Why didn't the polar bear change its color from white to black during evolution to absorb heat?

Why didn't the polar bear change its color from white to black during evolution to absorb heat?

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Polar bears are white in color and white color is not a good absorbant of heat. Why then didn't they evolve a black color to absorb more heat?

Polar bears do not have white fur - they don't have pigments in their fur hairs which makes them clear and translucent. The outer fur consists of hollow fibres, which shatter a part of the incoming light (the visible part) which makes them look white. This gives a very good camouflage in a white environment.

It was initially thought (see reference 1) that the hollow fibers work in the same way as fiber optic cables and direct the UV part of the light (the visible was thought to be shattered) towards the black skin of the bears where it generates heat, but this hypothesis has been disproved. The UV part of the light is simply absorbed by the bears outer fur and doesn't reach the skin (see reference 2 for details).

The hollow hair helps with the insulation of the skin and can change the color due to environmental influences. The tend to get yellow after feeding on seals due to the fatty substances from the animals. There have also been reports from zoos that algae lived inside the hollow part of the fur making the animals more grey and sometimes even green (see reference 3).


  1. Light collection and solar sensing through the polar bear pelt
  2. Is polar bear hair fiber optic?
  3. The greening of polar bears in zoos

Bears initially were dark. But in snow it is really poor camouflage, their victims will see them to early. So they evolved to white color.
They have a lot of fat and good fur to keep the temperature, they don't really need more sun energy. They need more food.
In the same way - in the forest all bears are dark - for camouflage.
Read here

How much energy could an Arctic-dwelling creature be expected to capture from sunlight? I think not very much. How much can it gain from having coloration that allows it to capture prey more easily? Quite a bit. Also, given the size of the polar bear, they will probably be generating more than enough waste heat from metabolic activity. Indeed, if you do a little research, you might discover that the polar bear's problem is, indeed, getting rid of heat:

In bears, the basal metabolic rate varies with climate and season; Polar Bear has highest BMR. Overheat easily when running; can't travel any great distance at speeds more than a walk. Low surface-area to volume ratio favors heat retention. Tendency to overheat enhanced by layer of fat 11 cm (4.5in) thick. Young cubs up to 6 months old, with little body fat, are susceptible to cold. Use more than twice the predicted energy for moving at a given speed, perhaps due to bulky body. Fat and fur both insulate. As long as bear isn't exposed to wind, body temperature and metabolic rate remain normal at -37 degrees C (-35 degrees F).


Of course, even if the polar bear was a perfect absorber, it could get at most ~1kW/m^2 of energy from the sun, and that only on a clear day in the summer. And that heat would be on the outside of its insulating fur & fat.

So there's the answer: a strong selective pressure towards white, little or none towards black.

Re waste heat: What is meant here is that when the polar bear (or any animal) consumes food, part of it goes to producing heat as an unavoidable byproduct of metabolism. Larger animals usually have to get rid of excess heat, thanks to the surface/volume relationship mentioned in the comments.

For a reference, try thinking about this: And remember that not all answers are written down in a book (or web site, these days). Sometimes you have to actually think and reason out your own answers :-)

Added: I think the problem with this question is the assumption that polar bears (or indeed, any boreal mammal) need to absorb heat. Maybe that's down to anthropocentrism, since humans evolved from ancestors that lived in tropical climes, and so have adaptations (like sweating & nearly hairless skin) for cooling. But if you read the links, you discover that more often the problem is getting rid of excess metabolic heat, and most boreal mammals seem quite comfortable in what we primates consider cold. (I write this after coming in from playing with my two dogs, who love to run around in the fresh snow.)

You might also think about why almost all (non-domesticated) mammals have evolved protective or camouflaging coloration. (The only exception I can think of offhand is the skunk.) Indeed, a number of boreal mammals have evolved seasonal color changes (e.g. ), having darker summer colors (like their more southerly relatives), but turning white in winter. That suggests that the benefits of camouflage strongly outweigh any possible benefit from solar heat gain.

In addition to camouflage, consider that during the colder parts of the year, when they need the heat the most, the nights are longer than the day.

Darker fur would radiate more heat away from the body than the lighter fur.

