in name when taxa are divided fused or altered:

When a genus is divided into two or more genera, or a species is split into two or more species, the original generic or specific name must be retained for the new taxon containing the type this applies also to infra-specific taxa.

When a section of a genus or species is transferred to another genus or species without alteration in rank, the original name must be retained whenever possible.

When the rank of a genus or infra-generic taxon is changed, the correct name or epithet is the earliest legitimate one available in the new rank.

When taxa of the same rank are united into one, the oldest legitimate name must be used for the new combined taxon, if the names are of the same date, the author who first unites them has the right to choose one of the names and his choice must be followed by subsequent botanists.

9. Form and spelling of names:

As per Code, authors have full liberty to coin their names. Authors are recommended not to make such names too long, nor too difficult to pronounce. In any case such names should be treated as Latin names.

When the name is actually taken from the Latin language, it retains the original gender and spelling. When the name is taken from the vernaculars, the author assigns a gender to it, and this must be followed by subsequent botanists. Names of genera and higher taxa are written with a capital initial letter. Specific names should be written with a small initial letter.

Advantages of Binomial System of Nomenclature Plants:

The binomials are more definite and precise than the common names. They are usually derived from Greek or Latin, since these languages are internationally known by scholars. They are frequently descriptive of the organism or plants. They and the taxonomists in finding the original and subsequent descriptions which indicate the systematic relationships.


Contents

In 1758, the Swedish botanist and zoologist Carl Linnaeus published in his Systema Naturae the two-word naming of species (binomial nomenclature). Canis is the Latin word meaning "dog," [13] and under this genus, he listed the domestic dog, the grey wolf, and the golden jackal. He classified the domestic dog as Canis familiaris and, on the next page, classified the grey wolf as Canis lupus. [2] Linnaeus considered the dog to be a separate species from the wolf because of its upturning tail (cauda recurvata), which is not found in any other canid. [14]

In 1999, a study of mitochondrial DNA (mtDNA) indicated that the domestic dog may have originated from the grey wolf, with the dingo and New Guinea singing dog breeds having developed at a time when human communities were more isolated from each other. [15] In the third edition of Mammal Species of the World published in 2005, the mammalogist W. Christopher Wozencraft listed under the wolf Canis lupus its wild subspecies and proposed two additional subspecies which formed the domestic dog clade: familiaris as named by Linneaus in 1758 and dingo named by Meyer in 1793. Wozencraft included hallstromi (the New Guinea singing dog) as another name (junior synonym) for the dingo. Wozencraft referred to the mtDNA study as one of the guides informing his decision. [3] Mammalogists have debated the inclusion of familiaris and dingo together under the "domestic dog" clade. [16] [17]

In 2019, a workshop hosted by the IUCN/Species Survival Commission's Canid Specialist Group considered the dingo and the New Guinea singing dog to be feral Canis familiaris and therefore did not assess them for the IUCN Red List. [18]

The Cretaceous–Paleogene extinction event occurred 65 million years ago and brought an end to the dinosaurs and the appearance of the first carnivorans. [19] The name carnivoran is given to a member of the order Carnivora. Carnivorans possess a common arrangement of teeth called carnassials, in which the first lower molar and the last upper premolar possess blade-like enamel crowns that act similar to a pair of shears for cutting meat. This dental arrangement has been modified by adaptation over the past 60 million years for diets composed of meat, for crushing vegetation, or for the loss of the carnassial function altogether as in seals, sea lions, and walruses. Today, not all carnivorans are carnivores, such as the insect-eating Aardwolf. [4]

The carnivoran ancestors of the dog-like caniforms and the cat-like feliforms began their separate evolutionary paths just after the end of the dinosaurs. The first members of the dog family Canidae appeared 40 million years ago, [20] of which only its subfamily the Caninae survives today in the form of the wolf-like and fox-like canines. Within the Caninae, the first members of genus Canis appeared six million years ago, [13] the ancestors of modern domestic dogs, wolves, coyotes, and golden jackals.

Domestication

The generally accepted earliest dog remains were discovered in Bonn-Oberkassel, Germany. Contextual, isotopic, genetic, and morphological evidence shows that this dog was not a local wolf. [21] The dog was dated to 14,223 years ago and was found buried along with a man and a woman, all three having been sprayed with red hematite powder and buried under large, thick basalt blocks. The dog had died of canine distemper. [22] Earlier remains dating back to 30,000 years ago have been described as Paleolithic dogs but their status as dogs or wolves remains debated [23] because considerable morphological diversity existed among wolves during the Late Pleistocene. [1]

This timing indicates that the dog was the first species to be domesticated [8] [7] in the time of hunter–gatherers, [6] which predates agriculture. [1] DNA sequences show that all ancient and modern dogs share a common ancestry and descended from an ancient, extinct wolf population which was distinct from the modern wolf lineage. [5] [6] Most dogs form a sister group to the remains of a Late Pleistocene wolf found in the Kessleroch cave near Thayngen in the canton of Schaffhausen, Switzerland, which dates to 14,500 years ago. The most recent common ancestor of both is estimated to be from 32,100 years ago. [24] This indicates that an extinct Late Pleistocene wolf may have been the ancestor of the dog, [7] [1] [25] with the modern wolf being the dog's nearest living relative. [7]

The dog is a classic example of a domestic animal that likely travelled a commensal pathway into domestication. [23] [26] The questions of when and where dogs were first domesticated have taxed geneticists and archaeologists for decades. [8] Genetic studies suggest a domestication process commencing over 25,000 years ago, in one or several wolf populations in either Europe, the high Arctic, or eastern Asia. [10] In 2021, a literature review of the current evidence infers that the dog was domesticated in Siberia 23,000 years ago by ancient North Siberians, then later dispersed eastward into the Americas and westward across Eurasia. [21]

Breeds

Dogs are the most variable mammal on earth with around 450 globally recognized dog breeds. [10] In the Victorian era, directed human selection developed the modern dog breeds, which resulted in a vast range of phenotypes. [7] Most breeds were derived from small numbers of founders within the last 200 years, [7] [10] and since then dogs have undergone rapid phenotypic change and were formed into today's modern breeds due to artificial selection imposed by humans. The skull, body, and limb proportions vary significantly between breeds, with dogs displaying more phenotypic diversity than can be found within the entire order of carnivores. These breeds possess distinct traits related to morphology, which include body size, skull shape, tail phenotype, fur type and colour. [7] Their behavioural traits include guarding, herding, and hunting, [7] retrieving, and scent detection. Their personality traits include hypersocial behavior, boldness, and aggression, [10] which demonstrates the functional and behavioral diversity of dogs. [7] As a result, today dogs are the most abundant carnivore species and are dispersed around the world. [10] The most striking example of this dispersal is that of the numerous modern breeds of European lineage during the Victorian era. [6]

Anatomy

Skeleton

All healthy dogs, regardless of their size and type, have an identical skeletal structure with the exception of the number of bones in the tail, although there is significant skeletal variation between dogs of different types. [27] [28] The dog’s skeleton is well adapted for running the vertebrae on the neck and back have extensions for powerful back muscles to connect to, the long ribs provide plenty of room for the heart and lungs, and the shoulders are unattached to the skeleton allowing great flexibility. [27] [28]

Compared to the dog's wolf like ancestors, selective breeding since domestication has seen the dog’s skeleton greatly enhanced in size for larger types as mastiffs and miniaturised for smaller types such as terriers dwarfism has been selectively utilised for some types where short legs are advantageous such as dachshunds and corgis. [28] Most dogs naturally have 26 vertebrae in their tails, but some with naturally short tails have as few as three. [27]

The dog's skull has identical components regardless of breed type, but there is significant divergence in terms of skull shape between types. [28] [29] The three basic skull shapes are the elongated dolichocephalic type as seen in sighthounds, the intermediate mesocephalic or mesaticephalic type, and the very short and broad brachycephalic type exemplified by mastiff type skulls. [28] [29]

Senses

A dog's senses include vision, hearing, smell, taste, touch, and sensitivity to Earth's magnetic field. Another study has suggested that dogs can see Earth's magnetic field. [30]

The coats of domestic dogs are of two varieties: "double" being familiar with dogs (as well as wolves) originating from colder climates, made up of a coarse guard hair and a soft down hair, or "single," with the topcoat only. Breeds may have an occasional "blaze," stripe, or "star" of white fur on their chest or underside. [31] Premature graying can occur in dogs from as early as one year of age this is associated with impulsive behaviors, anxiety behaviors, fear of noise, and fear of unfamiliar people or animals. [32]

There are many different shapes for dog tails: straight, straight up, sickle, curled, or corkscrew. As with many canids, one of the primary functions of a dog's tail is to communicate their emotional state, which can be crucial in getting along with others. In some hunting dogs the tail is traditionally docked to avoid injuries.

Health

Some breeds of dogs are prone to specific genetic ailments such as elbow and hip dysplasia, blindness, deafness, pulmonic stenosis, cleft palate, and trick knees. Two severe medical conditions significantly affecting dogs are pyometra, affecting unspayed females of all breeds and ages, and Gastric dilatation volvulus (bloat), which affects larger breeds or deep-chested dogs. Both of these are acute conditions and can kill rapidly. Dogs are also susceptible to parasites such as fleas, ticks, mites, hookworms, tapeworms, roundworms, and heartworms, which is a roundworm species that lives in the hearts of dogs.

Several human foods and household ingestibles are toxic to dogs, including chocolate solids, causing theobromine poisoning, onions and garlic, causing thiosulphate, sulfoxide or disulfide poisoning, grapes and raisins, macadamia nuts, and xylitol. [33] The nicotine in tobacco can also be dangerous to dogs. Signs of ingestion can include copious vomiting (e.g., from eating cigar butts) or diarrhea. Some other symptoms are abdominal pain, loss of coordination, collapse, or death. [34] [ page needed ]

Dogs are also vulnerable to some of the same health conditions as humans, including diabetes, dental and heart disease, epilepsy, cancer, hypothyroidism, and arthritis. [ citation needed ]

Lifespan

In 2013, a study found that mixed-breed dogs live on average 1.2 years longer than purebred dogs. Increasing body weight was negatively correlated with longevity (i.e., the heavier the dog, the shorter its lifespan). [35] The typical lifespan of dogs varies widely among breeds, but for most, the median longevity, the age at which half the dogs in a population have died and half are still alive, ranges from 10 to 13 years. [36] [37] The median longevity of mixed-breed dogs, taken as an average of all sizes, is one or more years longer than that of purebred dogs when all breeds are averaged. [36] [37] [38]

Reproduction

In domestic dogs, sexual maturity happens around six months to one year for both males and females, although this can be delayed until up to two years of age for some large breeds, and is the time at which female dogs will have their first estrous cycle. They will experience subsequent estrous cycles semiannually, during which the body prepares for pregnancy. At the peak of the cycle, females will become estrus, mentally and physically receptive to copulation. Because the ova survive and can be fertilized for a week after ovulation, more than one male can sire the same litter. [12]

Fertilization typically occurs two to five days after ovulation 14–16 days after ovulation, the embryo attaches to the uterus and after seven to eight more days, a heartbeat is detectable. [39] [40]

Dogs bear their litters roughly 58 to 68 days after fertilization, [12] [41] with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies. [42]

Neutering

Neutering refers to the sterilization of animals, usually by removing the male's testicles or the female's ovaries and uterus, to eliminate the ability to procreate and reduce sex drive. Because of dogs' overpopulation in some countries, many animal control agencies, such as the American Society for the Prevention of Cruelty to Animals (ASPCA), advise that dogs not intended for further breeding should be neutered, so that they do not have undesired puppies that may later be euthanized. [43]

According to the Humane Society of the United States, three to four million dogs and cats are euthanized each year. [44] Many more are confined to cages in shelters because there are many more animals than there are homes. Spaying or castrating dogs helps keep overpopulation down. [45]

Neutering reduces problems caused by hypersexuality, especially in male dogs. [46] Spayed female dogs are less likely to develop cancers affecting the mammary glands, ovaries, and other reproductive organs. [47] [ page needed ] However, neutering increases the risk of urinary incontinence in female dogs [48] and prostate cancer in males [49] and osteosarcoma, hemangiosarcoma, cruciate ligament rupture, obesity, and diabetes mellitus in either sex. [50]

Inbreeding depression

A common breeding practice for pet dogs is mating between close relatives (e.g., between half and full siblings). [51] Inbreeding depression is considered to be due mainly to the expression of homozygous deleterious recessive mutations. [52] Outcrossing between unrelated individuals, including dogs of different breeds, results in the beneficial masking of deleterious recessive mutations in progeny. [53]

In a study of seven dog breeds (the Bernese Mountain Dog, Basset Hound, Cairn Terrier, Brittany, German Shepherd Dog, Leonberger, and West Highland White Terrier), it was found that inbreeding decreases litter size and survival. [54] Another analysis of data on 42,855 Dachshund litters found that as the inbreeding coefficient increased, litter size decreased and the percentage of stillborn puppies increased, thus indicating inbreeding depression. [55] In a study of Boxer litters, 22% of puppies died before reaching 7 weeks of age. Stillbirth was the most frequent cause of death, followed by infection. Mortality due to infection increased significantly with increases in inbreeding. [56]

Intelligence

Dog intelligence is the dog's ability to perceive information and retain it as knowledge for applying to solve problems. Studies of two dogs suggest that dogs can learn by inference and have advanced memory skills. A study with Rico, a Border Collie, showed that he knew the labels of over 200 different items. He inferred the names of novel things by exclusion learning and correctly retrieved those new items immediately and four weeks after the initial exposure. A study of another Border Collie, "Chaser," documented his learning and memory capabilities. He had learned the names and could associate by verbal command over 1,000 words. [57] Dogs can read and react appropriately to human body language such as gesturing and pointing and human voice commands.

One study of canine cognitive abilities found that dogs' capabilities are no more exceptional than those of other animals, such as horses, chimpanzees, or cats. [58] One limited study of 18 household dogs found that they lacked spatial memory, and were more focussed on the "what" of a task rather than the "where". [59]

Dogs demonstrate a theory of mind by engaging in deception. [60] An experimental study showed compelling evidence that Australian dingos can outperform domestic dogs in non-social problem-solving, indicating that domestic dogs may have lost much of their original problem-solving abilities once they joined up with humans. [61] Another study revealed that after undergoing training to solve a simple manipulation task, dogs faced with an insoluble version of the same problem look at the human, while socialized wolves do not. [62]

Behavior

Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and external stimuli. [63] As the oldest domesticated species, dogs' minds inevitably have been shaped by millennia of contact with humans. As a result of this physical and social evolution, dogs have acquired the ability to understand and communicate with humans more than any other species and they are uniquely attuned to human behaviors. [9] Behavioral scientists have uncovered a surprising set of social-cognitive abilities in domestic dogs. These abilities are not possessed by the dog's closest canine relatives or other highly intelligent mammals, such as great apes, but rather parallel to children's social-cognitive skills. [64]

Unlike other domestic species selected for production-related traits, dogs were initially selected for their behaviors. [65] [66] In 2016, a study found that only 11 fixed genes showed variation between wolves and dogs. These gene variations were unlikely to have been the result of natural evolution and indicate selection on both morphology and behavior during dog domestication. These genes have been shown to affect the catecholamine synthesis pathway, with the majority of the genes affecting the fight-or-flight response [66] [67] (i.e., selection for tameness) and emotional processing. [66] Dogs generally show reduced fear and aggression compared with wolves. [66] [68] Some of these genes have been associated with aggression in some dog breeds, indicating their importance in both the initial domestication and later in breed formation. [66] Traits of high sociability and lack of fear in dogs may include genetic modifications related to Williams-Beuren syndrome in humans, which cause hypersociability at the expense of problem-solving ability. [69]

Communication

Dog communication is how dogs convey information to other dogs, understand messages from humans and translate the information that dogs are transmitting. [70] : xii Communication behaviors of dogs include eye gaze, facial expression, vocalization, body posture (including movements of bodies and limbs), and gustatory communication (scents, pheromones, and taste). Humans communicate to dogs by using vocalization, hand signals, and body posture.

Population

The dog is probably the most widely abundant large carnivoran living in the human environment. [71] [72] In 2013, an estimated global dog population was between 700 million [73] and 987 million. [74] Although it is said that the "dog is man's best friend," [75] this refers mainly to the

20% of dogs that live as pets in developed countries. [76] In the developing world, dogs are more commonly feral or communally owned, with pet dogs uncommon. Most of these dogs live their lives as scavengers and have never been owned by humans, with one study showing their most common response when approached by strangers is to run away (52%) or respond aggressively (11%). [77] Little is known about these dogs, or the dogs in developed countries that are feral, strays, or are in shelters because the great majority of modern research on dog cognition has focused on pet dogs living in human homes. [78]

Competitors and predators

Although dogs are the most abundant and widely distributed terrestrial carnivores, feral and free-ranging dogs' potential to compete with other large carnivores is limited by their strong association with humans. [71] For example, a review of the studies in dogs' competitive effects on sympatric carnivores did not mention any research on competition between dogs and wolves. [79] [80] Although wolves are known to kill dogs, they tend to live in pairs or in small packs in areas where they are highly persecuted, giving them a disadvantage facing large dog groups. [79] [81]

Wolves kill dogs wherever they are found together. [82] In some instances, wolves have displayed an uncharacteristic fearlessness of humans and buildings when attacking dogs to the extent that they have to be beaten off or killed. [83] Although the numbers of dogs killed each year are relatively low, it induces a fear of wolves entering villages and farmyards to take dogs and losses of dogs to wolves have led to demands for more liberal wolf hunting regulations. [79]

Coyotes and big cats have also been known to attack dogs. In particular, leopards are known to have a preference for dogs and have been recorded to kill and consume them, no matter what their size. [84] Siberian tigers in the Amur river region have killed dogs in the middle of villages. This indicates that the dogs were targeted. Amur tigers will not tolerate wolves as competitors within their territories, and the tigers could be considering dogs in the same way. [85] Striped hyenas are known to kill dogs in their range. [86]

Dogs have been described as omnivores. [12] [87] [88] Compared to wolves, dogs from agricultural societies have extra copies of amylase and other genes involved in starch digestion that contribute to an increased ability to thrive on a starch-rich diet. [11] Similar to humans, some dog breeds produce amylase in their saliva and are classified as having a high starch diet. [89] However, more like cats and less like other omnivores, dogs can only produce bile acid with taurine and they cannot produce vitamin D, which they obtain from animal flesh. Also, more like cats, dogs require arginine to maintain its nitrogen balance. These nutritional requirements place dogs halfway between carnivores and omnivores. [90]

Range

As a domesticated or semi-domesticated animal, the dog is nearly universal among human societies. Notable exceptions once included:

  • The Aboriginal Tasmanians, who were separated from Australia before the arrival of dingos on that continent
  • The Andamanese peoples, who were isolated when rising sea levels covered the land bridge to Myanmar
  • The Fuegians, who instead domesticated the Fuegian dog, a different canid species
  • Individual Pacific islands whose maritime settlers did not bring dogs, or where dogs died out after original settlement, notably the Mariana Islands, [91]Palau, [92] the Marshall Islands, [93] the Gilbert Islands, [93]New Caledonia, [94]Vanuatu, [94][95]Tonga, [95]Marquesas, [95]Mangaia in the Cook Islands, Rapa Iti in French Polynesia, Easter Island, [95] the Chatham Islands[96] and Pitcairn Island (settled by the Bounty mutineers, who killed off their dogs to escape discovery by passing ships). [97]

Dogs were introduced to Antarctica as sled dogs, but were later outlawed by international agreement due to the possible risk of spreading infections. [98]

Domestic dogs inherited complex behaviors, such as bite inhibition, from their wolf ancestors, which would have been pack hunters with a complex body language. These sophisticated forms of social cognition and communication may account for their trainability, playfulness and ability to fit into human households and social situations. These attributes have given dogs a relationship with humans that has enabled them to become one of the most successful animals today. [99]

The dogs' value to early human hunter-gatherers led to them quickly becoming ubiquitous across world cultures. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and the military, companionship and aiding disabled individuals. This influence on human society has given them the nickname "man's best friend" in the Western world. In some cultures, however, dogs are also a source of meat. [100] [101]

As pets

It is estimated that three-quarters of the world's dog population lives in the developing world as feral, village, or community dogs, with pet dogs uncommon. [102] [ page needed ]

"The most widespread form of interspecies bonding occurs between humans and dogs" [103] and the keeping of dogs as companions, particularly by elites, has a long history. [104] Pet dog populations grew significantly after World War II as suburbanization increased. [104] In the 1950s and 1960s, dogs were kept outside more often than they tend to be today [105] (the expression "in the doghouse" - recorded since 1932 [106] - to describe exclusion from the group implies a distance between the doghouse and the home) and were still primarily functional, acting as a guard, children's playmate, or walking companion. From the 1980s, there have been changes in the pet dog's role, such as the increased role of dogs in the emotional support of their human guardians. [107] [ page needed ] People and their dogs have become increasingly integrated and implicated in each other's lives [108] [ page needed ] to the point where pet dogs actively shape how a family and home are experienced. [109]

There have been two significant trends occurring within the second half of the 20th century in pet dogs' changing status. The first has been "commodification," shaping it to conform to social expectations of personality and behavior. [109] The second has been the broadening of the family's concept and the home to include dogs-as-dogs within everyday routines and practices. [109]

A vast range of commodity forms aims to transform a pet dog into an ideal companion. [110] The list of goods, services, and places available is enormous: from dog perfumes, couture, furniture and housing to dog groomers, therapists, trainers and caretakers, dog cafes, spas, parks and beaches and dog hotels, airlines and cemeteries. [110] Dog training books, classes, and television programs proliferated as the process of commodifying the pet dog continued. [111]

The majority of contemporary dog owners describe their pet as part of the family, although some ambivalence about the relationship is evident in the popular reconceptualization of the dog-human family as a pack. [109] Some dog trainers, such as on the television program Dog Whisperer, have promoted a dominance model of dog-human relationships. However, it has been disputed that "trying to achieve status" is characteristic of dog-human interactions. [112] Pet dogs play an active role in family life for example, a study of conversations in dog-human families showed how family members use the dog as a resource, talking to the dog, or talking through the dog to mediate their interactions with each other. [113]

Increasingly, human family-members engage in activities centered on the dog's perceived needs and interests, or in which the dog is an integral partner, such as dog dancing and dog yoga. [110]

According to statistics published by the American Pet Products Manufacturers Association in the National Pet Owner Survey in 2009–2010, an estimated 77.5 million people in the United States have pet dogs. [114] The same source shows that nearly 40% of American households own at least one dog, of which 67% own just one dog, 25% two dogs and nearly 9% more than two dogs. There does not seem to be any gender preference among dogs as pets, as the statistical data reveal an equal number of male and female pet dogs. Although several programs promote pet adoption, less than one-fifth of the owned dogs come from shelters. [114]

A study using magnetic resonance imaging (MRI) to compare humans and dogs showed that dogs have the same response to voices and use the same parts of the brain as humans do. This gives dogs the ability to recognize human emotional sounds, making them friendly social pets to humans. [115]

Dogs have lived and worked with humans in many roles. In addition to dogs' role as companion animals, dogs have been bred for herding livestock (collies, sheepdogs), [116] [ page needed ] [12] hunting (hounds, pointers) [117] [ page needed ] and rodent control (terriers). [12] Other types of working dogs include search and rescue dogs, [118] detection dogs trained to detect illicit drugs [119] or chemical weapons [120] guard dogs dogs who assist fishermen with the use of nets and dogs that pull loads. [12] In 1957, the dog Laika became the first animal to be launched into Earth orbit, aboard the Soviets' Sputnik 2 she died during the flight. [121] [122]

Various kinds of service dogs and assistance dogs, including guide dogs, hearing dogs, mobility assistance dogs and psychiatric service dogs, assist individuals with disabilities. [123] [124] Some dogs owned by people with epilepsy have been shown to alert their handler when the handler shows signs of an impending seizure, sometimes well in advance of onset, allowing the guardian to seek safety, medication, or medical care. [125]

Sports and shows

People often enter their dogs in competitions, such as breed-conformation shows or sports, including racing, sledding and agility competitions. In conformation shows, also referred to as breed shows, a judge familiar with the specific dog breed evaluates individual purebred dogs for conformity with their established breed type as described in the breed standard. As the breed standard only deals with the dog's externally observable qualities (such as appearance, movement and temperament), separately tested qualities (such as ability or health) are not part of the judging in conformation shows.

As food

Dog meat is consumed in some East Asian countries, including Korea, [126] [ page needed ] China [100] Vietnam [101] and the Philippines, [127] which dates back to antiquity. [128] Based on limited data, it is estimated that 13–16 million dogs are killed and consumed in Asia every year. [129] In China, debates have ensued over banning the consumption of dog meat. [130] Following the Sui and Tang dynasties of the first millennium, however, people living on northern China's plains began to eschew eating dogs, which is likely due to Buddhism and Islam's spread, two religions that forbade the consumption of certain animals, including the dog. As members of the upper classes shunned dog meat, it gradually became a social taboo to eat it, even though the general population continued to consume it for centuries afterward. [131] Dog meat is also consumed in some parts of Switzerland. [132] Other cultures, such as Polynesia and pre-Columbian Mexico, also consumed dog meat in their history. Dog fat is also reportedly believed to be beneficial for the lungs in some parts of Poland [133] [134] and Central Asia. [135] [136] Proponents of eating dog meat have argued that placing a distinction between livestock and dogs is Western hypocrisy and that there is no difference in eating different animals' meat. [137] [138] [139] [140]

In Korea, the primary dog breed raised for meat, the Nureongi, differs from those breeds raised for pets that Koreans may keep in their homes. [141]

The most popular Korean dog dish is called bosintang, a spicy stew meant to balance the body's heat during the summer months. Followers of the custom claim this is done to ensure good health by balancing one's gi, or the body's vital energy. A 19th-century version of bosintang explains that the dish is prepared by boiling dog meat with scallions and chili powder. Variations of the dish contain chicken and bamboo shoots. While the dishes are still prevalent in Korea with a segment of the population, dog is not as widely consumed as beef, pork and chicken. [141]

Health risks to humans

In 2018, the WHO reported that 59,000 people died globally from rabies, with 59.6% in Asia and 36.4% in Africa. Rabies is a disease for which dogs are the most important vector. [142] Significant dog bites affect tens of millions of people globally each year. Children in mid-to-late childhood are the largest percentage bitten by dogs, with a greater risk of injury to the head and neck. They are more likely to need medical treatment and have the highest death rate. [143] Sharp claws with powerful muscles behind them can lacerate flesh in a scratch that can lead to serious infections. [144]

In the U.S., cats and dogs are a factor in more than 86,000 falls each year. [145] It has been estimated that around 2% of dog-related injuries treated in U.K. hospitals are domestic accidents. The same study found that while dog involvement in road traffic accidents was difficult to quantify, dog-associated road accidents involving injury more commonly involved two-wheeled vehicles. [146]

Toxocara canis (dog roundworm) eggs in dog feces can cause toxocariasis. In the United States, about 10,000 cases of Toxocara infection are reported in humans each year, and almost 14% of the U.S. population is infected. [147] Untreated toxocariasis can cause retinal damage and decreased vision. [148] Dog feces can also contain hookworms that cause cutaneous larva migrans in humans. [149] [150]

Health benefits for humans

Dogs suffer from the same common disorders as humans these include cancer, diabetes, heart disease and neurologic disorders. Their pathology is similar to humans, as is their response to treatment and their outcomes. Researchers are identifying the genes associated with dog diseases similar to human disorders, but lack mouse models to find cures for both dogs and humans. The genes involved in canine obsessive-compulsive disorders led to the detection of four genes in humans' related pathways. [10]

The scientific evidence is mixed as to whether a dog's companionship can enhance human physical health and psychological well-being. [151] Studies suggesting that there are benefits to physical health and psychological well-being [152] have been criticized for being poorly controlled. [153] It found that "the health of elderly people is related to their health habits and social supports but not to their ownership of, or attachment to, a companion animal." Earlier studies have shown that people who keep pet dogs or cats exhibit better mental and physical health than those who do not, making fewer visits to the doctor and being less likely to be on medication than non-guardians. [154]

A 2005 paper states "recent research has failed to support earlier findings that pet ownership is associated with a reduced risk of cardiovascular disease, a reduced use of general practitioner services, or any psychological or physical benefits on health for community dwelling older people. Research has, however, pointed to significantly less absenteeism from school through sickness among children who live with pets." [151] In one study, new guardians reported a highly significant reduction in minor health problems during the first month following pet acquisition. This effect was sustained in those with dogs through to the end of the study. [155]

People with pet dogs took considerably more physical exercise than those with cats and those without pets. The results provide evidence that keeping pets may have positive effects on human health and behavior and that for guardians of dogs, these effects are relatively long-term. [155] Pet guardianship has also been associated with increased coronary artery disease survival. Human guardians are significantly less likely to die within one year of an acute myocardial infarction than those who did not own dogs. [156]

The health benefits of dogs can result from contact with dogs in general, not solely from having dogs as pets. For example, when in a pet dog's presence, people show reductions in cardiovascular, behavioral and psychological indicators of anxiety. [157] Other health benefits are gained from exposure to immune-stimulating microorganisms, which can protect against allergies and autoimmune diseases according to the hygiene hypothesis. The benefits of contact with a dog also include social support, as dogs cannot only provide companionship and social support themselves but also act as facilitators of social interactions between humans. [158] One study indicated that wheelchair users experience more positive social interactions with strangers when accompanied by a dog than when they are not. [159] In 2015, a study found that pet owners were significantly more likely to get to know people in their neighborhood than non-pet owners. [160]

Using dogs and other animals as a part of therapy dates back to the late 18th century, when animals were introduced into mental institutions to help socialize patients with mental disorders. [161] Animal-assisted intervention research has shown that animal-assisted therapy with a dog can increase social behaviors, such as smiling and laughing, among people with Alzheimer's disease. [162] One study demonstrated that children with ADHD and conduct disorders who participated in an education program with dogs and other animals showed increased attendance, increased knowledge and skill objectives and decreased antisocial and violent behavior compared with those not in an animal-assisted program. [163]


Chapter 2 Summary

In this chapter, you learned about the basic principles of biology and how humans are situated among other living organisms. Specifically, you learned:

  • To be classified as a living thing, most scientists agree that an object must exhibit seven characteristics, including:
    • Maintaining a more-or-less constant internal environment, which is called homeostasis.
    • Having multiple levels of organization and consisting of one or more cells.
    • Using energy and being capable of metabolism.
    • Being able to grow and develop.
    • Being capable of evolving adaptations to the environment.
    • Being able to detect and respond to environmental stimuli.
    • Being capable of reproducing, which is the process by which living things give rise to offspring.
    • According to cell theory, all living things are made of cells and come from other living cells.
    • Gene theory states that the characteristics of living things are controlled by genes that pass from parents to offspring.
    • All living things — and even the entire biosphere — strive to maintain homeostasis.
    • The characteristics of living things change over time as they evolve, and some acquire adaptations or traits that better suit them to a given environment.

    Now you understand the basic principles of biology and some of the characteristics of living organisms. In the next chapter, you will learn about the molecules that make up living organisms, as well as the chemistry that allows organisms to exist and function.


    Examples of Binomial Nomenclature

    Felis concolor

    The scientific name Homo sapiens is used to describe the human species. It combines parts of the Latin words hom, meaning human, and sapien, meaning wise. This descriptor of humans tells us many things about the species. First and foremost it defines humans as part of the genus Homo, which includes several extinct species of early humans and modern humans. While we are the only living species in the genus Homo, the specific epithet describes our supposed separation from other species in the genus. Homo neaderthalensis for example, is hypothesized to have gone extinct because of competition from Homo sapiens, or modern humans. Many theorize that it was advanced tool use and language in Homo sapiens that gave them an edge. Modern DNA analysis has shown that Neanderthal genes still exist within the human population, suggesting the two may have interbred at certain points. The binomial nomenclature used here serves to clarify between different forms of organisms through evolutionary time, as well as clarify that all humans are being discussed.


    Binomial Classification

    The binomial classification system proposed by Linnaeus allowed him and others to group organisms together based on common structures, functions, and resulting behaviors, which led to the science of taxonomy, or classification.

    Often biologists use a taxonomic key, also known as a dichotomous key, to identify unknown organisms by their physical characteristics. Taxonomic keys work on a base-two premise: The organism either has the characteristic or does not. The resulting answer then directs the biologist to the next set of questions until all the characteristics have been accounted for and the organism is identified. The following Binomial classification illustration is a fictitious key that demonstrates the process.

    Try using the following taxonomic key to identify which organism is a ?dumlop.?

    CharacteristicOrganism
    1a.It has two legs.Zembo
    1b.It has more than two legs.Go to 2
    2a.It is shaded.Go to 3
    2b.It is not shaded.Go to 4
    3a.It has a round head.Dumlop
    3b.It does not have a round head.Gorgot

    Backtracking from the dichotomous key, a dumlop is an organism that has more than two legs, is shaded, with a round head. Most dichotomous keys are quite lengthy, to account for all the features that a set of organisms may possess. The broadest keys begin at the kingdom level and proceed to the more specific genus and species levels.


    Contents

    Coyote males average 8 to 20 kg (18 to 44 lb) in weight, while females average 7 to 18 kg (15 to 40 lb), though size varies geographically. Northern subspecies, which average 18 kg (40 lb), tend to grow larger than the southern subspecies of Mexico, which average 11.5 kg (25 lb). Body length ranges on average from 1.0 to 1.35 m (3 ft 3 in to 4 ft 5 in), and tail length 40 cm (16 in), with females being shorter in both body length and height. [5] The largest coyote on record was a male killed near Afton, Wyoming, on November 19, 1937, which measured 1.5 m (4 ft 11 in) from nose to tail, and weighed 34 kg (75 lb). [6] Scent glands are located at the upper side of the base of the tail and are a bluish-black color. [7]

    The color and texture of the coyote's fur vary somewhat geographically. [5] The hair's predominant color is light gray and red or fulvous, interspersed around the body with black and white. Coyotes living at high elevations tend to have more black and gray shades than their desert-dwelling counterparts, which are more fulvous or whitish-gray. [8] The coyote's fur consists of short, soft underfur and long, coarse guard hairs. The fur of northern subspecies is longer and denser than in southern forms, with the fur of some Mexican and Central American forms being almost hispid (bristly). [9] Generally, adult coyotes (including coywolf hybrids) have a sable coat color, dark neonatal coat color, bushy tail with an active supracaudal gland, and a white facial mask. [10] Albinism is extremely rare in coyotes out of a total of 750,000 coyotes killed by federal and cooperative hunters between March 22, 1938, and June 30, 1945, only two were albinos. [8]

    The coyote is typically smaller than the gray wolf, but has longer ears and a relatively larger braincase, [5] as well as a thinner frame, face, and muzzle. The scent glands are smaller than the gray wolf's, but are the same color. [7] Its fur color variation is much less varied than that of a wolf. [11] The coyote also carries its tail downwards when running or walking, rather than horizontally as the wolf does. [12]

    Coyote tracks can be distinguished from those of dogs by their more elongated, less rounded shape. [13] [14] Unlike dogs, the upper canines of coyotes extend past the mental foramina. [5]

    History Edit

    At the time of the European colonization of the Americas, coyotes were largely confined to open plains and arid regions of the western half of the continent. [15] In early post-Columbian historical records, determining whether the writer is describing coyotes or wolves is often difficult. One record from 1750 in Kaskaskia, Illinois, written by a local priest, noted that the "wolves" encountered there were smaller and less daring than European wolves. Another account from the early 1800s in Edwards County mentioned wolves howling at night, though these were likely coyotes. [16] This species was encountered several times during the Lewis and Clark Expedition (1804–1806), though it was already well known to European traders on the upper Missouri. Meriwether Lewis, writing on 5 May 1805, in northeastern Montana, described the coyote in these terms:

    The small wolf or burrowing dog of the prairies are the inhabitants almost invariably of the open plains they usually associate in bands of ten or twelve sometimes more and burrow near some pass or place much frequented by game not being able alone to take deer or goat they are rarely ever found alone but hunt in bands they frequently watch and seize their prey near their burrows in these burrows, they raise their young and to them they also resort when pursued when a person approaches them they frequently bark, their note being precisely that of the small dog. They are of an intermediate size between that of the fox and dog, very active fleet and delicately formed the ears large erect and pointed the head long and pointed more like that of the fox tale long . the hair and fur also resembles the fox, tho' is much coarser and inferior. They are of a pale reddish-brown colour. The eye of a deep sea green colour small and piercing. Their [claws] are rather longer than those of the ordinary wolf or that common to the Atlantic states, none of which are to be found in this quarter, nor I believe above the river Plat. [17]

    The coyote was first scientifically described by naturalist Thomas Say in September 1819, on the site of Lewis and Clark's Council Bluffs, 24 km (15 mi) up the Missouri River from the mouth of the Platte during a government-sponsored expedition with Major Stephen Long. He had the first edition of the Lewis and Clark journals in hand, which contained Biddle's edited version of Lewis's observations dated 5 May 1805. His account was published in 1823. Say was the first person to document the difference between a "prairie wolf" (coyote) and on the next page of his journal a wolf which he named Canis nubilus (Great Plains wolf). [3] [18] Say described the coyote as:

    Canis latrans. Cinereous or gray, varied with black above, and dull fulvous, or cinnamon hair at base dusky plumbeous, in the middle of its length dull cinnamon, and at tip gray or black, longer on the vertebral line ears erect, rounded at tip, cinnamon behind, the hair dark plumbeous at base, inside lined with gray hair eyelids edged with black, superior eyelashes black beneath, and at tip above supplemental lid margined with black-brown before, and edged with black brown behind iris yellow pupil black-blue spot upon the lachrymal sac black-brown rostrum cinnamon, tinctured with grayish on the nose lips white, edged with black, three series of black seta head between the ears intermixed with gray, and dull cinnamon, hairs dusky plumbeous at base sides paler than the back, obsoletely fasciate with black above the legs legs cinnamon on the outer side, more distinct on the posterior hair: a dilated black abbreviated line on the anterior ones near the wrist tail bushy, fusiform, straight, varied with gray and cinnamon, a spot near the base above, and tip black the tip of the trunk of the tail, attains the tip of the os calcis, when the leg is extended beneath white, immaculate, tail cinnamon towards the tip, tip black posterior feet four toed, anterior five toed. [3]