So it's possible that they did evolve the white fur for heat - but in their environment, the coldest part of the year heat retention is more critical than heat gathering, and this would bias towards white fur, not black.

Although black is a better absorber of (heat) radiation, it is also a better emitter too. As Polar bears live in a cold environment, having black hair would cause them to radiate their body heat away more quickly. Their colour helps them to retain heat better - dark objects equilibrate to the temperature of their surrounding faster, lighter objects more slowly. If they were darker, they would require more food to survive.

Their black skin is irrelevant as the light has already been scattered/reflected away by the white/colourless hairs - as they look white, it's the reflected light that you are seeing.

Why then didn't they evolve a black color to absorb more heat?

This assumes that evolution is an active process, working by organisms' will or need.

Do not forget that the theory of evolution works from generation to generation, by random (imperfect and chaotic) mutations, most of which are unfavorable.

The polar bears did not evolve a black color because they can't decide that. If you believe in evolution, and you believe that a black color would draw more heat, increasing the animal's chances of survival over its white peers (so much that the white peers would eventually die off), then we are simply waiting for the black color to come around. Evolution is never finished.

This is a brief expansion on DrAlchemist's response; one that I intended to make myself, but saw that s/he had already covered the basics.

To see that black is a better emitter of heat we have to leave biology and go to physics, specifically quantum mechanics, even more specifically black body radiation. Like most things, absorption and radiation are equally balanced when it comes to a given material/color. A white object is slow to absorb heat and a black object is quick to absorb heat, as we have likely all seen demonstrated in elementary school. What my teacher (and likely yours) did not mention is that the white object cools slowly when taken out of the sun, but the black object will cool much more quickly. Black heats up quickly, and radiates just as quickly when the temperature differential inverts.

As a mental exercise, consider an idealized object that absorbs electromagnetic energy perfectly, called a black body. Turn a heat lamp on it, and it will absorb all the heat it receives. Turn the lamp off and, as in the argument above, it will become a perfect emitter of the radiation it absorbed.

I think an important point hasn't been mentioned yet.

Why then didn't they evolve a black color

The changes introduced by evolution initially are random. Only the persistence of those changes over generations can be thought of in a "smart" way.

Technically, evolution can lead to some things getting worse! For example, if mutations improve a creatures eye-sight but at the same time worsen it's hearing, both traits may end up surviving assuming the improved eye-sight makes more of a difference than the worsened hearing.

Well, Polar bears do have black skin; But, living in the harsh arctic conditions they've adapted several traits such as thick layer of blubber, wide paws etc. But their most peculiar trait is having a white fur coat; unlike other bears, polar bears have evolved to have white fur with hollow hairs which easily allows their black skin to absorb the radiations from the sun. So there's no problem with the heat intake.

Now, the reason behind their white fur lies in their quest to food. The white fur enables them to easily hide/blanket in their surrounding (the white masses of snow) i.e. it helps them in camouflage.

And, I guess that's it! Thanks!

The Polar Bear is a large species of bear that is found inhabiting the ice fields in the Arctic Ocean. It is the biggest species of bear in the world (with the exception of the Kodiak Brown Bears found in Alaska which can reach similar sizes) with males often weighing-in at around 600kg. Thought to be closely related to the Brown Bear, the Polar Bears’ name actually means “Sea Bear” as they are known to not just spend a great deal of time close to the coast, but are also strong and capable swimmers that have been spotted up to 100 miles from the closest ice or land. They are however being devastatingly affected by global warming as the ice that they rely so heavily on is disappearing fast and has led to the Polar Bear becoming a strong symbol of the effects of climate change. Polar Bear populations have also fallen across the Arctic Ocean due to hunting, pollution and drilling for oil and gas leading to them being as listed as a threatened species.

Adult Polar Bears are animals that typically measure more than two meters in length and weigh around half a tonne. Females though are much lighter than their male counterparts that are almost double their weight. Polar Bears are one of the few large mammals found in such hostile conditions and have adapted well to their life on the ice. Their fur is thick and dense and is made up of a warm undercoat with longer guard hairs on top that are clear, hollow tubes that trap warmth from the sun and transmit it directly down to their black skin, which then absorbs the welcome heat. The Polar Bear is an animal with a strong and muscular body with broad front paws that help when paddling in the water, and fur on the bottom of its feet that not only helps to keep them warm but also gives the Polar Bear extra grip when moving about on the ice. They have very long necks in comparison to other bear species which enables their head to remain above the water when swimming. They also have more elongated muzzles and smaller ears than their relatives.

More Polar Bears 101 Facts

Arctic weather can be fiercely cold. As humans, we need protective clothing and/or shelter to stay warm. Polar bears don’t. Their bodies thrive in the stark temperatures.

Built For the North

In the High Arctic, the sun sets in October and doesn't rise again until late February. Winter temperatures can plunge to -40° or -46 C (-50 F) and stay that way for days or weeks. The average January and February temperature is -34 C (-29 F).

Bears are insulated with two layers of fur and a thick layer of body fat. This provides enough insulation that their body temperature and metabolic rate doesn’t change, even when temperatures reach -37 C (-34 F).

To learn more about how polar bear’s bodies adjust to their climate, see physical characteristics. A polar bear's body temperature, 37 C (98.6 F), is average for mammals.

On bitterly cold days with fierce winds, polar bears dig shelter pits in snow banks and curl up in a tight ball. Sometimes they cover their muzzles—which radiate heat—with their thickly furred paws and let the snow drift around and over them.

Polar bears have more problems with overheating than they do with cold. That's why they typically walk at a leisurely pace. They can quickly overheat when they run.

Top 7 Adaptations Of A Polar Bear

Massive Size

With a massive body structure, polar bears are larger than their counterparts i.e. grizzly bears. As a result, the heat does not escape from the body of a polar bear and keeps it warm. Scientifically speaking, such animals possess a high ratio of volume to surface area due to which their skin smoke out minimum amount of heat from their body, according to Dr. Andrew Derocher. It’s a usual phenomenon that is readily found in animals living in icy environments and hence one of the usual adaptations of a polar bear.

Polar bear is sleeping | Image courtesy of

Tail And Ears

If an animal has an external part that sticks out from the body of that animal, it may influence the volume to surface area ratio. As a result, the skin of an animal dispels more heat. However in case of polar bear, the polar bear tail and ears are quite small thereby allowing relatively minimum surface area as compare to the bigger ears. Consequently, it enables the animal to conserve heat inside its body.

Layer Of Fat

With a 4-inch dense coating of fat spread out over the body under the polar bear skin , the unpleasantly cold weather cannot make a way into the polar bear. So it’s one of the most important adaptations of a polar bear. Though this layer normally protects a polar bear yet it also keeps them warm and cozy in frozen conditions. As compare to their counterparts, polar bear’s milk contains a lot of useful protein and fat which keeps their cubs safe from cold weather.

Pattern Of Eating

A polar bear is a flesh-eating mammal that gobbles foliage along with other meat like whales and seals. Since red meat contains even more calories as compare to undergrowth so it gives him great calories with every single bite of meal. These animals take high-fat diet that help giving them extra strength in chilly weather. Hence such diet is indispensable for the existence of polar bear and without which they would not last for too long in these frozen temperatures. Hence, one of the useful adaptations of a polar bear. A mother polar bear oozes high-fat milk from her mammary glands that contains 31% fat in it. So when cubs slurp this milk, it gives them extra strength by maintaining the temperature inside their body and also helps in their growth.

Thick Fleece

The body of a polar bear is insulated with a dense fur that extends out to the whole body apart for its nose. Unlike other bears, polar bears possess even more compact and thick fleece. The fleece along with thick hair keeps them warm even while passing through chilly waters. Besides, this fleece also tends to mirror light and appearing even whiter thereby disguising him perfectly under the snow. Every year, polar bear changes the shade of their fleece as it appears snowy in winter and creamy shade in fall. In chilly conditions of winter, the fleece of polar bear works like a stove as it takes hot air direct from sunlight and keeps him warm. Also since the crust below this covering is dark so it also helps in absorbing heat from sunlight. This polar bear skin color is one of the fine adaptations of a polar bear as he hides himself in the snow while stalking.