    Naming and etymology Edit

    The earliest written reference to the species comes from the naturalist Francisco Hernández's Plantas y Animales de la Nueva España (1651), where it is described as a "Spanish fox" or "jackal". The first published usage of the word "coyote" (which is a Spanish borrowing of its Nahuatl name coyōtl pronunciation ( help · info ) ) comes from the historian Francisco Javier Clavijero's Historia de México in 1780. [19] The first time it was used in English occurred in William Bullock's Six months' residence and travels in Mexico (1824), where it is variously transcribed as cayjotte and cocyotie. The word's spelling was standardized as "coyote" by the 1880s. [17] [20] Alternative English names for the coyote include "prairie wolf", "brush wolf", "cased wolf", [21] [a] "little wolf" [22] and "American jackal". [23] Its binomial name Canis latrans translates to "barking dog", a reference to the many vocalizations they produce. [24]

    Evolution Edit

    Fossil record Edit

    Xiaoming Wang and Richard H. Tedford, one of the foremost authorities on carnivore evolution, [40] proposed that the genus Canis was the descendant of the coyote-like Eucyon davisi and its remains first appeared in the Miocene 6 million years ago (Mya) in the southwestern US and Mexico. By the Pliocene (5 Mya), the larger Canis lepophagus [41] appeared in the same region and by the early Pleistocene (1 Mya) C. latrans (the coyote) was in existence. They proposed that the progression from Eucyon davisi to C. lepophagus to the coyote was linear evolution. [42] Additionally, C. latrans and C. aureus are closely related to C. edwardii, a species that appeared earliest spanning the mid-Blancan (late Pliocene) to the close of the Irvingtonian (late Pleistocene), and coyote remains indistinguishable from C. latrans were contemporaneous with C. edwardii in North America. [43] Johnston describes C. lepophagus as having a more slender skull and skeleton than the modern coyote. [44] Ronald Nowak found that the early populations had small, delicate, narrowly proportioned skulls that resemble small coyotes and appear to be ancestral to C. latrans. [45]

    C. lepophagus was similar in weight to modern coyotes, but had shorter limb bones that indicate a less cursorial lifestyle. The coyote represents a more primitive form of Canis than the gray wolf, as shown by its relatively small size and its comparatively narrow skull and jaws, which lack the grasping power necessary to hold the large prey in which wolves specialize. This is further corroborated by the coyote's sagittal crest, which is low or totally flattened, thus indicating a weaker bite than the wolves. The coyote is not a specialized carnivore as the wolf is, as shown by the larger chewing surfaces on the molars, reflecting the species' relative dependence on vegetable matter. In these respects, the coyote resembles the fox-like progenitors of the genus more so than the wolf. [46]

    The oldest fossils that fall within the range of the modern coyote date to 0.74–0.85 Ma (million years) in Hamilton Cave, West Virginia 0.73 Ma in Irvington, California 0.35–0.48 Ma in Porcupine Cave, Colorado, and in Cumberland Cave, Pennsylvania. [47] Modern coyotes arose 1,000 years after the Quaternary extinction event. [48] Compared to their modern Holocene counterparts, Pleistocene coyotes (C. l. orcutti) were larger and more robust, likely in response to larger competitors and prey. [48] Pleistocene coyotes were likely more specialized carnivores than their descendants, as their teeth were more adapted to shearing meat, showing fewer grinding surfaces suited for processing vegetation. [49] Their reduction in size occurred within 1,000 years of the Quaternary extinction event, when their large prey died out. [48] Furthermore, Pleistocene coyotes were unable to exploit the big-game hunting niche left vacant after the extinction of the dire wolf (C. dirus), as it was rapidly filled by gray wolves, which likely actively killed off the large coyotes, with natural selection favoring the modern gracile morph. [49]

    DNA evidence Edit

    In 1993, a study proposed that the wolves of North America display skull traits more similar to the coyote than wolves from Eurasia. [50] In 2010, a study found that the coyote was a basal member of the clade that included the Tibetan wolf, the domestic dog, the Mongolian wolf and the Eurasian wolf, with the Tibetan wolf diverging early from wolves and domestic dogs. [51] In 2016, a whole-genome DNA study proposed, based on the assumptions made, that all of the North American wolves and coyotes diverged from a common ancestor less than 6,000–117,000 years ago. The study also indicated that all North American wolves have a significant amount of coyote ancestry and all coyotes some degree of wolf ancestry and that the red wolf and eastern wolf are highly admixed with different proportions of gray wolf and coyote ancestry. [52] [53] The proposed timing of the wolf/coyote divergence conflicts with the finding of a coyote-like specimen in strata dated to 1 Mya. [54]

    Genetic studies relating to wolves or dogs have inferred phylogenetic relationships based on the only reference genome available, that of the Boxer dog. In 2017, the first reference genome of the wolf Canis lupus lupus was mapped to aid future research. [55] In 2018, a study looked at the genomic structure and admixture of North American wolves, wolf-like canids, and coyotes using specimens from across their entire range that mapped the largest dataset of nuclear genome sequences against the wolf reference genome. The study supports the findings of previous studies that North American gray wolves and wolf-like canids were the result of complex gray wolf and coyote mixing. A polar wolf from Greenland and a coyote from Mexico represented the purest specimens. The coyotes from Alaska, California, Alabama, and Quebec show almost no wolf ancestry. Coyotes from Missouri, Illinois, and Florida exhibit 5–10% wolf ancestry. There was 40%:60% wolf to coyote ancestry in red wolves, 60%:40% in Eastern timber wolves, and 75%:25% in the Great Lakes wolves. There was 10% coyote ancestry in Mexican wolves and the Atlantic Coast wolves, 5% in Pacific Coast and Yellowstone wolves, and less than 3% in Canadian archipelago wolves. If a third canid had been involved in the admixture of the North American wolf-like canids then its genetic signature would have been found in coyotes and wolves, which it has not. [56]

    In 2018, whole genome sequencing was used to compare members of the genus Canis. The study indicates that the common ancestor of the coyote and gray wolf has genetically admixed with a ghost population of an extinct unidentified canid. The canid was genetically close to the dhole and had evolved after the divergence of the African wild dog from the other canid species. The basal position of the coyote compared to the wolf is proposed to be due to the coyote retaining more of the mitochondrial genome of this unknown canid. [57]

    Subspecies Edit

    As of 2005 [update] , 19 subspecies are recognized. [23] [58] Geographic variation in coyotes is not great, though taken as a whole, the eastern subspecies (C. l. thamnos and C. l. frustor) are large, dark-colored animals, with a gradual paling in color and reduction in size westward and northward (C. l. texensis, C. l. latrans, C. l. lestes, and C. l. incolatus), a brightening of ochraceous tones – deep orange or brown – towards the Pacific coast (C. l. ochropus, C. l. umpquensis), a reduction in size in Aridoamerica (C. l. microdon, C. l. mearnsi) and a general trend towards dark reddish colors and short muzzles in Mexican and Central American populations. [59]

    Hybridization Edit

    Coyotes have occasionally mated with domestic dogs, sometimes producing crosses colloquially known as "coydogs". [72] Such matings are rare in the wild, as the mating cycles of dogs and coyotes do not coincide, and coyotes are usually antagonistic towards dogs. Hybridization usually only occurs when coyotes are expanding into areas where conspecifics are few, and dogs are the only alternatives. Even then, pup survival rates are lower than normal, as dogs do not form pair bonds with coyotes, thus making the rearing of pups more difficult. [73] In captivity, F1 hybrids (first generation) tend to be more mischievous and less manageable as pups than dogs, and are less trustworthy on maturity than wolf-dog hybrids. [72] Hybrids vary in appearance, but generally retain the coyote's usual characteristics. F1 hybrids tend to be intermediate in form between dogs and coyotes, while F2 hybrids (second generation) are more varied. Both F1 and F2 hybrids resemble their coyote parents in terms of shyness and intrasexual aggression. [10] [74] Hybrids are fertile and can be successfully bred through four generations. [72] Melanistic coyotes owe their black pelts to a mutation that first arose in domestic dogs. [71] A population of nonalbino white coyotes in Newfoundland owe their coloration to a melanocortin 1 receptor mutation inherited from Golden Retrievers. [75]

    Coyotes have hybridized with wolves to varying degrees, particularly in eastern North America. The so-called "eastern coyote" of northeastern North America probably originated in the aftermath of the extermination of gray and eastern wolves in the northeast, thus allowing coyotes to colonize former wolf ranges and mix with the remnant wolf populations. This hybrid is smaller than either the gray or eastern wolf, and holds smaller territories, but is in turn larger and holds more extensive home ranges than the typical western coyote. As of 2010 [update] , the eastern coyote's genetic makeup is fairly uniform, with minimal influence from eastern wolves or western coyotes. [76] Adult eastern coyotes are larger than western coyotes, with female eastern coyotes weighing 21% more than male western coyotes. [76] [77] Physical differences become more apparent by the age of 35 days, with eastern coyote pups having longer legs than their western counterparts. Differences in dental development also occurs, with tooth eruption being later, and in a different order in the eastern coyote. [78] Aside from its size, the eastern coyote is physically similar to the western coyote. The four color phases range from dark brown to blond or reddish blond, though the most common phase is gray-brown, with reddish legs, ears, and flanks. [79] No significant differences exist between eastern and western coyotes in aggression and fighting, though eastern coyotes tend to fight less, and are more playful. Unlike western coyote pups, in which fighting precedes play behavior, fighting among eastern coyote pups occurs after the onset of play. [78] Eastern coyotes tend to reach sexual maturity at two years of age, much later than in western coyotes. [76]

    Eastern and red wolves are also products of varying degrees of wolf-coyote hybridization. The eastern wolf probably was a result of a wolf-coyote admixture, combined with extensive backcrossing with parent gray wolf populations. The red wolf may have originated during a time of declining wolf populations in the Southeastern Woodlands, forcing a wolf-coyote hybridization, as well as backcrossing with local parent coyote populations to the extent that about 75–80% of the modern red wolf's genome is of coyote derivation. [52] [80]

    Social and reproductive behaviors Edit

    Like the Eurasian golden jackal, the coyote is gregarious, but not as dependent on conspecifics as more social canid species like wolves are. This is likely because the coyote is not a specialized hunter of large prey as the latter species is. [81] The basic social unit of a coyote pack is a family containing a reproductive female. However, unrelated coyotes may join forces for companionship, or to bring down prey too large to attack singly. Such "nonfamily" packs are only temporary, and may consist of bachelor males, nonreproductive females and subadult young. Families are formed in midwinter, when females enter estrus. [22] Pair bonding can occur 2–3 months before actual copulation takes place. [82] The copulatory tie can last 5–45 minutes. [83] A female entering estrus attracts males by scent marking [84] and howling with increasing frequency. [23] A single female in heat can attract up to seven reproductive males, which can follow her for as long as a month. Although some squabbling may occur among the males, once the female has selected a mate and copulates, the rejected males do not intervene, and move on once they detect other estrous females. [22] Unlike the wolf, which has been known to practice both monogamous and bigamous matings, [85] the coyote is strictly monogamous, even in areas with high coyote densities and abundant food. [86] Females that fail to mate sometimes assist their sisters or mothers in raising their pups, or join their siblings until the next time they can mate. The newly mated pair then establishes a territory and either constructs their own den or cleans out abandoned badger, marmot, or skunk earths. During the pregnancy, the male frequently hunts alone and brings back food for the female. The female may line the den with dried grass or with fur pulled from her belly. [22] The gestation period is 63 days, with an average litter size of six, though the number fluctuates depending on coyote population density and the abundance of food. [23]

    Coyote pups are born in dens, hollow trees, or under ledges, and weigh 200 to 500 g (0.44 to 1.10 lb) at birth. They are altricial, and are completely dependent on milk for their first 10 days. The incisors erupt at about 12 days, the canines at 16, and the second premolars at 21. Their eyes open after 10 days, by which point the pups become increasingly more mobile, walking by 20 days, and running at the age of six weeks. The parents begin supplementing the pup's diet with regurgitated solid food after 12–15 days. By the age of four to six weeks, when their milk teeth are fully functional, the pups are given small food items such as mice, rabbits, or pieces of ungulate carcasses, with lactation steadily decreasing after two months. [22] Unlike wolf pups, coyote pups begin seriously fighting (as opposed to play fighting) prior to engaging in play behavior. A common play behavior includes the coyote "hip-slam". [74] By three weeks of age, coyote pups bite each other with less inhibition than wolf pups. By the age of four to five weeks, pups have established dominance hierarchies, and are by then more likely to play rather than fight. [87] The male plays an active role in feeding, grooming, and guarding the pups, but abandons them if the female goes missing before the pups are completely weaned. The den is abandoned by June to July, and the pups follow their parents in patrolling their territory and hunting. Pups may leave their families in August, though can remain for much longer. The pups attain adult dimensions at eight months and gain adult weight a month later. [22]

    Territorial and sheltering behaviors Edit

    Individual feeding territories vary in size from 0.4 to 62 km 2 (0.15 to 24 sq mi), with the general concentration of coyotes in a given area depending on food abundance, adequate denning sites, and competition with conspecifics and other predators. The coyote generally does not defend its territory outside of the denning season, [22] and is much less aggressive towards intruders than the wolf is, typically chasing and sparring with them, but rarely killing them. [88] Conflicts between coyotes can arise during times of food shortage. [22] Coyotes mark their territories by raised-leg urination and ground-scratching. [89] [84]

    Like wolves, coyotes use a den (usually the deserted holes of other species) when gestating and rearing young, though they may occasionally give birth under sagebrushes in the open. Coyote dens can be located in canyons, washouts, coulees, banks, rock bluffs, or level ground. Some dens have been found under abandoned homestead shacks, grain bins, drainage pipes, railroad tracks, hollow logs, thickets, and thistles. The den is continuously dug and cleaned out by the female until the pups are born. Should the den be disturbed or infested with fleas, the pups are moved into another den. A coyote den can have several entrances and passages branching out from the main chamber. [90] A single den can be used year after year. [23]

    Hunting and feeding behaviors Edit

    While the popular consensus is that olfaction is very important for hunting, [91] two studies that experimentally investigated the role of olfactory, auditory, and visual cues found that visual cues are the most important ones for hunting in red foxes [92] and coyotes. [93] [94]

    When hunting large prey, the coyote often works in pairs or small groups. [5] Success in killing large ungulates depends on factors such as snow depth and crust density. Younger animals usually avoid participating in such hunts, with the breeding pair typically doing most of the work. [23] Unlike the wolf, which attacks large prey from the rear, the coyote approaches from the front, lacerating its prey's head and throat. Like other canids, the coyote caches excess food. [95] Coyotes catch mouse-sized rodents by pouncing, whereas ground squirrels are chased. Although coyotes can live in large groups, small prey is typically caught singly. [23] Coyotes have been observed to kill porcupines in pairs, using their paws to flip the rodents on their backs, then attacking the soft underbelly. Only old and experienced coyotes can successfully prey on porcupines, with many predation attempts by young coyotes resulting in them being injured by their prey's quills. [96] Coyotes sometimes urinate on their food, possibly to claim ownership over it. [89] [97] Recent evidence demonstrates that at least some coyotes have become more nocturnal in hunting, presumably to avoid humans. [98] [ scientific citation needed ]

    Coyotes may occasionally form mutualistic hunting relationships with American badgers, assisting each other in digging up rodent prey. [99] The relationship between the two species may occasionally border on apparent "friendship", as some coyotes have been observed laying their heads on their badger companions or licking their faces without protest. The amicable interactions between coyotes and badgers were known to pre-Columbian civilizations, as shown on a Mexican jar dated to 1250–1300 CE depicting the relationship between the two. [100]

    Food scraps, pet food, and animal feces may attract a coyote to a trash can. [101]

    Communication Edit

    Body language Edit

    Being both a gregarious and solitary animal, the variability of the coyote's visual and vocal repertoire is intermediate between that of the solitary foxes and the highly social wolf. [81] The aggressive behavior of the coyote bears more similarities to that of foxes than it does that of wolves and dogs. An aggressive coyote arches its back and lowers its tail. [102] Unlike dogs, which solicit playful behavior by performing a "play-bow" followed by a "play-leap", play in coyotes consists of a bow, followed by side-to-side head flexions and a series of "spins" and "dives". Although coyotes will sometimes bite their playmates' scruff as dogs do, they typically approach low, and make upward-directed bites. [103] Pups fight each other regardless of sex, while among adults, aggression is typically reserved for members of the same sex. Combatants approach each other waving their tails and snarling with their jaws open, though fights are typically silent. Males tend to fight in a vertical stance, while females fight on all four paws. Fights among females tend to be more serious than ones among males, as females seize their opponents' forelegs, throat, and shoulders. [102]

    Vocalizations Edit

    The coyote has been described as "the most vocal of all [wild] North American mammals". [104] [105] Its loudness and range of vocalizations was the cause for its binomial name Canis latrans, meaning "barking dog". At least 11 different vocalizations are known in adult coyotes. These sounds are divided into three categories: agonistic and alarm, greeting, and contact. Vocalizations of the first category include woofs, growls, huffs, barks, bark howls, yelps, and high-frequency whines. Woofs are used as low-intensity threats or alarms and are usually heard near den sites, prompting the pups to immediately retreat into their burrows. Growls are used as threats at short distances but have also been heard among pups playing and copulating males. Huffs are high-intensity threat vocalizations produced by rapid expiration of air. Barks can be classed as both long-distance threat vocalizations and alarm calls. Bark howls may serve similar functions. Yelps are emitted as a sign of submission, while high-frequency whines are produced by dominant animals acknowledging the submission of subordinates. Greeting vocalizations include low-frequency whines, 'wow-oo-wows', and group yip howls. Low-frequency whines are emitted by submissive animals and are usually accompanied by tail wagging and muzzle nibbling. The sound known as 'wow-oo-wow' has been described as a "greeting song". The group yip howl is emitted when two or more pack members reunite and may be the final act of a complex greeting ceremony. Contact calls include lone howls and group howls, as well as the previously mentioned group yip howls. The lone howl is the most iconic sound of the coyote and may serve the purpose of announcing the presence of a lone individual separated from its pack. Group howls are used as both substitute group yip howls and as responses to either lone howls, group howls, or group yip howls. [24]

    Habitat Edit

    Prior to the near extermination of wolves and cougars, the coyote was most numerous in grasslands inhabited by bison, pronghorn, elk, and other deer, doing particularly well in short-grass areas with prairie dogs, though it was just as much at home in semiarid areas with sagebrush and jackrabbits or in deserts inhabited by cactus, kangaroo rats, and rattlesnakes. As long as it was not in direct competition with the wolf, the coyote ranged from the Sonoran Desert to the alpine regions of adjoining mountains or the plains and mountainous areas of Alberta. With the extermination of the wolf, the coyote's range expanded to encompass broken forests from the tropics of Guatemala and the northern slope of Alaska. [22]