Water Proof Hair

The hair of polar bear is just like a jacket which releases water as the animal finishes off swimming. In this way, such animals are able to keep themselves warm and their body does not become wet for too long. As polar bear pops up from water, he tends to turn over his body on the snow and their fur manages to get dry as a bone by means of oil which is present inside their fur. The underlying principle is that as long as water stays, it will try to absorb the heat of a body and so animal will start feeling cold. That’s why as polar bears rise from water, they try to dry out themselves as quickly as possible. Therefore hair works as one of the wonderful adaptations of a polar bear.

Big Anti-Slip Paws

If you ever happen to witness the paws of a polar bear, you will come to realize that their paws are huge. These paws work like snowshoes on heavy snow, balance the weight of the animal thereby enabling polar bears to navigate easily even on wafer-thin ice layer. Thus, one of the great adaptations of a polar bear is it’s paws. These paws are extremely helpful while strolling because they have special footpads insulated by little smooth lumps known as papillae. Besides polar bears also have dense and curled claws that allow them to walk easily without getting slip or slide into the snow. These features enable them to sprint even on heavy snow and also allow him to halt at any moment. Finally, there is a dense fleece over these paws that not only keep them warm under shivering cold but also provide enough adhesive friction while sprinting on gleaming surface.

Read More about Polar Bears:

  • Do Polar Bears Hibernate
  • Are Polar Bears Endangered?
  • Why Are Polar Bears Endangered
  • Information About Polar Bears
  • Polar Bear Facts For Kids

Polar Bear is an amazing animal living against the extremes of the weather. What do you think about the adaptations of a polar bear? Share your thoughts in the comments below.

Some not-amazing polar bear facts

Polar bears were one of the first species to become threatened due to anthropogenic climate change. They rely on sea ice to cover large areas in search of food. A longer melting season due to climate change means that sea ice is forming later and breaking up earlier in the year, restricting the polar bears’ feeding range. This is particularly impactful on pregnant females, who need to build up fat stores to live off of when birthing and nursing cubs.

Other risks include pollution in the form of toxic contaminants, conflicts with shipping, oil and gas exploration and development, hunting, and human-bear interactions including harvesting and possible stresses from recreational polar-bear watching.

Organizations such as WWF are working hard to secure a future for polar bears. You can help them by adopting a polar bear and supporting their crucial on-the-ground research and conservation projects. You can also check out the polar bear tracker to see the polar bears they are monitoring and what they learn from them.


Constantine John Phipps was the first to describe the polar bear as a distinct species in 1774 in his report about his 1773 expedition towards the North Pole. [3] [2] He chose the scientific name Ursus maritimus, the Latin for 'maritime bear', [14] due to the animal's native habitat. The Inuit refer to the animal as nanook (transliterated as nanuq in the Inupiat language). [15] [13] The Yupik also refer to the bear as nanuuk in Siberian Yupik. [16] The bear is umka in the Chukchi language. In Russian, it is usually called бе́лый медве́дь (bélyj medvédj, the white bear), though an older word still in use is ошку́й (Oshkúj, which comes from the Komi oski, "bear"). [17] In Quebec, the polar bear is referred to as ours blanc ("white bear") or ours polaire ("polar bear"). [18] In the Norwegian-administered Svalbard archipelago, the polar bear is referred to as Isbjørn ("ice bear").

The polar bear was previously considered to be in its own genus, Thalarctos. [19] However, evidence of hybrids between polar bears and brown bears, and of the recent evolutionary divergence of the two species, does not support the establishment of this separate genus, and the accepted scientific name is now therefore Ursus maritimus, as Phipps originally proposed. [2]

The bear family, Ursidae, is thought to have split from other carnivorans about 38 million years ago. [20] The subfamily Ursinae originated approximately 4.2 million years ago. [21] The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004. [22] Fossils show that between 10,000 and 20,000 years ago, the polar bear's molar teeth changed significantly from those of the brown bear. [23] Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene [4] from the eastern part of Siberia (from Kamchatka and the Kolym Peninsula). [23]