    Coyotes walk around 5–16 kilometres (3–10 mi) per day, often along trails such as logging roads and paths they may use iced-over rivers as travel routes in winter. They are often crepuscular, being more active around evening and the beginning of the night than during the day. Like many canids, coyotes are competent swimmers, reported to be able to travel at least 0.8 kilometres (0.5 mi) across water. [106]

    Diet Edit

    The coyote is ecologically the North American equivalent of the Eurasian golden jackal. [107] Likewise, the coyote is highly versatile in its choice of food, but is primarily carnivorous, with 90% of its diet consisting of meat. Prey species include bison (largely as carrion), white-tailed deer, mule deer, moose, elk, bighorn sheep, pronghorn, rabbits, hares, rodents, birds (especially galliformes, young water birds and pigeons and doves), amphibians (except toads), lizards, snakes, turtles and tortoises, fish, crustaceans, and insects. Coyotes may be picky over the prey they target, as animals such as shrews, moles, and brown rats do not occur in their diet in proportion to their numbers. [22] However, terrestrial and/or burrowing small mammals such as ground squirrels and associated species (marmots, prairie dogs, chipmunks) as well as voles, pocket gophers, kangaroo rats and other ground-favoring rodents may be quite common foods, especially for lone coyotes. [108] [109] [110] More unusual prey include fishers, [111] young black bear cubs, [112] harp seals [113] and rattlesnakes. Coyotes kill rattlesnakes mostly for food (but also to protect their pups at their dens) by teasing the snakes until they stretch out and then biting their heads and snapping and shaking the snakes. [114] Birds taken by coyotes may range in size from thrashers, larks and sparrows to adult wild turkeys and, possibly, brooding adult swans and pelicans. [115] [116] [117] [118] If working in packs or pairs, coyotes may have access to larger prey than lone individuals normally take, such as various prey weighing more than 10 kg (22 lb). [119] [120] In some cases, packs of coyotes have dispatched much larger prey such as adult Odocoileus deer, cow elk, pronghorns and wild sheep, although the young fawn, calves and lambs of these animals are considerably more often taken even by packs, as well as domestic sheep and domestic cattle. In some cases, coyotes can bring down prey weighing up to 100 to 200 kg (220 to 440 lb) or more. When it comes to adult ungulates such as wild deer, they often exploit them when vulnerable such as those that are infirm, stuck in snow or ice, otherwise winter-weakened or heavily pregnant, whereas less wary domestic ungulates may be more easily exploited. [119] [121] [122] [123] [124] [125] [126]

    Although coyotes prefer fresh meat, they will scavenge when the opportunity presents itself. Excluding the insects, fruit, and grass eaten, the coyote requires an estimated 600 g (1.3 lb) of food daily, or 250 kg (550 lb) annually. [22] The coyote readily cannibalizes the carcasses of conspecifics, with coyote fat having been successfully used by coyote hunters as a lure or poisoned bait. [7] The coyote's winter diet consists mainly of large ungulate carcasses, with very little plant matter. Rodent prey increases in importance during the spring, summer, and fall. [5]

    The coyote feeds on a variety of different produce, including blackberries, blueberries, peaches, pears, apples, prickly pears, chapotes, persimmons, peanuts, watermelons, cantaloupes, and carrots. During the winter and early spring, the coyote eats large quantities of grass, such as green wheat blades. It sometimes eats unusual items such as cotton cake, soybean meal, domestic animal droppings, beans, and cultivated grain such as maize, wheat, and sorghum. [22]

    In coastal California, coyotes now consume a higher percentage of marine-based food than their ancestors, which is thought to be due to the extirpation of the grizzly bear from this region. [127] In Death Valley, coyotes may consume great quantities of hawkmoth caterpillars or beetles in the spring flowering months. [128]

    Enemies and competitors Edit

    In areas where the ranges of coyotes and gray wolves overlap, interference competition and predation by wolves has been hypothesized to limit local coyote densities. Coyote ranges expanded during the 19th and 20th centuries following the extirpation of wolves, while coyotes were driven to extinction on Isle Royale after wolves colonized the island in the 1940s. One study conducted in Yellowstone National Park, where both species coexist, concluded that the coyote population in the Lamar River Valley declined by 39% following the reintroduction of wolves in the 1990s, while coyote populations in wolf inhabited areas of the Grand Teton National Park are 33% lower than in areas where they are absent. [129] [130] Wolves have been observed to not tolerate coyotes in their vicinity, though coyotes have been known to trail wolves to feed on their kills. [100]

    Coyotes may compete with cougars in some areas. In the eastern Sierra Nevada, coyotes compete with cougars over mule deer. Cougars normally outcompete and dominate coyotes, and may kill them occasionally, thus reducing coyote predation pressure on smaller carnivores such as foxes and bobcats. [131] Coyotes that are killed are sometimes not eaten, perhaps indicating that these comprise competitive interspecies interactions, however there are multiple confirmed cases of cougars also eating coyotes. [132] [133] In northeastern Mexico, cougar predation on coyotes continues apace but coyotes were absent from the prey spectrum of sympatric jaguars, apparently due to differing habitat usages. [134]

    Other than by gray wolves and cougars, predation on adult coyotes is relatively rare but multiple other predators can be occasional threats. In some cases, adult coyotes have been preyed upon by both American black and grizzly bears, [135] American alligators, [136] large Canada lynx [137] and golden eagles. [138] At kill sites and carrion, coyotes, especially if working alone, tend to be dominated by wolves, cougars, bears, wolverines and, usually but not always, eagles (i.e., bald and golden). When such larger, more powerful and/or more aggressive predators such as these come to a shared feeding site, a coyote may either try to fight, wait until the other predator is done or occasionally share a kill, but if a major danger such as wolves or an adult cougar is present, the coyote will tend to flee. [139] [140] [141] [142] [143] [144] [145] [146]

    Coyotes rarely kill healthy adult red foxes, and have been observed to feed or den alongside them, though they often kill foxes caught in traps. Coyotes may kill fox kits, but this is not a major source of mortality. [147] In southern California, coyotes frequently kill gray foxes, and these smaller canids tend to avoid areas with high coyote densities. [148]

    In some areas, coyotes share their ranges with bobcats. These two similarly-sized species rarely physically confront one another, though bobcat populations tend to diminish in areas with high coyote densities. [149] However, several studies have demonstrated interference competition between coyotes and bobcats, and in all cases coyotes dominated the interaction. [150] [151] Multiple researchers [152] [153] [154] [151] [155] reported instances of coyotes killing bobcats, whereas bobcats killing coyotes is more rare. [150] Coyotes attack bobcats using a bite-and-shake method similar to what is used on medium-sized prey. Coyotes (both single individuals and groups) have been known to occasionally kill bobcats – in most cases, the bobcats were relatively small specimens, such as adult females and juveniles. [151] However, coyote attacks (by an unknown number of coyotes) on adult male bobcats have occurred. In California, coyote and bobcat populations are not negatively correlated across different habitat types, but predation by coyotes is an important source of mortality in bobcats. [148] Biologist Stanley Paul Young noted that in his entire trapping career, he had never successfully saved a captured bobcat from being killed by coyotes, and wrote of two incidents wherein coyotes chased bobcats up trees. [100] Coyotes have been documented to directly kill Canada lynx on occasion, [156] [157] [158] and compete with them for prey, especially snowshoe hares. [156] In some areas, including central Alberta, lynx are more abundant where coyotes are few, thus interactions with coyotes appears to influence lynx populations more than the availability of snowshoe hares. [159]

    Due to the coyote's wide range and abundance throughout North America, it is listed as Least Concern by the International Union for Conservation of Nature (IUCN). [2] The coyote's pre-Columbian range was limited to the Southwest and Plains regions of North America, and northern and central Mexico. By the 19th century, the species expanded north and east, expanding further after 1900, coinciding with land conversion and the extirpation of wolves. By this time, its range encompassed the entire North American continent, including all of the contiguous United States and Mexico, southward into Central America, and northward into most of Canada and Alaska. [161] This expansion is ongoing, and the species now occupies the majority of areas between 8°N (Panama) and 70°N (northern Alaska). [2]

    Although it was once widely believed that coyotes are recent immigrants to southern Mexico and Central America, aided in their expansion by deforestation, Pleistocene and Early Holocene records, as well as records from the pre-Columbian period and early European colonization show that the animal was present in the area long before modern times. Nevertheless, range expansion did occur south of Costa Rica during the late 1970s and northern Panama in the early 1980s, following the expansion of cattle-grazing lands into tropical rain forests. The coyote is predicted to appear in northern Belize in the near future, as the habitat there is favorable to the species. [162] Concerns have been raised of a possible expansion into South America through the Panamanian Isthmus, should the Darién Gap ever be closed by the Pan-American Highway. [163] This fear was partially confirmed in January 2013, when the species was recorded in eastern Panama's Chepo District, beyond the Panama Canal. [64]

    A 2017 genetic study proposes that coyotes were originally not found in the area of the eastern United States. From the 1890s, dense forests were transformed into agricultural land and wolf control implemented on a large scale, leaving a niche for coyotes to disperse into. There were two major dispersals from two populations of genetically distinct coyotes. The first major dispersal to the northeast came in the early 20th century from those coyotes living in the northern Great Plains. These came to New England via the northern Great Lakes region and southern Canada, and to Pennsylvania via the southern Great Lakes region, meeting together in the 1940s in New York and Pennsylvania. These coyotes have hybridized with the remnant gray wolf and eastern wolf populations, which has added to coyote genetic diversity and may have assisted adaptation to the new niche. The second major dispersal to the southeast came in the mid-20th century from Texas and reached the Carolinas in the 1980s. These coyotes have hybridized with the remnant red wolf populations before the 1970s when the red wolf was extirpated in the wild, which has also added to coyote genetic diversity and may have assisted adaptation to this new niche as well. Both of these two major coyote dispersals have experienced rapid population growth and are forecast to meet along the mid-Atlantic coast. The study concludes that for coyotes the long range dispersal, gene flow from local populations, and rapid population growth may be inter-related. [164]

    In July 2018 Cambridge, Ontario city government removed leg traps from a city park after complaints about perceived harm to the coyotes. [165] [166]

    Among large North American carnivores, the coyote probably carries the largest number of diseases and parasites, likely due to its wide range and varied diet. [167] Viral diseases known to infect coyotes include rabies, canine distemper, infectious canine hepatitis, four strains of equine encephalitis, and oral papillomatosis. By the late 1970s, serious rabies outbreaks in coyotes had ceased to be a problem for over 60 years, though sporadic cases every 1–5 years did occur. Distemper causes the deaths of many pups in the wild, though some specimens can survive infection. Tularemia, a bacterial disease, infects coyotes from tick bites and through their rodent and lagomorph prey, and can be deadly for pups. [168]

    Coyotes can be infected by both demodectic and sarcoptic mange, the latter being the most common. Mite infestations are rare and incidental in coyotes, while tick infestations are more common, with seasonal peaks depending on locality (May–August in the Northwest, March–November in Arkansas). Coyotes are only rarely infested with lice, while fleas infest coyotes from puphood, though they may be more a source of irritation than serious illness. Pulex simulans is the most common species to infest coyotes, while Ctenocephalides canis tends to occur only in places where coyotes and dogs (its primary host) inhabit the same area. Although coyotes are rarely host to flukes, they can nevertheless have serious effects on coyotes, particularly Nanophyetus salmincola, which can infect them with salmon poisoning disease, a disease with a 90% mortality rate. Trematode Metorchis conjunctus can also infect coyotes. [169] Tapeworms have been recorded to infest 60–95% of all coyotes examined. The most common species to infest coyotes are Taenia pisiformis and Taenia crassiceps, which uses cottontail rabbits as intermediate hosts. The largest species known in coyotes is T. hydatigena, which enters coyotes through infected ungulates, and can grow to lengths of 80 to 400 cm (31 to 157 in). Although once largely limited to wolves, Echinococcus granulosus has expanded to coyotes since the latter began colonizing former wolf ranges. The most frequent ascaroid roundworm in coyotes is Toxascaris leonina, which dwells in the coyote's small intestine and has no ill effects, except for causing the host to eat more frequently. Hookworms of the genus Ancylostoma infest coyotes throughout their range, being particularly prevalent in humid areas. In areas of high moisture, such as coastal Texas, coyotes can carry up to 250 hookworms each. The blood-drinking A. caninum is particularly dangerous, as it damages the coyote through blood loss and lung congestion. A 10-day-old pup can die from being host to as few as 25 A. caninum worms. [168]

    In folklore and mythology Edit

    Coyote features as a trickster figure and skin-walker in the folktales of some Native Americans, notably several nations in the Southwestern and Plains regions, where he alternately assumes the form of an actual coyote or that of a man. As with other trickster figures, Coyote acts as a picaresque hero who rebels against social convention through deception and humor. [170] Folklorists such as Harris believe coyotes came to be seen as tricksters due to the animal's intelligence and adaptability. [171] After the European colonization of the Americas, Anglo-American depictions of Coyote are of a cowardly and untrustworthy animal. [172] Unlike the gray wolf, which has undergone a radical improvement of its public image, Anglo-American cultural attitudes towards the coyote remain largely negative. [173]

    In the Maidu creation story, Coyote introduces work, suffering, and death to the world. Zuni lore has Coyote bringing winter into the world by stealing light from the kachinas. The Chinook, Maidu, Pawnee, Tohono O'odham, and Ute portray the coyote as the companion of The Creator. A Tohono O'odham flood story has Coyote helping Montezuma survive a global deluge that destroys humanity. After The Creator creates humanity, Coyote and Montezuma teach people how to live. The Crow creation story portrays Old Man Coyote as The Creator. In The Dineh creation story, Coyote was present in the First World with First Man and First Woman, though a different version has it being created in the Fourth World. The Navajo Coyote brings death into the world, explaining that without death, too many people would exist, thus no room to plant corn. [174]

    Prior to the Spanish conquest of the Aztec Empire, Coyote played a significant role in Mesoamerican cosmology. The coyote symbolized military might in Classic era Teotihuacan, with warriors dressing up in coyote costumes to call upon its predatory power. The species continued to be linked to Central Mexican warrior cults in the centuries leading up to the post-Classic Aztec rule. [175] In Aztec mythology, Huehuecóyotl (meaning "old coyote"), the god of dance, music and carnality, is depicted in several codices as a man with a coyote's head. [176] He is sometimes depicted as a womanizer, responsible for bringing war into the world by seducing Xochiquetzal, the goddess of love. [177] Epigrapher David H. Kelley argued that the god Quetzalcoatl owed its origins to pre-Aztec Uto-Aztecan mythological depictions of the coyote, which is portrayed as mankind's "Elder Brother", a creator, seducer, trickster, and culture hero linked to the morning star. [178]

    Attacks on humans Edit

    Coyote attacks on humans are uncommon and rarely cause serious injuries, due to the relatively small size of the coyote, but have been increasingly frequent, especially in California. There have been only two confirmed fatal attacks: one on a three-year-old named Kelly Keen in Glendale, California [179] and another on a nineteen-year-old named Taylor Mitchell in Nova Scotia, Canada. [180] In the 30 years leading up to March 2006, at least 160 attacks occurred in the United States, mostly in the Los Angeles County area. [181] Data from United States Department of Agriculture (USDA) Wildlife Services, the California Department of Fish and Game, and other sources show that while 41 attacks occurred during the period of 1988–1997, 48 attacks were verified from 1998 through 2003. The majority of these incidents occurred in Southern California near the suburban-wildland interface. [179]

    In the absence of the harassment of coyotes practiced by rural people, urban coyotes are losing their fear of humans, which is further worsened by people intentionally or unintentionally feeding coyotes. In such situations, some coyotes have begun to act aggressively toward humans, chasing joggers and bicyclists, confronting people walking their dogs, and stalking small children. [179] Non-rabid coyotes in these areas sometimes target small children, mostly under the age of 10, though some adults have been bitten. [182]

    Although media reports of such attacks generally identify the animals in question as simply "coyotes", research into the genetics of the eastern coyote indicates those involved in attacks in northeast North America, including Pennsylvania, New York, New England, and eastern Canada, may have actually been coywolves, hybrids of Canis latrans and C. lupus, not fully coyotes. [183]

    Livestock and pet predation Edit

    As of 2007 [update] , coyotes were the most abundant livestock predators in western North America, causing the majority of sheep, goat, and cattle losses. [184] For example, according to the National Agricultural Statistics Service, coyotes were responsible for 60.5% of the 224,000 sheep deaths attributed to predation in 2004. [185] [186] [ failed verification ] The total number of sheep deaths in 2004 comprised 2.22% of the total sheep and lamb population in the United States, [187] which, according to the National Agricultural Statistics Service USDA report, totaled 4.66 million and 7.80 million heads respectively as of July 1, 2005. [188] Because coyote populations are typically many times greater and more widely distributed than those of wolves, coyotes cause more overall predation losses. United States government agents routinely shoot, poison, trap, and kill about 90,000 coyotes each year to protect livestock. [189] An Idaho census taken in 2005 showed that individual coyotes were 5% as likely to attack livestock as individual wolves. [190] In Utah, more than 11,000 coyotes were killed for bounties totaling over $500,000 in the fiscal year ending June 30, 2017. [191]

    Livestock guardian dogs are commonly used to aggressively repel predators and have worked well in both fenced pasture and range operations. [192] A 1986 survey of sheep producers in the USA found that 82% reported the use of dogs represented an economic asset. [193]

    Re-wilding cattle, which involves increasing the natural protective tendencies of cattle, is a method for controlling coyotes discussed by Temple Grandin of Colorado State University. [194] This method is gaining popularity among producers who allow their herds to calve on the range and whose cattle graze open pastures throughout the year. [195]

    Coyotes typically bite the throat just behind the jaw and below the ear when attacking adult sheep or goats, with death commonly resulting from suffocation. Blood loss is usually a secondary cause of death. Calves and heavily fleeced sheep are killed by attacking the flanks or hindquarters, causing shock and blood loss. When attacking smaller prey, such as young lambs, the kill is made by biting the skull and spinal regions, causing massive tissue and bone damage. Small or young prey may be completely carried off, leaving only blood as evidence of a kill. Coyotes usually leave the hide and most of the skeleton of larger animals relatively intact, unless food is scarce, in which case they may leave only the largest bones. Scattered bits of wool, skin, and other parts are characteristic where coyotes feed extensively on larger carcasses. [184]

    Tracks are an important factor in distinguishing coyote from dog predation. Coyote tracks tend to be more oval-shaped and compact than those of domestic dogs, and their claw marks are less prominent and the tracks tend to follow a straight line more closely than those of dogs. With the exception of sighthounds, most dogs of similar weight to coyotes have a slightly shorter stride. [184] Coyote kills can be distinguished from wolf kills by less damage to the underlying tissues in the former. Also, coyote scat tends to be smaller than wolf scat. [196] [197]