The evidence from DNA analysis is more complex. The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear, Ursus arctos, roughly 150,000 years ago. [22] Further, some clades of brown bear, as assessed by their mtDNA, were thought to be more closely related to polar bears than to other brown bears, [24] meaning that the brown bear might not be considered a species under some species concepts, but paraphyletic. [25] The mtDNA of extinct Irish brown bears is particularly close to polar bears. [26] A comparison of the nuclear genome of polar bears with that of brown bears revealed a different pattern, the two forming genetically distinct clades that diverged approximately 603,000 years ago, [27] although the latest research is based on analysis of the complete genomes (rather than just the mitochondria or partial nuclear genomes) of polar and brown bears, and establishes the divergence of polar and brown bears at 400,000 years ago. [28]

However, the two species have mated intermittently for all that time, most likely coming into contact with each other during warming periods, when polar bears were driven onto land and brown bears migrated northward. Most brown bears have about 2 percent genetic material from polar bears, but one population, the ABC Islands bears, has between 5 percent and 10 percent polar bear genes, indicating more frequent and recent mating. [29] Polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids [4] [30] rather than indicating that they have only recently diverged, the new evidence suggests more frequent mating has continued over a longer period of time, and thus the two bears remain genetically similar. [29] However, because neither species can survive long in the other's ecological niche, and because they have different morphology, metabolism, social and feeding behaviours, and other phenotypic characteristics, the two bears are generally classified as separate species. [31]

When the polar bear was originally documented, two subspecies were identified: the American polar bear (Ursus maritimus maritimus) by Constantine J. Phipps in 1774, and the Siberian polar bear (Ursus maritimus marinus) by Peter Simon Pallas in 1776. [32] This distinction has since been invalidated. [33] [34] [35] One alleged fossil subspecies has been identified: Ursus maritimus tyrannus, which became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies. [4] However, recent reanalysis of the fossil suggests that it was actually a brown bear. [1]

The polar bear is found in the Arctic Circle and adjacent land masses as far south as Newfoundland. Due to the absence of human development in its remote habitat, it retains more of its original range than any other extant carnivore. [36] While they are rare north of 88°, there is evidence that they range all the way across the Arctic, and as far south as James Bay in Canada. Their southernmost range is near the boundary between the subarctic and humid continental climate zones. They can occasionally drift widely with the sea ice, and there have been anecdotal sightings as far south as Berlevåg on the Norwegian mainland and the Kuril Islands in the Sea of Okhotsk. It is difficult to estimate a global population of polar bears as much of the range has been poorly studied however, biologists use a working estimate of about 20–25,000 or 22–31,000 polar bears worldwide. [2] [37] [38]

There are 19 generally recognized, discrete subpopulations, though polar bears are thought to exist only in low densities in the area of the Arctic Basin. [37] [39] The subpopulations display seasonal fidelity to particular areas, but DNA studies show that they are not reproductively isolated. [35] The 13 North American subpopulations range from the Beaufort Sea south to Hudson Bay and east to Baffin Bay in western Greenland and account for about 54% of the global population. [40]

The range includes the territory of five nations: Denmark (Greenland), Norway (Svalbard), Russia, the United States (Alaska) and Canada. These five nations are the signatories of the International Agreement on the Conservation of Polar Bears, which mandates cooperation on research and conservation efforts throughout the polar bear's range. [41] Bears sometimes swim to Iceland from Greenland—about 600 sightings since the country's settlement in the 9th century AD, and five in the 21st century as of 2016 [update] —and are always killed because of their danger, and the cost and difficulty of repatriation. [42]

Modern methods of tracking polar bear populations have been implemented only since the mid-1980s, and are expensive to perform consistently over a large area. The most accurate counts require flying a helicopter in the Arctic climate to find polar bears, shooting a tranquilizer dart at the bear to sedate it, and then tagging the bear. In Nunavut, some Inuit have reported increases in bear sightings around human settlements in recent years, leading to a belief that populations are increasing. Scientists have responded by noting that hungry bears may be congregating around human settlements, leading to the illusion that populations are higher than they actually are. [43] The Polar Bear Specialist Group of the IUCN Species Survival Commission takes the position that "estimates of subpopulation size or sustainable harvest levels should not be made solely on the basis of traditional ecological knowledge without supporting scientific studies." [44]

Of the 19 recognized polar bear subpopulations, one is in decline, two are increasing, seven are stable, and nine have insufficient data, as of 2017. [45]

The polar bear is a marine mammal because it spends many months of the year at sea. [46] However, it is the only living marine mammal with powerful, large limbs and feet that allow them to cover kilometres on foot and run on land. [47] Its preferred habitat is the annual sea ice covering the waters over the continental shelf and the Arctic inter-island archipelagos. These areas, known as the "Arctic ring of life", have high biological productivity in comparison to the deep waters of the high Arctic. [36] [48] The polar bear tends to frequent areas where sea ice meets water, such as polynyas and leads (temporary stretches of open water in Arctic ice), to hunt the seals that make up most of its diet. [49] Freshwater is limited in these environments because it is either locked up in snow or saline. Polar bears are able to produce water through the metabolism of fats found in seal blubber, [50] and are therefore found primarily along the perimeter of the polar ice pack, rather than in the Polar Basin close to the North Pole where the density of seals is low. [51]

Annual ice contains areas of water that appear and disappear throughout the year as the weather changes. Seals migrate in response to these changes, and polar bears must follow their prey. In Hudson Bay, James Bay, and some other areas, the ice melts completely each summer (an event often referred to as "ice-floe breakup"), forcing polar bears to go onto land and wait through the months until the next freeze-up. [48] In the Chukchi and Beaufort seas, polar bears retreat each summer to the ice further north that remains frozen year-round.

The only other bear similar in size to the polar bear is the Kodiak bear, which is a subspecies of brown bear. [52] Adult male polar bears weigh 350–700 kg (770–1,500 lb) and measure 2.4–3 metres (7 ft 10 in–9 ft 10 in) in total length. [53] Around the Beaufort Sea, however, mature males reportedly average 450 kg (1,000 lb). [54] Adult females are roughly half the size of males and normally weigh 150–250 kg (330–550 lb), measuring 1.8–2.4 metres (5 ft 11 in–7 ft 10 in) in length. Elsewhere, a slightly larger estimated average weight of 260 kg (570 lb) was claimed for adult females. [55] When pregnant, however, females can weigh as much as 500 kg (1,100 lb). [53] The polar bear is among the most sexually dimorphic of mammals, surpassed only by the pinnipeds such as elephant seals. [56] The largest polar bear on record, reportedly weighing 1,002 kg (2,209 lb), was a male shot at Kotzebue Sound in northwestern Alaska in 1960. This specimen, when mounted, stood 3.39 m (11 ft 1 in) tall on its hindlegs. The shoulder height of an adult polar bear is 122 to 160 cm (4 ft 0 in to 5 ft 3 in). [57] [58] While all bears are short-tailed, the polar bear's tail is relatively the shortest amongst living bears, ranging from 7 to 13 cm (2.8 to 5.1 in) in length. [59]

Compared with its closest relative, the brown bear, the polar bear has a more elongated body build and a longer skull and nose. [31] As predicted by Allen's rule for a northerly animal, the legs are stocky and the ears and tail are small. [31] However, the feet are very large to distribute load when walking on snow or thin ice and to provide propulsion when swimming they may measure 30 cm (12 in) across in an adult. [60] The pads of the paws are covered with small, soft papillae (dermal bumps), which provide traction on the ice. The polar bear's claws are short and stocky compared to those of the brown bear, perhaps to serve the former's need to grip heavy prey and ice. [31] The claws are deeply scooped on the underside to assist in digging in the ice of the natural habitat. Research of injury patterns in polar bear forelimbs found injuries to the right forelimb to be more frequent than those to the left, suggesting, perhaps, right-handedness. [61] Unlike the brown bear, polar bears in captivity are rarely overweight or particularly large, possibly as a reaction to the warm conditions of most zoos.