    Coyotes are often attracted to dog food and animals that are small enough to appear as prey. Items such as garbage, pet food, and sometimes feeding stations for birds and squirrels attract coyotes into backyards. About three to five pets attacked by coyotes are brought into the Animal Urgent Care hospital of South Orange County (California) each week, the majority of which are dogs, since cats typically do not survive the attacks. [198] Scat analysis collected near Claremont, California, revealed that coyotes relied heavily on pets as a food source in winter and spring. [179] At one location in Southern California, coyotes began relying on a colony of feral cats as a food source. Over time, the coyotes killed most of the cats and then continued to eat the cat food placed daily at the colony site by people who were maintaining the cat colony. [179] Coyotes usually attack smaller-sized dogs, but they have been known to attack even large, powerful breeds such as the Rottweiler in exceptional cases. [199] Dogs larger than coyotes, such as greyhounds, are generally able to drive them off and have been known to kill coyotes. [200] Smaller breeds are more likely to suffer injury or death. [182]

    Hunting Edit

    Coyote hunting is one of the most common forms of predator hunting that humans partake in. There are not many regulations with regard to the taking of the coyote which means there are many different methods that can be used to hunt the animal. The most common forms are trapping, calling, and hound hunting. [201] Since coyotes are colorblind, seeing only in shades of gray and subtle blues, open camouflages, and plain patterns can be used. The average male coyote weighs 8 to 20 kg (18 to 44 lbs) and the average female coyote 7 to 18 kg (15 to 40 lbs) a universal projectile that can perform between those weights is the .223 Remington so that the projectile expands in the target after the entry but before the exit thus delivering the most energy. [202] Coyotes being the light and agile animals they are, they often leave a very light impression on terrain. The coyote's footprint is oblong, approximately 6.35 cm (2.5-inches) long and 5.08 cm (2-inches) wide. There are 4 claws in both their front and hind paws. The coyote's center pad is relatively shaped like that of a rounded triangle. Like the domestic dog the coyote's front paw is slightly larger than the hind paw. The coyote's paw is most similar to that of the domestic dog. [203]

    Uses Edit

    Prior to the mid-19th century, coyote fur was considered worthless. This changed with the diminution of beavers, and by 1860, the hunting of coyotes for their fur became a great source of income (75 cents to $1.50 per skin) for wolfers in the Great Plains. Coyote pelts were of significant economic importance during the early 1950s, ranging in price from $5 to $25 per pelt, depending on locality. [204] The coyote's fur is not durable enough to make rugs, [205] but can be used for coats and jackets, scarves, or muffs. The majority of pelts are used for making trimmings, such as coat collars and sleeves for women's clothing. Coyote fur is sometimes dyed black as imitation silver fox. [204]

    Coyotes were occasionally eaten by trappers and mountain men during the western expansion. Coyotes sometimes featured in the feasts of the Plains Indians, and coyote pups were eaten by the indigenous people of San Gabriel, California. The taste of coyote meat has been likened to that of the wolf and is more tender than pork when boiled. Coyote fat, when taken in the fall, has been used on occasion to grease leather or eaten as a spread. [206]

    Tameability Edit

    Coyotes were likely semidomesticated by various pre-Columbian cultures. Some 19th-century writers wrote of coyotes being kept in native villages in the Great Plains. The coyote is easily tamed as a pup, but can become destructive as an adult. [207] Both full-blooded and hybrid coyotes can be playful and confiding with their owners, but are suspicious and shy of strangers, [72] though coyotes being tractable enough to be used for practical purposes like retrieving [208] and pointing have been recorded. [209] A tame coyote named "Butch", caught in the summer of 1945, had a short-lived career in cinema, appearing in Smoky and Ramrod before being shot while raiding a henhouse. [207]


    Contents

    The binomial name Crocodylus niloticus is derived from the Greek κρόκη, kroke ("pebble"), δρῖλος, drilos ("worm"), referring to its rough skin and niloticus, meaning "from the Nile River". The Nile crocodile is called tanin ha-yeor in Hebrew, [13] timsah al-nil in Arabic, mamba in Swahili, garwe in Shona, ngwenya in Ndebele, ngwena in Venda, and kwena in Sotho and Tswana. It also sometimes referred to as the African crocodile, Ethiopian crocodile, common crocodile, or the black crocodile. [8] [14] [15]

    Although no subspecies are currently formally recognized, as many as seven have been proposed, mostly due to variations in appearance and size noted in various populations through Africa. These have consisted of: C. n. africanus (informally named the East African Nile crocodile), C. n. chamses (the West African Nile crocodile), C. n. cowiei (the South African Nile crocodile), C. n. madagascariensis (the Malagasy or Madagascar Nile crocodile, regionally also known as the croco Mada, which translates to Malagasy crocodile), C. n. niloticus (the Ethiopian Nile crocodile, this would be the nominate subspecies), C. n. pauciscutatus (the Kenyan Nile crocodile) and C. (n.) suchus (now widely perceived by crocodilian biologists as a separate species). [16] [17] In a study of the morphology of the various populations, including C. (n.) suchus, the appearance of the Nile crocodile sensu lato was found to be more variable than any other currently recognized crocodile species, and at least some of these variations were related to locality. [18]

    A study on Lake Turkana in Kenya (informally this population would be placed in C. n. pauciscutatus) has shown that the local crocodiles appear to have more osteoderms in their ventral surface than other known populations, thus are of lesser value in leather trading, accounting for an exceptionally large (possibly overpopulated) local population there in the late 20th century. [19] The segregation of the West African crocodile (C. suchus) from the Nile crocodile has been supported by morphological characteristics, [18] [20] studies of genetic materials [17] [20] and habitat preferences. [21] The separation of the two is not recognized by the IUCN as their last evaluations of the group was in 2008 and 2009, [1] [22] years before the primary publications supporting the distinctiveness of the West African crocodiles. [18] [20] [21]

    Although originally thought to be the same species as the West African crocodile, genetic studies using DNA sequencing have revealed that the Nile crocodile is actually more closely related to the crocodiles of the Americas, namely the American (C. acutus), Cuban (C. rhombifer), Morelet's (C. moreletii), and Orinoco crocodiles (C. intermedius). [20] [23] [24] [25] [26] [27] The fossil species C. checchiai from the Miocene in Kenya was about the same size as the modern Nile crocodiles and shared similar physical characteristics to the modern species, [23] [24] [28] and analysis of C. checchiai supports their close relationship and the theory of the Nile crocodile being the base of the evolutionary radiation of the New World crocodiles. [29] Dispersal across the Atlantic from Africa is thought to have occurred 5 to 6 million years ago. [30] [31]

    At one time, the fossil species Rimasuchus lloydi was thought to be the ancestor of the Nile crocodile, but more recent research has indicated that Rimasuchus, despite its very large size (about 20–30% bigger than a Nile crocodile with a skull length estimated up to 97 cm (38 in)), is more closely related to the dwarf crocodile (Osteolaemus tetraspis) among living species. [19] [23] Two other fossil species from Africa retained in the genus Crocodylus appear to be closely related to the Nile crocodile: C. anthropophagus from Plio-Pleistocene Tanzania and C. thorbjarnarsoni from Plio-Pleistocene Kenya. C. anthropophagus and C. thorbjarnarsoni were both somewhat larger, with projected total lengths up to 7.5–7.6 m (24 ft 7 in–24 ft 11 in). [23] [24] [28] As well as being larger, C. anthropophagus and C. thorbjarnarsoni, as well as Rimasuchus spp., were all relatively broad-snouted, indicating a specialization at hunting sizeable prey, such as large mammals and freshwater turtles, the latter much larger than any in present-day Africa. [23] [24] Studies have since shown these other African crocodiles to be only more distantly related to the Nile crocodile. [26] [27]

    Below is a cladogram based on a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data, [26] as revised by the 2021 Hekkala et al. paleogenomics study using DNA extracted from the extinct Voay. [27]

    Crocodylus Tirari Desert†

    Crocodylus novaeguineae New Guinea crocodile

    Crocodylus intermedius Orinoco crocodile

    Adult Nile crocodiles have a dark bronze colouration above, with faded blackish spots and stripes variably appearing across the back and a dingy off-yellow on the belly, although mud can often obscure the crocodile's actual colour. [14] The flanks, which are yellowish-green in colour, have dark patches arranged in oblique stripes in highly variable patterns. Some variation occurs relative to environment specimens from swift-flowing waters tend to be lighter in colour than those dwelling in murkier lakes or swamps, which provides camouflage that suits their environment, an example of clinal variation. Nile crocodiles have green eyes. [8] The colouration also helps to camouflage it juveniles are grey, multicoloured, or brown, with dark cross-bands on the tail and body. [32] The underbelly of young crocodiles is yellowish green. As it matures, Nile crocodiles become darker and the cross-bands fade, especially those on the upper-body. A similar tendency in coloration change during maturation has been noted in most crocodile species. [16] [33]

    Most morphological attributes of Nile crocodiles are typical of crocodilians as a whole. Like all crocodilians, for example, the Nile crocodile is a quadruped with four short, splayed legs, a long, powerful tail, a scaly hide with rows of ossified scutes running down its back and tail, and powerful, elongated jaws. [32] [34] Their skin has a number of poorly understood integumentary sense organs that may react to changes in water pressure, presumably allowing them to track prey movements in the water. [35] The Nile crocodile has fewer osteoderms on the belly, which are much more conspicuous on some of the more modestly sized crocodilians. The species, however, also has small, oval osteoderms on the sides of the body, as well as the throat. [33] [36] The Nile crocodile shares with all crocodilians a nictitating membrane to protect the eyes and lachrymal glands to cleanse its eyes with tears. The nostrils, eyes, and ears are situated on the top of the head, so the rest of the body can remain concealed under water. [34] [37] They have a four-chambered heart, although modified for their ectothermic nature due to an elongated cardiac septum, physiologically similar to the heart of a bird, which is especially efficient at oxygenating their blood. [38] [39] As in all crocodilians, Nile crocodiles have exceptionally high levels of lactic acid in their blood, which allows them to sit motionless in water for up to 2 hours. Levels of lactic acid as high as they are in a crocodile would kill most vertebrates. [16] However, exertion by crocodilians can lead to death due to increasing lactic acid to lethal levels, which in turn leads to failure of the animal's internal organs. This is rarely recorded in wild crocodiles, normally having been observed in cases where humans have mishandled crocodiles and put them through overly extended periods of physical struggling and stress. [9] [19]

    Skull and head morphology Edit

    The mouths of Nile crocodiles are filled with 64 to 68 sharply pointed, cone-shaped teeth (about a dozen less than alligators have). For most of a crocodile's life, broken teeth can be replaced. On each side of the mouth, five teeth are in the front of the upper jaw (premaxilla), 13 or 14 are in the rest of the upper jaw (maxilla), and 14 or 15 are on either side of the lower jaw (mandible). The enlarged fourth lower tooth fits into the notch on the upper jaw and is visible when the jaws are closed, as is the case with all true crocodiles. [9] [34] Hatchlings quickly lose a hardened piece of skin on the top of their mouths called the egg tooth, which they use to break through their eggshells at hatching. Among crocodilians, the Nile crocodile possesses a relatively long snout, which is about 1.6 to 2.0 times as long as broad at the level of the front corners of the eyes. [40] As is the saltwater crocodile, the Nile crocodile is considered a species with medium-width snout relative to other extant crocodilian species. [3]

    In a search for the largest crocodilian skulls in museums, the largest verifiable Nile crocodile skulls found were several housed in Arba Minch, Ethiopia, sourced from nearby Lake Chamo, which apparently included several specimens with a skull length more than 65 cm (26 in), with the largest one being 68.6 cm (27.0 in) in length with a mandibular length of 87 cm (34 in). Nile crocodiles with skulls this size are likely to measure in the range of 5.4 to 5.6 m (17 ft 9 in to 18 ft 4 in), which is also the length of the animals according to the museum where they were found. However, larger skulls may exist, as this study largely focused on crocodilians from Asia. [8] [41] The detached head of an exceptionally large Nile crocodile (killed in 1968 and measuring 5.87 m (19 ft 3 in) in length) was found to have weighed 166 kg (366 lb), including the large tendons used to shut the jaw. [7]

    Biting force Edit

    The bite force exerted by an adult Nile crocodile has been shown by Brady Barr to measure 22 kN (5,000 lbf). However, the muscles responsible for opening the mouth are exceptionally weak, allowing a person to easily hold them shut, and even larger crocodiles can be brought under control by the use of duct tape to bind the jaws together. [42] The broadest snouted modern crocodilians are alligators and larger caimans. For example, a 3.9 m (12 ft 10 in) black caiman (Melanosuchus niger) was found to have a notably broader and heavier skull than that of a Nile crocodile measuring 4.8 m (15 ft 9 in). [43] However, despite their robust skulls, alligators and caimans appear to be proportionately equal in biting force to true crocodiles, as the muscular tendons used to shut the jaws are similar in proportional size. Only the gharial (Gavialis gangeticus) (and perhaps some of the few very thin-snouted crocodilians) is likely to have noticeably diminished bite force compared to other living species due to its exceptionally narrow, fragile snout. More or less, the size of the tendons used to impart bite force increases with body size and the larger the crocodilian gets, the stronger its bite is likely to be. Therefore, a male saltwater crocodile, which had attained a length around 4.59 m (15 ft 1 in), was found to have the most powerful biting force ever tested in a lab setting for any type of animal. [44] [45]

    Size Edit

    The Nile crocodile is the largest crocodilian in Africa, and is generally considered the second-largest crocodilian after the saltwater crocodile. [8] Typical size has been reported to be as much as 4.5 to 5.5 m (14 ft 9 in to 18 ft 1 in), but this is excessive for actual average size per most studies and represents the upper limit of sizes attained by the largest animals in a majority of populations. [4] [32] [33] According to the Guinness Book of World Records, the typical mature size is between 3.4 and 3.7 m (11 ft 2 in and 12 ft 2 in), while Alexander and Marais (2007) state it is 2.8 to 3.5 m (9 ft 2 in to 11 ft 6 in) and Garrick and Lang (1977) claim from 3.0 to 4.5 m (9 ft 10 in to 14 ft 9 in). [5] [7] [10] According to Cott (1961), the average length and weight of Nile crocodiles from Uganda and Zambia in breeding maturity was 3.16 m (10 ft 4 in) and 137.5 kg (303 lb). [4] Per Graham (1968), the average length and weight of a large sample of adult crocodiles from Lake Turkana (formerly known as Lake Rudolf), Kenya was 3.66 m (12 ft 0 in) and body mass of 201.6 kg (444 lb). [46] Similarly, adult crocodiles from Kruger National Park reportedly average 3.65 m (12 ft 0 in) in length. [8] In comparison, the saltwater crocodile and gharial reportedly both average around 4 m (13 ft 1 in), so are about 30 cm (12 in) longer on average and the false gharial (Tomistoma schlegelii) may average about 3.75 m (12 ft 4 in), so may be slightly longer, as well. However, compared to the narrow-snouted, streamlined gharial and false gharial, the Nile crocodile is rather more robust and ranks second to the saltwater crocodile in total average body mass among living crocodilians, and is the considered to be the second largest reptile. [7] [46] [8] [33] The largest accurately measured male, shot near Mwanza, Tanzania, measured 6.45 m (21 ft 2 in) and weighed about 1,043–1,089 kg (2,300–2,400 lb). [7]

    Size and sexual dimorphism Edit

    Like all crocodiles, they are sexually dimorphic, with the males up to 30% larger than the females, though the difference is considerably less compared to some species, like the saltwater crocodile. Male Nile crocodiles are about 30 to 50 cm (12 to 20 in) longer on average at sexual maturity and grow more so than females after becoming sexually mature, especially expanding in bulk after exceeding 4 m (13 ft 1 in) in length. [32] [47] Adult male Nile crocodiles usually range in length from 3.3 to 5.0 m (10 ft 10 in to 16 ft 5 in) long at these lengths, an average sized male may weigh from 150 to 700 kg (330 to 1,540 lb). [4] [46] [48] [49] [50] In Limpopo, South Africa, males reportedly average 527 kg (1,162 lb). [6] Very old, mature ones can grow to 5.5 m (18 ft 1 in) or more in length (all specimens over 5.5 m (18 ft 1 in) from 1900 onward are cataloged later). [7] [8] [51] Mature female Nile crocodiles typically measure 2.2 to 3.8 m (7 ft 3 in to 12 ft 6 in), at which lengths the average female specimen would weigh 40 to 250 kg (88 to 551 lb). [4] [46] [32] [52]

    The bulk and mass of individual crocodiles can be fairly variable, some animals being relatively slender, while others being very robust females are often bulkier than males of a similar length. [4] [8] As an example of the body mass increase undergone by mature crocodiles, one of the larger crocodiles handled firsthand by Cott (1961) was 4.4 m (14 ft 5 in) and weighed 414.5 kg (914 lb), while the largest specimen measured by Graham and Beard (1973) was 4.8 m (15 ft 9 in) and weighed more than 680 kg (1,500 lb). [4] [7] [53] In attempts to parse the mean male and female lengths across the species, the mean adult length was estimated to be reportedly 4 m (13 ft 1 in) in males, at which males would average about 280 kg (620 lb) in weight, while that of the female is 3.05 m (10 ft 0 in), at which females would average about 116 kg (256 lb). [4] [46] [54] [55] This gives the Nile crocodile somewhat of a size advantage over the next largest non-marine predator on the African continent, the lion (Panthera leo), which averages 188 kg (414 lb) in males and 124 kg (273 lb) in females, and attains a maximum known weight of 313 kg (690 lb), far less than that of large male crocodiles. [7] [56]

    Evidence exists of Nile crocodiles from cooler climates, like the southern tip of Africa, being smaller, and may reach maximum lengths of only 4 m (13 ft 1 in). A smaller population from Mali, the Sahara Desert, and elsewhere in West Africa reaches only 2 to 3 m (6 ft 7 in to 9 ft 10 in) in length, [57] but it is now largely recognized as a separate species, the West African crocodile. [20]

    The Nile crocodile is presently the most common crocodilian in Africa, and is distributed throughout much of the continent. Among crocodilians today, only the saltwater crocodile occurs over a broader geographic area, [58] although other species, especially the spectacled caiman (Caiman crocodilus) (due to its small size and extreme adaptability in habitat and flexibility in diet), seem to actually be more abundant. [59] This species’ historic range, however, was even wider. They were found as far north as the Mediterranean coast in the Nile Delta and across the Red Sea in Palestine and Syria. The Nile crocodile has historically been recorded in areas where they are now regionally extinct. For example, Herodotus recorded the species inhabiting Lake Moeris in Egypt. They are thought to have become extinct in the Seychelles in the early 19th century (1810–1820). [8] [32] Today, Nile crocodiles are widely found in, among others, Somalia, Ethiopia, Uganda, Kenya, Egypt, the Central African Republic, the Democratic Republic of the Congo, Equatorial Guinea, Tanzania, Rwanda, Burundi, Zambia, Zimbabwe, Gabon, Angola, South Africa, Malawi, Mozambique, Namibia, Sudan, South Sudan, Botswana, and Cameroon. [22] The Nile crocodile's current range of distribution extends from the regional tributaries of the Nile in Sudan and Lake Nasser in Egypt to the Cunene of Angola, the Okavango Delta of Botswana, and the Olifants River in South Africa. [60]