The 42 teeth of a polar bear reflect its highly carnivorous diet. The cheek teeth are smaller and more jagged than in the brown bear, and the canines are larger and sharper. The dental formula is . [31]

Polar bears are superbly insulated by up to 10 cm (4 in) of adipose tissue, [60] their hide and their fur. Polar bear fur consists of a layer of dense underfur and an outer layer of guard hairs, which appear white to tan but are actually transparent. [60] Two genes that are known to influence melanin production, LYST and AIM1, are both mutated in polar bears, possibly leading to the absence on this pigment in their fur. [62] The guard hair is 5–15 cm (2–6 in) over most of the body. [63] Polar bears gradually moult from May to August, [64] but, unlike other Arctic mammals, they do not shed their coat for a darker shade to provide camouflage in summer conditions. [65] The hollow guard hairs of a polar bear coat were once thought to act as fiber-optic tubes to conduct light to its black skin, where it could be absorbed however, this hypothesis was disproved by a study in 1998. [66]

The white coat usually yellows with age. When kept in captivity in warm, humid conditions, the fur may turn a pale shade of green due to algae growing inside the guard hairs. [67] Males have significantly longer hairs on their forelegs, which increase in length until the bear reaches 14 years of age. The male's ornamental foreleg hair is thought to attract females, serving a similar function to the lion's mane. [68]

The polar bear has an extremely well developed sense of smell, being able to detect seals nearly 1.6 km (1 mi) away and buried under 1 m (3 ft) of snow. Its hearing is about as acute as that of a human, and its vision is also good at long distances. [69]

The polar bear is an excellent swimmer and often will swim for days. [70] One bear swam continuously for 9 days in the frigid Bering Sea for 700 km (400 mi) to reach ice far from land. She then travelled another 1,800 km (1,100 mi). During the swim, the bear lost 22% of her body mass and her yearling cub died. [71] With its body fat providing buoyancy, the bear swims in a dog paddle fashion using its large forepaws for propulsion. Polar bears can swim at 10 km/h (6 mph). When walking, the polar bear tends to have a lumbering gait and maintains an average speed of around 5.6 km/h (3.5 mph). [72] When sprinting, they can reach up to 40 km/h (25 mph). [73]

Unlike brown bears, polar bears are not territorial. Although stereotyped as being voraciously aggressive, they are normally cautious in confrontations, and often choose to escape rather than fight. [74] Satiated polar bears rarely attack humans unless severely provoked. [75] [76] However, due to their lack of prior human interaction, hungry polar bears are extremely unpredictable, fearless towards people and are known to kill and sometimes eat humans. [77] Many attacks by brown bears are the result of surprising the animal, which is not the case with the polar bear. Polar bears are stealth hunters, and the victim is often unaware of the bear's presence until the attack is underway. Whereas brown bears often maul a person and then leave, polar bear attacks are more likely to be predatory and are almost always fatal. [78] However, due to the very small human population around the Arctic, such attacks are rare. Michio Hoshino, a Japanese wildlife photographer, was once pursued briefly by a hungry male polar bear in northern Alaska. According to Hoshino, the bear started running but Hoshino made it to his truck. The bear was able to reach the truck and tore one of the doors off the truck before Hoshino was able to drive off. [79]

In general, adult polar bears live solitary lives. Yet, they have often been seen playing together for hours at a time and even sleeping in an embrace, [77] and polar bear zoologist Nikita Ovsianikov has described adult males as having "well-developed friendships." [74] Cubs are especially playful as well. Among young males in particular, play-fighting may be a means of practicing for serious competition during mating seasons later in life. [80] Polar bears are usually quiet but do communicate with various sounds and vocalizations. Females communicate with their young with moans and chuffs, and the distress calls of both cubs and subadults consists of bleats. [81] Cubs may hum while nursing. [82] When nervous, bears produce huffs, chuffs and snorts while hisses, growls and roars are signs of aggression. [81] Chemical communication can also be important: bears leave behind their scent in their tracks which allow individuals to keep track of one another in the vast Arctic wilderness. [83]

In 1992, a photographer near Churchill took a now widely circulated set of photographs of a polar bear playing with a Canadian Eskimo Dog (Canis lupus familiaris) a tenth of its size. [84] [85] The pair wrestled harmlessly together each afternoon for 10 days in a row for no apparent reason, although the bear may have been trying to demonstrate its friendliness in the hope of sharing the kennel's food. This kind of social interaction is uncommon it is far more typical for polar bears to behave aggressively towards dogs. [84]