    Isolated populations also exist in Madagascar, which likely colonized the island after the extinction of voay. [61] [62] In Madagascar, crocodiles occur in the western and southern parts from Sambirano to Tôlanaro. They have been spotted in Zanzibar and the Comoros in modern times, but occur very rarely. [8]

    The species was previously thought to extend in range into the whole of West and Central Africa, [63] [64] but these populations are now typically recognized as a distinct species, the West African (or desert) crocodile. [20] The distributional boundaries between these species were poorly understood, but following several studies, they are now better known. West African crocodiles are found throughout much of West and Central Africa, ranging east to South Sudan and Uganda where the species may come into contact with the Nile crocodile. Nile crocodiles are absent from most of West and Central Africa, but range into the latter region in eastern and southern Democratic Republic of Congo, and along the Central African coastal Atlantic region (as far north to Cameroon). [20] [65] Likely a level of habitat segregation occurs between the two species, but this remains to be confirmed. [21] [66]

    Nile crocodiles may be able to tolerate an extremely broad range of habitat types, including small brackish streams, fast-flowing rivers, swamps, dams, and tidal lakes and estuaries. [47] In East Africa, they are found mostly in rivers, lakes, marshes, and dams, favoring open, broad bodies of water over smaller ones. They are often found in waters adjacent to various open habitats such as savanna or even semi-desert but can also acclimate to well-wooded swamps, extensively wooded riparian zones, waterways of other woodlands and the perimeter of forests. [67] [68] [69] In Madagascar, the remnant population of Nile crocodiles has adapted to living within caves. [8] Nile crocodiles may make use of ephemeral watering holes on occasion. [70] Although not a regular sea-going species as is the American crocodile, and especially the saltwater crocodile, the Nile crocodile possesses salt glands like all true crocodiles (i.e., excluding alligators and caimans), and does on occasion enter coastal and even marine waters. [71] They have been known to enter the sea in some areas, with one specimen having been recorded 11 km (6.8 mi) off St. Lucia Bay in 1917. [4] [72]

    Invasive species Edit

    Nile crocodiles are an invasive species in North America, and several specimens have been recently captured in South Florida, though no signs that the population is reproducing in the wild have been found. [73] Genetic studies of Nile crocodiles captured in the wild in Florida have revealed that the specimens are all closely related to each other, suggesting a single source of the introduction. This source remains unclear, as their genetics do not match samples collected from captives at various zoos and theme parks in Florida. When compared to Nile crocodiles from their native Africa, the Florida wild specimens are most closely related to South African Nile crocodiles. [74] It is unknown how many Nile crocodiles are currently at large in Florida. [75] [76] The animals likely were either brought there to be released, or are escapees. [77]

    Generally, Nile crocodiles are relatively inert creatures, as are most crocodilians and other large, cold-blooded creatures. More than half of the crocodiles observed by Cott (1961), if not disturbed, spent the hours from 9:00 am to 4:00 pm continuously basking with their jaws open if conditions were sunny. If their jaws are bound together in the extreme midday heat, Nile crocodiles may easily die from overheating. [4] [78] Although they can remain practically motionless for hours on end, whether basking or sitting in shallows, Nile crocodiles are said to be constantly aware of their surroundings and aware of the presence of other animals. [8] However, mouth-gaping (while essential to thermoregulation) may also serve as a threat display to other crocodiles. For example, some specimens have been observed mouth-gaping at night, when overheating is not a risk. [11] In Lake Turkana, crocodiles rarely bask at all through the day, unlike crocodiles from most other areas, for unknown reasons, usually sitting motionless partially exposed at the surface in shallows with no apparent ill effect from the lack of basking on land. [53]

    In South Africa, Nile crocodiles are more easily observed in winter because of the extensive amount of time they spend basking at this time of year. More time is spent in water in overcast, rainy, or misty days. [79] In the southern reaches of their range, as a response to dry, cool conditions that they cannot survive externally, crocodiles may dig and take refuge in tunnels and engage in aestivation. [32] Pooley found in Royal Natal National Park that during aestivation, young crocodiles of 60 to 90 cm (24 to 35 in) total length would dig tunnels around 1.2 to 1.8 m (3 ft 11 in to 5 ft 11 in) in depth for most, some tunnels measuring more than 2.7 m (8 ft 10 in), the longest there being 3.65 m (12 ft 0 in). Crocodiles in aestivation are totally lethargic, entering a state similar to animals that hibernate. Only the largest individuals engaging in aestivation leave the burrow to sun on warmest days, otherwise these crocodiles rarely left their burrows. Aestivation has been recorded from May to August. [8] [32]

    Nile crocodiles usually dive for only a few minutes at a time, but can swim under water up to 30 minutes if threatened, and if they remain fully inactive, they can hold their breath for up to 2 hours (which, as aforementioned, is due to the high levels of lactic acid in their blood). [16] They have a rich vocal range, and good hearing. Nile crocodiles normally crawl along on their bellies, but they can also "high walk" with their trunks raised above the ground. Smaller specimens can gallop, and even larger individuals are capable on occasion of surprising bursts of speed, briefly reaching up to 14 km/h (8.7 mph). [4] [80] They can swim much faster by moving their bodies and tails in a sinuous fashion, and they can sustain this form of movement much longer than on land, with a maximum known swimming speed 30 to 35 km/h (19 to 22 mph), more than three times faster than any human. [81]

    Nile crocodiles have been widely known to have gastroliths in their stomachs, which are stones swallowed by animals for various purposes. Although this clearly is a deliberate behaviour for the species, the purpose is not definitively known. Gastroliths are not present in hatchlings, but increase quickly in presence within most crocodiles examined at 2–3.1 m (6 ft 7 in–10 ft 2 in) and yet normally become extremely rare again in very large specimens, meaning that some animals may eventually expel them. [4] [8] However, large specimens can have a large number of gastroliths. One crocodile measuring 3.84 m (12 ft 7 in) and weighing 239 kg (527 lb) had 5.1 kg (11 lb) of stones inside it, perhaps a record gastrolith weight for a crocodile. [4] Specimens shot near Mpondwe on the Semliki River had gastroliths in their stomach despite being shot miles away from any sources for stones, the same applies to the Kafue Flats, Upper Zambesi and Bangweulu Swamp, all of which often had stones inside them despite being nowhere near stony regions. Cott (1961) felt that gastroliths were most likely serving as ballast to provide stability and additional weight to sink in water, this bearing great probability over the theories that they assist in digestion and staving off hunger. [4] [8] However, Alderton (1998) stated that a study using radiology found that gastroliths were seen to internally aid the grinding of food during digestion for a small Nile crocodile. [19]

    Herodotus claimed that Nile crocodiles have a symbiotic relationship with certain birds, such as the Egyptian plover (Pluvianus aegyptius), which enter the crocodile's mouth and pick leeches feeding on the crocodile's blood, but no evidence of this interaction actually occurring in any crocodile species has been found, and it is most likely mythical or allegorical fiction. [82] However, Guggisberg (1972) had seen examples of birds picking scraps of meat from the teeth of basking crocodiles (without entering the mouth) and prey from soil very near basking crocodiles, so felt it was not impossible that a bold, hungry bird may occasionally nearly enter a crocodile's mouth, but not likely as a habitual behaviour. [8]

    Nile crocodiles are apex predators throughout their range. In the water, this species is an agile and rapid hunter relying on both movement and pressure sensors to catch any prey unfortunate enough to present itself inside or near the waterfront. [83] Out of water, however, the Nile crocodile can only rely on its limbs, as it gallops on solid ground, to chase prey. [84] No matter where they attack prey, this and other crocodilians take practically all of their food by ambush, needing to grab their prey in a matter of seconds to succeed. [8] They have an ectothermic metabolism, so can survive for long periods between meals—though when they do eat, they can eat up to half their body weight at a time. However, for such large animals, their stomachs are relatively small, not much larger than a basketball in an average-sized adult, so as a rule, they are anything but voracious eaters. [9] Young crocodiles feed more actively than their elders according to studies in Uganda and Zambia. In general, at the smallest sizes (0.3–1 m (1 ft 0 in–3 ft 3 in)), Nile crocodiles were most likely to have full stomachs (17.4% full per Cott) adults at 3–4 m (9 ft 10 in–13 ft 1 in) in length were most likely to have empty stomachs (20.2%). In the largest size range studied by Cott, 4–5 m (13 ft 1 in–16 ft 5 in), they were the second most likely to either have full stomachs (10%) or empty stomachs (20%). [4] Other studies have also shown a large number of adult Nile crocodiles with empty stomachs. For example, in Lake Turkana, Kenya, 48.4% of crocodiles had empty stomachs. [46] The stomachs of brooding females are always empty, meaning that they can survive several months without food. [8]

    The Nile crocodile mostly hunts within the confines of waterways, attacking aquatic prey or terrestrial animals when they come to the water to drink or to cross. [32] The crocodile mainly hunts land animals by almost fully submerging its body under water. Occasionally, a crocodile quietly surfaces so that only its eyes (to check positioning) and nostrils are visible, and swims quietly and stealthily toward its mark. The attack is sudden and unpredictable. The crocodile lunges its body out of water in practically the blink of an eye and grasps its prey. On other occasions, more of its head and upper body is visible, especially when the terrestrial prey animal is on higher ground, to get a sense of the direction of the prey item as the top of an embankment or on a tree branch. [8] Crocodile teeth are not used for tearing up flesh, but to sink deep into it and hold on to the prey item. The immense bite force, which may be as high as 5,000 lbf (22,000 N) in large adults, ensures that the prey item cannot escape through the grip. [85] Prey taken is often much smaller than the crocodile itself, and such prey can be overpowered and swallowed with ease. When it comes to larger prey, success depends on the crocodile's body power and weight to pull the prey item back into the water, where it is either drowned or killed by sudden thrashes of the head or by tearing it into pieces with the help of other crocodiles. [14]

    Subadult and smaller adult Nile crocodiles use their bodies and tails to herd groups of fish toward a bank, and eat them with quick sideways jerks of their heads. Some crocodiles of the species may habitually use their tails to sweep terrestrial prey off balance, sometimes forcing the prey specimen into the water, where it can be more easily drowned. [8] They also cooperate, blocking migrating fish by forming a semicircle across the river. [32] The most dominant crocodile eats first. Their ability to lie concealed with most of their bodies under water, combined with their speed over short distances, makes them effective opportunistic hunters of larger prey. They grab such prey in their powerful jaws, drag it into the water, and hold it underneath until it drowns. They also scavenge or steal kills from other predators, such as lions and leopards (Panthera pardus). [4] Groups of Nile crocodiles may travel hundreds of meters from a waterway to feast on a carcass. [32] They also feed on dead hippopotamuses (Hippopotamus amphibius) as a group (sometimes including three or four dozen crocodiles), tolerating each other. In fact, probably much of the food from crocodile stomachs may come from scavenging carrion, and the crocodiles could be viewed as performing a similar function at times as do vultures or hyenas on land. [8] Once their prey is dead, they rip off and swallow chunks of flesh. When groups are sharing a kill, they use each other for leverage, biting down hard and then twisting their bodies to tear off large pieces of meat in a "death roll". They may also get the necessary leverage by lodging their prey under branches or stones, before rolling and ripping. [8]

    The Nile crocodile possesses unique predation behavior characterized by the ability of preying both within its natural habitat and out of it, which often results in unpredicted attacks on almost any other animal up to twice its size. Most hunting on land is done at night by lying in ambush near forest trails or roadsides, up to 50 m (170 ft) from the water's edge. [86] Since their speed and agility on land is rather outmatched by most terrestrial animals, they must use obscuring vegetation or terrain to have a chance of succeeding during land-based hunts. [8] [86] In one case, an adult crocodile charged from the water up a bank to kill a bushbuck (Tragelaphus scriptus) and instead of dragging it into the water, was observed to pull the kill further on land into the cover of the bush. [87] Two subadult crocodiles were once seen carrying the carcass of a nyala (Tragelaphus angasii) across land in unison. [32] In South Africa, a game warden far from water sources in a savannah-scrub area reported that he saw a crocodile jump up and grab a donkey by the neck and then drag the prey off. [8] [88]

    Invertebrates Edit

    The type and size of the prey depends mostly on the size of the crocodile. [55] The diet of young crocodiles is made up largely of insects and other invertebrates, since this is the only prey the same animals can easily take. More than 100 species and genera of insects were identified among the food of crocodiles of this age. Of the insects taken there, beetles made up 58% of the diet, including Hydrophilus and Cybister. giant water bugs but also crickets and dragonflies. Arachnids such as Dolomedes water spiders are taken, but always secondarily to insects in Uganda and Zambia. [4] [89]

    Crabs are also largely taken by crocodiles under 1.5 m (4 ft 11 in), especially the genus Potamonautes, with different species being the primary crustacean food in different areas. Mollusks may occasionally be taken by young crocodiles (they are taken in larger numbers later in life in parts of Uganda and Zambia). [4] In the Okavango Delta, Botswana, the diet was similar but young crocodiles ate a broader range of insects and invertebrates, with beetles taken in similar numbers to other, similar prey, both aquatic and terrestrial. In Botswana, arachnids were more often found in young crocodiles than in Uganda and Zambia. [89] In Zimbabwe, the dietary composition was broadly similar to that in other areas. [55] However, in the Ugandan portion of Lake Victoria, true bugs and dragonflies both seem to outnumber beetles notably and up to a length of 1 to 2 m (3 ft 3 in to 6 ft 7 in) crocodiles had stomach contents that were made up 70–75% of insects. [90] [91]

    After Nile crocodiles reach 2 m (6 ft 7 in), the significance of most invertebrates in the diet decreases precipitously. [4] [89] An exception to this is in Uganda and Zambia, where subadults and adults of even large sizes, up to 3.84 m (12 ft 7 in), may eat very large numbers of snails. Nearly 70% of the crocodiles examined by Cott (1961) had some remains of snails inside their stomachs. Predation on amuplariid water snails was especially heavy in Bangweulu Swamp, Lake Mweru Wantipa, and the Kafue Flats, where mollusks representing 89.1, 87, and 84.7% of all prey in these locations, respectively. Gastropoda (4126 records per Cott) were taken much more than Lamellibranchiata (six records). Notable favorites include Pila ovata, which lives just under water on rocky surfaces (mainly found in crocodiles from Uganda) and Lanistes ovum, which is found submerged among water plants and on detritus (mainly from stomachs in Zambia). [4]

    Fish Edit

    During the time from when they are roughly 1.5 to 2.2 m (4 ft 11 in to 7 ft 3 in) long (roughly 5 to 9 years old), Nile crocodiles seem to have the broadest diet of any age range. They take more or less much the same small prey as smaller crocodiles, including insects and arachnids, but also take many small to medium-sized vertebrates and quickly become capable taking down prey up to their own weight. Fish become especially significant around this age and size. However, Cott (1961) found that the only size range where fish were numerically dominant over other types of food was from 2 to 3.05 m (6 ft 7 in to 10 ft 0 in). This size range consists of subadult males and a mixture of subadult and adult females. [4] In Lake Turkana, fish were the only food in the stomachs of 45.4% of the crocodiles that did not have empty stomachs, in total 87.8% of the crocodiles that did not have empty stomachs there had fish in their stomachs. Graham (1968) noted that throughout East Africa, crocodile diets are driven by the regional availability of prey. The arid land surrounding Lake Turkana is a relatively barren region for diverse or numerous prey other than fish, so fish are an exceptionally important food source to crocodiles there. [46] [53] In Lake Kyoga and Lake Kwana, 73.1% of the crocodiles that did not have empty stomachs had fish in their stomachs. [92] At Lake St. Lucia in South Africa, many Nile crocodile congregate to feed on striped mullet (Mugil cephalus) as they make their seaward migration for spawning. Here, the crocodiles may line up in dozens across narrow straits of the estuary to effectively force the mullet into easy striking distance, with no observed in-fighting among these crocodile feeding congregations. At this time of plenty (before irrigation operations by humans led St. Lucia to have dangerously high saline levels), a 2.5 m (8 ft 2 in) crocodile could expect to eat 1.1 kg (2.4 lb) of mullet daily, an exceptionally large daily amount for a crocodile. [93]

    Larger fish, like catfish and freshwater bass, are preferred by adults more than 2.2 m (7 ft 3 in) in length. Particularly small fish are likely to be eaten only in case of sudden encounter, mostly in shallow, dry-season ponds where not much effort is needed to catch the small, agile prey. [15] Most observed fishing by crocodiles takes place in waters less than 1.5 m (4 ft 11 in) deep and fish are often caught when they swim into contact with the crocodile's head, even literally right into the reptile's mouth. [46] Across much of their range, they take any fish they encounter, but largish and relatively sluggish mesopredator fish such as lungfish and Barbus carp seem to be most widely reported. Many other genera are taken widely and relatively regularly, including Tilapia (which was the most significant prey genus in Lake Turkana), Clarias, Haplochromis, and Mormyrus. [4] [46] [94] In Uganda and Zambia, lungfish comprised nearly two-thirds of the piscivorian diet for crocodiles. [4] Similarly, in Lake Baringo, the lungfish is the crocodile's main prey and the crocodile is the lungfish's primary predator. [95] In the Okavango Delta, the African pikes (Hepsetus spp.) were the leading prey group for subadults, comprising more than a fourth of the diet. [96] Extremely large fish, such as Nile perch (Lates niloticus), goliath tigerfish (Hydrocynus goliath), and even sharks, are taken on occasion, in addition to big catfish, such as Bagrus spp. and Clarias gariepinus, which are preyed upon quite regularly in areas where they are common. In the Zambezi River and Lake St. Lucia, Nile crocodiles have been known to prey on bull sharks (Carcharhinus leucas) and sand tiger sharks (Carcharias taurus). [97] [98] [99] The largest fishes attacked in such cases may potentially weigh more than 45 kg (99 lb). [100] [101]

    When capturing large fish, they often drag the fish onto shore and swing their heads around to smash the fish onto the ground until it is dead or incapacitated. More modestly sized fish are generally swallowed whole. [46] The Nile crocodile has a reputation as a voracious and destructive feeder on freshwater fish, many of which are essential to the livelihoods of local fisherman and the industry of sport fishing. However, this is very much an unearned reputation. As cold-blooded creatures, Nile crocodiles need to eat far less compared to an equivalent-weighted warm-blooded animal. The crocodile of 2 to 3.05 m (6 ft 7 in to 10 ft 0 in) consumes an average 286 g (10.1 oz) of fish per day. In comparison, piscivorous water birds from Africa eat far more per day despite being a fraction of the body size of a crocodile, for example a cormorant eats up to 1.4 kg (3.1 lb) per day (about 70% of its own body weight), while a pelican consumes up to 3.1 kg (6.8 lb) per day (about 35% of its own weight). [4] [8] The taking of commercially important fish, such as Tilapia, has been mentioned as a source of conflict between humans and crocodiles, and used as justification for crocodile-culling operations however, even a primarily piscivorous crocodile needs relatively so little fish that it cannot deplete fish populations on its own without other (often anthropogenic) influences. [102] Additionally, crocodiles readily take dead or dying fish given the opportunity, thus are likely to incidentally improve the health of some fish species’ populations as this lessens their exposure to diseases and infection. [8]

    Reptiles and amphibians Edit

    Frogs are regionally significant prey for small, young crocodiles in many regions, mainly those in the 0.5 to 1.5 m (1 ft 8 in to 4 ft 11 in) size range. The main amphibian prey species from Uganda and Zambia was the African common toad (Amietophrynus regularis) while in Botswana, the main amphibian prey was the reed frog (Hyperolius viridiflavus). [4] [89] Even the largest frog in the world, the goliath frog (Conraua goliath), has reportedly been preyed on by young Nile crocodiles. [103]

    In general, reptiles become relatively common only in the diet in larger juvenile specimens and subadults. Large reptiles, or armoured reptiles such as turtles, were almost negligible in crocodiles under 2.5 m (8 ft 2 in) and most common in the stomachs of crocodiles over 3.5 m (11 ft 6 in) in length from Uganda and Zambia. Small species of reptiles are largely ignored as prey at this size. Freshwater turtles are often the most frequently recorded reptilian prey, unsurprisingly perhaps because most other reptiles other than a small handful of Lycodonomorphus water snakes are more terrestrial than water-based. [4]

    In a study, the serrated hinged terrapin (Pelusios sinuatus) (also sometimes referred to as the "water tortoise") was more commonly reported in the stomach contents of adult crocodiles from Kruger National Park than any single mammal species. [104] Other turtle species commonly recorded among Nile crocodile prey include the Speke's hinge-back tortoise (Kinixys spekii) and East African black mud turtle (Pelusios subniger). Beyond their ready availability and respectable size, turtles are favored by big crocodiles due to their slowness, which allows the cumbersome crocodiles to capture them more easily than swifter vertebrates. [8] [105] [106] While adults have a sufficient bite force to crush turtle shells, younger crocodiles sometimes are overly ambitious, and will choke to death attempting to swallow whole large river turtles. [19] A variety of snakes has been preyed on from relatively small, innocuous species such as the common egg-eating snake (Dasypeltis scabra) to the largest African snakes species, the African rock python (Python sebae), which can exceed 6.1 m (20 ft 0 in) in length and weigh over 91 kg (201 lb). Venomous species, including the puff adder (Bitis arietans), the forest cobra (Naja melanoleuca), and the black mamba (Dendroaspis polylepis) have been recorded as Nile crocodile prey. [4] [8] The only frequently recorded lizard prey is the large Nile monitor (Varanus niloticus), although this mesopredator may be eaten fairly regularly, as they often share similar habitat preferences, whenever a crocodile is able to ambush the stealthy monitor, which is more agile on land than the bulkier crocodile. [4] [8]

    Birds Edit

    Numerous birds, including storks, small wading birds, waterfowl, eagles, and even small, swift-flying birds, may be snatched. As a whole, birds are quite secondary prey, rarely comprising more than 10–15% of crocodiles' diets, although are taken fairly evenly across all crocodile size ranges, excluding juveniles less than 1 m (3 ft 3 in). [4] [8] [32] Birds most often taken are African darters (Anhinga rufa) and reed (Microcarbo africanus) and white-breasted cormorants (Phalacrocorax lucidus), followed by various waterfowl, including most breeding geese and ducks in Africa. Slow-swimming pelicans are also frequently vulnerable to crocodiles. [107] Nile crocodiles apparently frequently station themselves underneath breeding colonies of darters and cormorants and presumably snatch up fledgling birds as they drop to the water before they can competently escape the saurian, as has been recorded with several other crocodilians. [4] [8]

    Wading birds, even large and relatively slow-moving types such as the goliath heron (Ardea goliath), tend to be highly cautious in avoiding deep water in crocodile-occupied wetlands, whereas cormorants and waterfowl forage over deeper water and are easier for crocodiles to ambush, with Egyptian geese (Alopochen aegyptiaca) and spur-winged geese (Plectropterus gambensis) recorded as being taken largely while flightless due to molting their flight feathers. [108] [109] [110] [111] [112] On the contrary, several records exist of them capturing wading birds. Guggisberg (1972) saw multiple cases of predation on marabou storks (Leptoptilos crumenifer) and around Lake Turkana several may frequent heronries to pick off fledglings. [46] [8] In one case, a crocodile was filmed capturing a striated heron (Butorides striata) in mid-flight. [113] Ospreys (Pandion haliaetus) are known to be grabbed while they dive for fish [114] as are possibly African fish eagles (Haliaeetus vocifer), while crowned eagles (Stephanoaetus coronatus) have reportedly been ambushed on land at carrion. [8] [115] Crocodiles are occasionally successful in grabbing passerines such as weaver birds, including the abundant red-billed quelea (Quelea quelea), and swallows, having been observed to breach the water and in a matter of seconds sweep off a branch full of birds with remarkable success. [8] [116] [117] [118] Larger land birds, such as bustards, guineafowl, ground hornbills (Bucorvus spp.) and ostriches (Struthio camelus), may be taken when they come to water to drink, but like most birds, are seldom harassed and a minor part of the diet. [8] [119]

    Mammals Edit

    Determining the percentage of any specific food item in a crocodile's diet is difficult because their defecation in water makes scat analysis impossible, and capturing individual animals to analyze their stomach contents is painstaking. In addition, as an animal that feeds rarely, sometimes only a few times in a year, even the individual stomach content examinations sometimes prove to be unsuccessful. However, as crocodiles grow, relying solely on small and agile food items such as fish becomes difficult, this causes a shift in the diet as the animal matures, for energy conservation purposes, as in other predators. [4] [46] Nonetheless, starting around 1.5 m (4 ft 11 in), they can become capable mammalian hunters and their ability to overpower a wide range of mammals increases along with their size. Crocodiles less than 3 m (9 ft 10 in) may take a variety of medium–sized mammals up to equal their own mass, including various monkeys, duikers, [120] rodents, hares, pangolins, [4] bats, dik-dik, suni (Neotragus moschatus), [121] oribi (Ourebia ourebi) [122] and other small ungulates up to the size of a Thomson's gazelle (Eudorcas thomsonii). [53]

    Rodents and shrews may enter the diet of juvenile crocodiles, i.e. 1.0 to 1.5 m (3 ft 3 in to 4 ft 11 in), and become commonplace in subadult and small adult crocodiles. Species recorded include the Natal multimammate mouse (Mastomys natalensis), African marsh rat (Dasymys incomtus), common rufous-nosed rat (Oenomys hypoxanthus), and savanna swamp shrew (Crocidura longipes). [4] [89] In many areas, the cane rats are a particular favorite mammalian food for crocodiles, particularly the relatively large greater cane rat (Thryonomys swinderianus). In Uganda and Zambia, the latter species are the leading overall mammalian prey type for crocodiles and one Kenyan crocodile of 2.7 m (8 ft 10 in) in length had 40 greater cane rats in its stomach. [4] [8] [123] Cape porcupines (Hystrix africaeaustralis) are known to have been preyed on several times in Kruger National Park, their quills apparently being an insufficient defense against the tough jaws and digestive systems of crocodiles. [88] [104] Small carnivores are readily taken opportunistically, including both African clawless otters (Aonyx capensis) [124] and spotted-necked otters (Hydrictis maculicollis), [8] as well as water mongoose (Atilax paludinosus), [4] African wildcats (Felis silvestris lybica) [4] and servals (Leptailurus serval). [125]

    Adult Nile crocodiles, i.e. at least 3.05 m (10 ft 0 in), are apex predators. While adults can and will consume nearly all types of prey consumed by the younger specimens, as adult crocodiles gain bulk, they lose much of the necessary maneuverability to capture agile prey such as fish and are not likely to meet their dietary needs by consuming small prey and may expel unnecessary amounts of energy, so take them secondarily to larger prey. [8] [104] Primates of various sizes may be taken by subadult or adult crocodiles. In some areas, some number of baboons is taken, such as in Okavango Delta, where chacma baboons (Papio ursinus) are eaten and Uganda, where olive baboons (Papio anubis) are taken. [126] [127] No records of them hunting apes (other than humans) have been made, but based on a strong reluctance to cross waters with crocodiles and a violent reaction to the visual stimuli of crocodiles, chimpanzees (Pan troglodytes) and gorillas (Gorilla beringei) are thought to consider Nile crocodiles a serious threat. [128] Few details are known about the dietary habits of Nile crocodiles living in Madagascar, although they are considered potential predators of several lemur species. [129] [130] Other nonungulate prey known to be attacked by Nile crocodiles includes aardvarks (Orycteropus afer) [131] and African manatees (Trichechus senegalensis). [132]

    Among the mammals, the bulk of the prey for adults is antelopes. In particular, the genus Kobus is often among the most vulnerable because it forages primarily in wetland areas and seeks to evade more prolific mammalian predators (such as hyenas, lions, etc.) by traveling along waterways. [8] [104] In some cases in Kruger National Park, antelope have been driven into water while being pursued by packs of African wild dogs (Lycaon pictus), which hunt by endurance, engaging prey in a grueling chase until it is exhausted (a very successful hunting style), only to be killed by opportunistic crocodiles. [15] While not as extensively aquatic as the genus Kobus, the reedbucks and the impala (Aepyceros melampus) have both shown a partiality for grasslands adjoining wetlands and riparian zones, so are also very commonly recorded prey items. In Kruger National Park, over the course of 22 years of discontinuous observation, 60% of the large-game kills observed as perpetrated by crocodiles consisted of impala, while more than 15% of observed kills were made up of waterbuck (Kobus ellipsiprymnus), the largest of the genus Kobus at more than 200 kg (440 lb) in weight. [88] [104] Elsewhere, the waterbuck appears to be the most significant mammalian prey for large adult crocodiles, such as in Uganda and Zambia (although due to more sporadic general ungulate populations in those countries, ungulates are less common as prey than in some other countries), as well as in Hluhluwe–iMfolozi Park, South Africa. [4] [133] Other antelopes recorded as prey including gazelles, [88] bushbuck (Tragelaphus scriptus), [104] sitatunga (Tragelaphus spekii), [8] kudu (Tragelaphus strepsiceros), [134] steenbok (Raphicerus campestris), [135] eland (Taurotragus oryx), [88] gemsbok (Oryx gazella), [136] sable (Hippotragus niger) and roan antelopes (Hippotragus equinus), [136] up to a half dozen types of duiker, [121] topi (Damaliscus lunatus), [137] hartebeest (Alcelaphus buselaphus) [8] and both species of wildebeest (Connochaetes sp.). [138]

    Other ungulates are taken by Nile crocodile more or less opportunistically. These may include Grévy's (Equus grevyi) [139] and plains zebras (Equus quagga), [140] pygmy hippopotamus (Choeropsis liberiensis), [141] warthogs (Phacochoerus africanus), [8] bushpigs (Potamochoerus larvatus) [104] and red river hogs (Potamochoerus porcus). [4] In Maasai Mara, Tanzania, large crocodiles congregate at river crossings used by migrating herds of Burchell's zebras and blue wildebeests (Connochaetes taurinus), picking off hundreds of these large ungulates annually. [142] All domesticated ungulates and pet animals will on occasion be hunted by Nile crocodiles, up to the size of dromedary camels (Camelus dromedarius) [143] and cattle (Bos taurus) [144] In Tanzania, up to 54 head of cattle may be lost to crocodiles annually, increasing the human-crocodile conflict level. Goats (Capra aegagrus hircus), donkeys (Equus africanus asinus) and dogs (Canis lupus familiaris) may also rank among the most regularly recorded domesticated animals to be taken by Nile crocodiles. [8] [145]

    Particularly large adults, on occasion, take on even larger prey, such as giraffe (Giraffa camelopardalis), [104] [146] Cape buffalo (Syncerus caffer), [104] [146] and young African bush elephants (Loxodonta africana). [147] [148] Even heavier prey, such as black rhinoceros (Diceros bicornis), have been killed by crocodiles. In one case in the Tana River of Kenya, as observed by Max Fleishmann (communicated via letter to Theodore Roosevelt), a crocodile was able to bring down one of these huge herbivores by the help of muddy bank terrain, the adult female rhino's poor decision to enter deeper water rather than retreat to land and finally having been joined in drowning the animal by one to two other crocodiles. [8] [149] An additional case of predation on an adult black rhino was reportedly observed in northern Zambia. [8] A bull giraffe that lost his footing on a river bank in Kruger National Park was seen to be killed by a large crocodile, while in another case there, a healthy bull buffalo was seen to be overpowered and killed by an average-sized adult male crocodile measuring 4.25 m (13 ft 11 in) after a massive struggle, an incident less commonly seen at this size. [46] [104] Since crocodiles are solitary hunters, the Nile crocodile is the only predator in Africa known to attack full-grown buffaloes alone, compared to the preferred pride attack method of lions. [150]

    Although crocodiles occasionally prey on hippopotamus calves, even large adult crocodiles rarely attack them because of the aggressive defense by mother hippos and the close protection of the herd, which pose a serious threat. Hippopotamus calves have been observed to at times act brazenly around crocodiles, foraging without apparent concern and even bumping into the reptiles. [8] However, some large crocodiles have been recorded as predators of subadult hippos anecdotally, the infamous giant crocodile Gustave was reported to have been seen killing adult female hippos. [88] [104] [151] A 5 m (16 ft 5 in) specimen from Zambia was found to have eaten a "half-grown hippo". [4] At the no-longer-existent Ripon Falls in Uganda, one adult male hippopotamus was seen to be badly injured in a mating battle with a rival bull hippo, and was then subsequently attacked by several crocodiles, causing it to retreat to a reedbed. When the male hippo returned to the water, it was drowned and killed by the group of crocodiles amid "a truly terrifying commotion". [8] However, other than rare instances, adults of megafauna species such as hippopotamuses, rhinoceroses, and elephants are not regular prey and are not typically attacked, with the exception of giraffes, since their anatomy makes them vulnerable to attack while taking a drink.

    Nile crocodiles on occasion prey on big cats including lions and leopards. [104] [120] [138] [152] However, in order to save energy, crocodiles do not prefer such agile animals, as most attacks will end before they can strike. Thus they usually attack agile prey in the absence of regular prey items. [4] [8] Other large carnivores that dwell in Africa near the top of the food chain can also on occasion fall prey to crocodiles. Such predators that can find themselves victim to crocodiles include hyenas (3 out of 4 species reported as prey for Nile crocodiles, only the desert-dwelling brown (Hyaena brunnea) being excluded), [120] [153] African wild dogs, jackals, [88] [104] and cheetahs (Acinonyx jubatus). [53]

    Vegetation Edit

    In the Nile crocodile as well as in at least 13 other species of crocodilian, a variety of fruit (mostly fleshy) has been found in stomach content. While these are probably sometimes used as gastroliths, they are likely often ingested for their nutritional value. Based on these findings, it has also been suggested that crocodiles may act as seed dispersers. [154]

    Interspecific predatory relationships Edit

    Living in the rich biosphere of Africa south of the Sahara, the Nile crocodile may come into contact with multiple other large predators. Its place in the ecosystems it inhabits is largely unique, as it is the only large tetrapod carnivore that spends the majority of its life in water and hunting prey associated with aquatic zones. Large mammalian predators in Africa are often social animals and obligated to feed almost exclusively on terrestrial zones. [15] [104] The Nile crocodile is a strong example of an apex predator. Outside water, crocodiles can meet competition from other dominant savannah predators, notably big cats, which in Africa are represented by lions, cheetahs, and leopards. In general, big cats and crocodiles have a relationship of mutual avoidance. Occasionally, if regular food becomes scarce, both lions and the crocodile will steal kills on land from each other and, depending on size, will be dominant over one another. Both species may be attracted to carrion, and may occasionally fight over both kills or carrion. [155] Most conflicts over food occur near the water and can literally lead to a tug-of-war over a carcass that can end either way, although seldom is there any serious fighting or bloodshed between the large carnivores. [4] Intimidation displays may also resolve these conflicts. However, when size differences are prominent, the predators may prey on each other. 2 cases of Leopards preying on Crocodiles were reported. [156]

    On average, sexual maturity is obtained from 12 to 16 years of age. [47] For males, the onset of sexual maturity occurs when they are about 3.3 m (10 ft 10 in) long and mass of 155 kg (342 lb), being fairly consistent. [157] On the other hand, that for females is rather more variable, and may be indicative of the health of a regional population based on size at sexual maturity. On average, according to Cott (1961), female sexual maturity occurs when they reach 2.2 to 3 m (7 ft 3 in to 9 ft 10 in) in length. [4] Similarly, a wide range of studies from southern Africa found that the average length for females at the onset of sexual maturity was 2.33 m (7 ft 8 in). [158] However, stunted sexual maturity appears to occur in populations at opposite extremes, both where crocodiles are thought to be overpopulated and where they are overly reduced to heavy hunting, sometimes with females laying eggs when they measure as small as 1.5 m (4 ft 11 in) although it is questionable whether such clutches would bear healthy hatchlings. [53] [159]

    According to Bourquin (2008), the average breeding female in southern Africa is between 3 and 3.6 m (9 ft 10 in and 11 ft 10 in). [158] Earlier studies support that breeding is often inconsistent in females less than 3 m (9 ft 10 in) and clutch size is smaller, a female at 2.75 m (9 ft 0 in) reportedly never lays more than 35 eggs, while a female measuring 3.64 m (11 ft 11 in) can expect a clutch of up to 95 eggs. [4] [8] In "stunted" newly mature females from Lake Turkana measuring 1.83 m (6 ft 0 in), the average clutch size was only 15. [46] [53] Graham and Beard (1968) hypothesized that, while females do continue to grow as do males throughout life, that past a certain age and size that females much over 3.2 m (10 ft 6 in) in length in Lake Turkana no longer breed (supported by the physiology of the females examined here) however, subsequent studies in Botswana and South Africa have found evidence of nesting females at least 4.1 m (13 ft 5 in) in length. [53] [158] [160] In the Olifants River in South Africa, rainfall influenced the size of nesting females as only larger females (greater than 3 m (9 ft 10 in)) nested during the driest years. Breeding females along the Olifants were overall larger than those in Zimbabwe. [160] Most females nest only every two to three years while mature males may breed every year. [11] [158]

    During the mating season, males attract females by bellowing, slapping their snouts in the water, blowing water out of their noses, and making a variety of other noises. Among the larger males of a population, territorial clashes can lead to physical fighting between males especially if they are near the same size. Such clashes can be brutal affairs and can end in mortality but typically end with victor and loser still alive, the latter withdrawing into deep waters. [161] [162] Once a female has been attracted, the pair warble and rub the undersides of their jaws together. Compared to the tender behaviour of the female accepting the male, copulation is rather rough (even described as "rape"-like by Graham & Beard (1968)) in which the male often roars and pins the female underwater. [53] [162] Cott noted little detectable discrepancy in the mating habits of Nile crocodiles and American alligators. [4] In some regions, males have reportedly mated with several females, perhaps any female that enters his claimed territory, though in most regions annual monogamy appears to be most common in this species. [19]

    Females lay their eggs about one to two months after mating. The nesting season can fall in nearly every month of the year. In the northern extremes of the distribution (i.e. Somalia or Egypt), the nesting season is December through February while in the southern limits (i.e. South Africa or Tanzania) is in August through December. In crocodiles between these distributions egg-laying is in intermediate months, often focused between April and July. The dates correspond to about a month or two into the dry season within that given region. The benefits of this are presumably that nest flooding risk is considerably reduced at this time and the stage at which hatchlings begin their lives out of the egg falls roughly at the beginning of the rainy season, when water levels are still relatively low but insect prey is in recovery. Preferred nesting locations are sandy shores, dry stream beds, or riverbanks. The female digs a hole a few metres from the bank and up to 0.5 m (20 in) deep, and lays on average between 25 and 80 eggs. The number of eggs varies and depends partially on the size of the female. [53] The most significant prerequisites to a nesting site are soil with the depth to permit the female to dig out the nest mound, shading to which mother can retire during the heat of the day and access to water. [4] She finds a spot soft enough to allow her to dig a sideways slanted burrow. The mother Nile crocodile deposits the eggs in the terminal chamber and packs the sand or earth back over the nest pit. While, like all crocodilians, the Nile crocodile digs out a hole for a nest site, unlike most other modern crocodilians, female Nile crocodiles bury their eggs in sand or soil rather than incubate them in rotting vegetation. [8] [163] The female may micturate sporadically on the soil to keep it moist, which prevents soil from hardening excessively. [8] After burying the eggs, the female then guards them for the three-month incubation period. Nests have been recorded seldom in concealed positions such as under a bush or in grasses, but normally in open spots on the bank. It is thought the Nile crocodile cannot nest under heavy forest cover as can two of the three other African crocodiles because they do not use rotting leaves (a very effective method of producing heat for the eggs) and thus require sunlight on sand or soil the surface of the egg chamber to provide the appropriate warmth for embryo development. In South Africa, the invasive plant Chromolaena odorata has recently exploded along banks traditionally used by crocodiles as nesting sites and caused nest failures by blocking sunlight over the nest chamber. [164]

    When Nile crocodiles have been entirely free from disturbance in the past, they may nest gregariously with the nest lying so close together that after hatching time the rims of craters are almost contiguous. These communal nesting sites are not known to exist today, perhaps being most recently recorded at Ntoroko peninsula, Uganda where two such sites remaining until 1952. In one area, 17 craters were found in an area of 25 yd × 22 yd (75 ft × 66 ft), in another 24 in an area of 26 yd × 24 yd (78 ft × 72 ft). Communal nesting areas also reported from Lake Victoria (up until the 1930s) and also in the 20th century at Rahad River, Lake Turkana and Malawi. [4] [165] [166] [167] The behaviour of the female Nile crocodile is considered unpredictable and may be driven by the regional extent of prior human disturbance and human persecution rather than natural variability. In some areas, the mother crocodiles will only leave the nest if she needs to cool off (thermoregulation) by taking a quick dip or seeking out a patch of shade. [8] Females will not leave nest site even if rocks throw at her back and several authors note her trance-like state while standing near nest, similar to crocodiles in aestivation but not like any other stage in their life-cycle. In such a trance, some mother Nile crocodiles may show no discernable reaction even if pelted with stones. [4] [8] At other times, the female will fiercely attack anything approaching their eggs, sometimes joined by another crocodile which may be the sire of the young. [8] [168] In other areas, the nesting female may disappear upon potential disturbance which may allow the presence of both the female and her buried nest to escape unwanted detection by predators. [11] [53] Despite the attentive care of both parents, the nests are often raided by humans and monitor lizards or other animals while she is temporarily absent. [169]

    At a reported incubation period of about 90 days, the stage is notably shorter than that of the American alligator (110–120 days) but slightly longer than that of the mugger crocodile. [4] [161] Nile crocodiles have temperature-dependent sex determination (TSD), which means the sex of their hatchlings is determined not by genetics as is the case in mammals and birds, but by the average temperature during the middle third of their incubation period. If the temperature inside the nest is below 31.7 °C (89.1 °F), or above 34.5 °C (94.1 °F), the offspring will be female. Males can only be born if the temperature is within that narrow range. [170] The hatchlings start to make a high-pitched chirping noise before hatching, which is the signal for the mother to rip open the nest. [171] [172] It is thought to be either difficult or impossible for hatchlings to escape the nest burrow without assistance, as the surface may become very heavy and packed above them. [4] [53] The mother crocodile may pick up the eggs in her mouth, and roll them between their tongue and the upper palate to help crack the shell and release her offspring. Once the eggs hatch, the female may lead the hatchlings to water, or even carry them there in her mouth, as female American alligators have been observed doing. [4] [8]

    Hatchling Nile crocodiles are between 280 and 300 mm (11 and 12 in) long at first and weigh around 70 g (2.5 oz). The hatchlings grow approximately that length each year for the first several years. [173] The new mother will protect her offspring for up to two years, and if there are multiple nests in the same area, the mothers may form a crèche. During this time, the mothers may pick up their offspring either in their mouths or gular fold (throat pouch), to keep the babies safe. The mother will sometimes carry her young on her back to avoid the natural predators of the small crocodiles, which can be surprisingly bold even with the mother around. Nile crocodiles of under two years are much more rarely observed than larger specimens, and more seldom seen than the same age young in several other types of crocodilian. Young crocodiles are rather shy and evasive due to the formidable gaunlet of predators that they must face in sub-Saharan Africa, spending little time sunning and moving about nocturnally whenever possible. The two-year-and-younger crocodiles may spend a surprising amount of time on land, as evidenced by the range of terrestrial insects found in their stomachs, and their lifestyle may resemble a semi-aquatic mid-sized lizard more so than the very aquatic lives of older crocodiles. [8] [158] At the end of the two years, the hatchlings will be about 1.2 m (3 ft 11 in) long, and will naturally depart the nest area, avoiding the territories of older and larger crocodiles. [8] [158] After this stage, crocodiles may loosely associate with similarly sized crocodiles and many assuredly enter feeding congregations of crocodiles once they attain 2 m (6 ft 7 in), at which size predators and cannibal crocodiles become much less of a concern. [8] Crocodile longevity is not well established, but larger species like the Nile crocodile live longer, and may have a potential average life span of 70 to 100 years, though no crocodilian species commonly exceeds a lifespan of 50 to 60 years in captivity. [7]

    Natural mortality of young Nile crocodiles Edit

    An estimated 10% of eggs will survive to hatch and a mere 1% of young that hatch will successfully reach adulthood. [4] [53] The full range of causes for mortality of young Nile crocodiles is not well understood, as very young and small Nile crocodiles or well-concealed nests are only sporadically observed. Unseasonable flooding (during nesting which corresponds with the regional dry season) is not uncommon and has probably destroyed several nests, although statistical likelihood of such an event is not known. [8] [53] The only aspect of mortality in this age range that is well studied is predation and this is most likely the primary cause of death while the saurians are still diminutive. [174] The single most virulent predator of nests is almost certainly the Nile monitor. This predator can destroy about 50% of studied Nile crocodile eggs on its own, often being successful (as are other nest predators) in light of the trance-like state that the mother crocodile enters while brooding or taking advantage of moments where she is distracted or needs to leave the nest. In comparison, perenties (Varanus giganteus) (the Australian ecological equivalent of the Nile monitor) succeeds in depredating about 90% of freshwater crocodile (Crocodylus johnsoni) eggs and about 25% of saltwater crocodile nests. [174] Mammalian predators can take nearly as heavy of a toll, especially large mongooses such the Egyptian mongoose (Herpestes ichneumon) in the north and the water mongoose in the south of crocodile's range. Opportunistic mammals who attack Nile crocodile nests have included wild pigs, medium-sized wild cats and baboon troops. Like Nile monitors, mammalian predators probably locate crocodile nests by scent as the padded-down mound is easy to miss visually. [15] [174] Marabou storks sometimes follow monitors to pirate crocodile eggs for themselves to consume, although can also dig out nests on their own with their massive, awl-like bills if they can visually discern the nest mound. [8] [174]

    Predators of Nile crocodiles eggs have ranged from insects such as the red flour beetle (Tribolium castaneum) to predators as large and formidable as spotted hyenas (Crocuta crocuta). [174] Unsurprisingly, once exposed to the elements as hatchlings, the young, small Nile crocodiles are even more vulnerable. Most of the predators of eggs also opportunistically eat young crocodiles, including monitors and marabous, plus almost all co-existing raptorial birds, including vultures, eagles, and large owls and buzzards. Many "large waders" are virulent predators of crocodile hatchlings, from dainty little egrets (Egretta garzetta) and compact hamerkops (Scopus umbretta) to towering saddle-billed storks (Ephippiorhynchus senegalensis), goliath herons and shoebills (Balaeniceps rex). Larger corvids and some non-wading water birds (i.e. pelicans) can also take some young Nile crocodiles. Mammalian carnivores take many hatchlings as well as large turtles and snakes, large predatory freshwater fish, such as the African tigerfish, the introduced largemouth bass, and possibly bull sharks, when they enter river systems. When crocodile nests are dug out and the young placed in water by the mother, in areas such as Royal Natal National Park predators can essentially enter a feeding frenzy. [174] [175] [176] [177] It may take a few years before predation is no longer a major cause of mortality for young crocodiles. African fish eagles can take crocodile hatchlings up to a few months of age and honey badgers can prey on yearlings. Once they reach their juvenile stage, very large African rock pythons and big cats remain as the only predatory threat to young crocodiles. [7] [8] [178] Perhaps no predator is more deadly to young Nile crocodiles than larger crocodiles of their own species, as, like most crocodilians, they are cannibalistic. This species may be particularly dangerous to their own kind considering the aggressive disposition they tend to bear. [8] [80] [179] While the mother crocodile will react aggressively toward potential predators and has been recorded chasing and occasionally catching and killing such interlopers into her range, due to the sheer number of animals who feed on baby crocodiles and the large number of hatchlings, she is more often unsuccessful at deflecting such predators. [4] [8] [174]

    Conservation organizations have determined that the main threats to Nile crocodiles, in turn, are loss of habitat, pollution, hunting, and human activities such as accidental entanglement in fishing nets. [22] Though the Nile crocodile has been hunted since ancient times, [180] the advent of the readily available firearm made it much easier to kill these potentially dangerous reptiles. [8] The species began to be hunted on a much larger scale from the 1940s to the 1960s, primarily for high-quality leather, although also for meat with its purported curative properties. The population was severely depleted, and the species faced extinction. National laws, and international trade regulations have resulted in a resurgence in many areas, and the species as a whole is no longer wholly threatened with extinction. The status of Nile crocodiles was variable based on the regional prosperity and extent of conserved wetlands by the 1970s. [181] However, as is the case for many large animal species whether they are protected or not, persecution and poaching have continued apace and between the 1950s and 1980s, an estimated 3 million Nile crocodiles were slaughtered by humans for the leather trade. [19] In Lake Sibaya, South Africa, it was determined that in the 21st century, persecution continues as the direct cause for the inability of Nile crocodiles to recover after the leather trade last century. [182] Recovery for the species appears quite gradual and few areas have recovered to bear crocodile populations, i.e. largely insufficient to produce sustainable populations of young crocodiles, on par with times prior to the peak of leather trading. [159] Crocodile 'protection programs' are artificial environments where crocodiles exist safely and without the threat of extermination from hunters. [58]

    An estimated 250,000 to 500,000 individuals occur in the wild today. The IUCN Red List assesses the Nile crocodile as "Least Concern (LR/lc)". [1] The CITES lists the Nile crocodile under Appendix I (threatened with extinction) in most of its range and under Appendix II (not threatened, but trade must be controlled) in the remainder, which either allows ranching or sets an annual quota of skins taken from the wild. The Nile crocodile is also widely distributed, with strong, documented populations in many countries in eastern and southern Africa, including Somalia, Ethiopia, Kenya, Zambia and Zimbabwe. [1] [22] This species is farmed for its meat and leather in some parts of Africa. Successful sustainable-yield programs focused on ranching crocodiles for their skins have been successfully implemented in this area, and even countries with quotas are moving toward ranching. In 1993, 80,000 Nile crocodile skins were produced, the majority from ranches in Zimbabwe and South Africa. [159] [183] Crocodile farming is one of the few burgeoning industries in Zimbabwe. [184] Unlike American alligator flesh, Nile crocodile meat is generally considered unappetizing although edible as tribes such as the Turkana may opportunistically feed on them. According to Graham and Beard (1968), Nile crocodile meat has an "indescribable" and unpleasant taste, greasy texture and a "repellent" smell. [53] [185]

    The conservation situation is more grim in central and west Africa presumably for both the Nile and west African crocodiles. The crocodile population in this area is much more sparse, and has not been adequately surveyed. While the natural population in these areas may be lower due to a less-than-ideal environment and competition with sympatric slender-snouted and dwarf crocodiles, extirpation may be a serious threat in some of these areas. [22] [186] At some point in the 20th century, the Nile crocodile appeared to have been extirpated as a breeding species from Egypt, but has locally re-established in some areas such as the Aswan Dam. [19] Additional factors are a loss of wetland habitats, which is addition to direct dredging, damming and irrigation by humans, has retracted in the east, south and north of the crocodile's range, possibly in correlation with global warming. [19] [187] Retraction of wetlands due both to direct habitat destruction by humans and environmental factor possibly related to global warming is perhaps linked to the extinction of Nile crocodiles in the last few centuries in Syria, Israel and Tunisia. [19] [22] In Lake St. Lucia, highly saline water has been pumped into the already brackish waters due to irrigation practices. Some deaths of crocodiles appeared to have been caused by these dangerous saline levels and this one-time stronghold for breeding crocodiles has experienced a major population decline. [19] [188] In yet another historic crocodile stronghold, the Olifants River, which flows through Kruger National Park, numerous crocodile deaths have been reported. These are officially due to unknown causes but analysis has indicated that environmental pollutants caused by humans, particularly the burgeoning coal industry, are the primary cause. Much of the contamination of crocodiles occurs when they consume rancid fish themselves killed by pollutants. [189] [190] Additional ecological surveys and establishing management programs are necessary to resolve these questions.

    The Nile crocodile is the top predator in its environment, and is responsible for checking the population of mesopredator species, such as the barbel catfish and lungfish, that could overeat fish populations on which other species, including birds, rely. One of the fish predators seriously affected by the unchecked mesopredator fish populations (due again to crocodile declines) is humans, particularly with respect to tilapia, an important commercial fish that has declined due to excessive predation. [8] The Nile crocodile also consumes dead animals that would otherwise pollute the waters.

    Attacks on humans Edit

    Much of the hunting of and general animosity toward Nile crocodiles stems from their reputation as a man-eater, which is not entirely unjustified. [191] Despite most attacks going unreported, the Nile crocodile along with the saltwater crocodile is estimated to kill hundreds (possibly thousands) of people each year, which is more than all other crocodilian species combined. [7] [16] [192] [193] While these species are much more aggressive toward people than other living crocodilians (as is statistically supported by estimated numbers of crocodile attacks), Nile crocodiles are not particularly more likely to behave aggressively to humans or regard humans as potential prey than saltwater crocodiles. However, unlike other "man-eating" crocodile species, including the saltwater crocodile, the Nile crocodile lives in close proximity to human populations through most of its range, so contact is more frequent. This combined with the species’ large size renders a higher risk of attack. [7] [12] Crocodiles as small as 2.1 m (6 ft 11 in) are capable of overpowering and successfully preying on small apes and hominids, presumably including children and smaller adult humans, but a majority of fatal attacks on humans are by crocodiles reportedly exceeding 3 m (9 ft 10 in) in length. [12]

    In studies preceding the slaughter of crocodiles for the leather trade, when there were believed to be many more Nile crocodiles, a roughly estimated 1,000 human fatalities per annum by Nile crocodiles were posited with a roughly equal number of aborted attacks. [8] [194] A more contemporary study claimed the number of attacks by Nile crocodiles per year as 275 to 745, of which 63% are fatal, as opposed to an estimated 30 attacks per year by saltwater crocodiles, of which 50% are fatal. With the Nile crocodile and the saltwater crocodile, the mean size of crocodiles involved in non-fatal attacks was about 3 m (9 ft 10 in) as opposed to a reported range of 2.5–5 m (8 ft 2 in–16 ft 5 in) or larger for crocodiles responsible for fatal attacks. The average estimated size of Nile crocodiles involved in fatal attacks is 3.5 m (11 ft 6 in). Since a majority of fatal attacks are believed to be predatory in nature, the Nile crocodile can be considered the most prolific predator of humans among wild animals. [195] In comparison, lions, in the years from 1990 to 2006, were responsible for an estimated one-eighth as many fatal attacks on humans in Africa as were Nile crocodiles. Although Nile crocodiles are more than a dozen times more numerous than lions in the wild, probably fewer than a quarter of living Nile crocodiles are old and large enough to pose a danger to humans. [195] [196] [197] Other wild animals responsible for more annual human mortalities either attack humans in self-defense, as do venomous snakes, [198] or are deadly only as vectors of disease or infection, such as snails, [199] rats [200] and mosquitos. [201]

    Regional reportage from numerous areas with large crocodile populations nearby indicate, per district or large village, that crocodiles often annually claim about a dozen or more lives per year. Miscellaneous examples of areas in the last few decades with a dozen or more fatal crocodile attacks annually include Korogwe District, Tanzania, Niassa Reserve, Mozambique and the area around Lower Zambezi National Park, Zambia. [202] [203] Despite historic claims that the victims of Nile crocodile attacks are usually "women and children", [7] there is no detectable trends in this regard and any human, regardless of age, gender, or size is potentially vulnerable. Incautious human behavior is the primary drive behind crocodile attacks. [12] Most fatal attacks occur when a person is standing a few feet away from water on a non-steep bank, is wading in shallow waters, actively swimming or have limbs dangling over a boat or pier. Many victims are caught while crouching and people in jobs that might require heavy usage of water including laundry workers, fisherman, game wardens and regional guides are more likely to be attacked. Many fisherman and other workers who are not poverty-stricken will go out of their way to avoid waterways known to harbor large crocodile populations. [8] [53] [204]

    Most biologists who have engaged in months or even years of field work with Nile crocodiles, including Cott (1961), Graham and Beard (1968) and Guggisberg (1972), have found that with sufficient precautions, their own lives and the lives of their local guides were rarely, if ever, at risk in areas with many crocodiles. [4] [8] [53] However, Guggisberg accumulated several earlier writings that noted the lack of fear of crocodiles among Africans, driven in part perhaps by poverty and superstition, that caused many observed cases of an "appalling" lack of caution within view of large crocodiles, as opposed to the presence of bold lions which engendered an appropriate panic. Per Guggisberg, this disregard (essentially regarding the crocodile as a lowly creature and thus non-threatening to humans) may account for the seemingly higher frequency of deadly attacks by crocodiles than by large mammalian carnivores. Most locals are well aware of how to behave in crocodile-occupied areas and some of the writings quoted by Guggisberg from the 19th and 20th century may require being taken with a "grain of salt". [8] [53]