Hunting and diet

The polar bear is the most carnivorous member of the bear family, and throughout most of its range, its diet primarily consists of ringed (Pusa hispida) and bearded seals (Erignathus barbatus). [87] The Arctic is home to millions of seals, which become prey when they surface in holes in the ice in order to breathe, or when they haul out on the ice to rest. [86] [88] Polar bears hunt primarily at the interface between ice, water, and air they only rarely catch seals on land or in open water. [89]

The polar bear's most common hunting method is called still-hunting: [90] the bear uses its excellent sense of smell to locate a seal breathing hole, and crouches nearby in silence for a seal to appear. The bear may lie in wait for several hours. When the seal exhales, the bear smells its breath, reaches into the hole with a forepaw, and drags it out onto the ice. The polar bear kills the seal by biting its head to crush its skull. The polar bear also hunts by stalking seals resting on the ice: upon spotting a seal, it walks to within 90 m (100 yd), and then crouches. If the seal does not notice, the bear creeps to within 9 to 12 m (30 to 40 ft) of the seal and then suddenly rushes forth to attack. [86] A third hunting method is to raid the birth lairs that female seals create in the snow. [90]

A widespread legend tells that polar bears cover their black noses with their paws when hunting. This behaviour, if it happens, is rare – although the story exists in the oral history of northern peoples and in accounts by early Arctic explorers, there is no record of an eyewitness account of the behaviour in recent decades. [72]

Mature bears tend to eat only the calorie-rich skin and blubber of the seal, which are highly digestible, [91] whereas younger bears consume the protein-rich red meat. [86] Studies have also photographed polar bears scaling near-vertical cliffs, to eat birds' chicks and eggs. [92] For subadult bears, which are independent of their mother but have not yet gained enough experience and body size to successfully hunt seals, scavenging the carcasses from other bears' kills is an important source of nutrition. Subadults may also be forced to accept a half-eaten carcass if they kill a seal but cannot defend it from larger polar bears. After feeding, polar bears wash themselves with water or snow. [72]

Although polar bears are extraordinarily powerful, its primary prey species, the ringed seal, is much smaller than itself, and many of the seals hunted are pups rather than adults. Ringed seals are born weighing 5.4 kg (12 lb) and grown to an estimated average weight of only 60 kg (130 lb). [93] [94] They also in places prey heavily upon the harp seal (Pagophilus groenlandicus), the harbour seal (Phoca vitulina), or the hooded seal (Cystophora cristata). [95] The bearded seal, on the other hand, can be nearly the same size as the bear itself, averaging 270 kg (600 lb). [94] Adult male bearded seals, at 350 to 500 kg (770 to 1,100 lb) are too large for a female bear to overtake, and so are potential prey only for mature male bears. [96] Large males also occasionally attempt to hunt and kill even larger prey items. [97] It can kill an adult walrus (Odobenus rosmarus), [94] [98] although this is rarely attempted. At up to 2,000 kg (4,400 lb) and a typical adult mass range of 600 to 1,500 kg (1,300 to 3,300 lb), a walrus can be more than twice the bear's weight, [99] has extremely thick skin and has up to 1-metre (3 ft)-long ivory tusks that can be used as formidable weapons. A polar bear may charge a group of walruses, with the goal of separating a young, infirm, or injured walrus from the pod. They will even attack adult walruses when their diving holes have frozen over or intercept them before they can get back to the diving hole in the ice. Yet, polar bears will very seldom attack full-grown adult walruses, with the largest male walrus probably invulnerable unless otherwise injured or incapacitated. Since an attack on a walrus tends to be an extremely protracted and exhausting venture, bears have been known to back down from the attack after making the initial injury to the walrus. [98] Polar bears have also been seen to prey on beluga whales (Delphinapterus leucas) [94] and narwhals (Monodon monoceros), [94] by swiping at them at breathing holes. The whales are of similar size to the walrus and nearly as difficult for the bear to subdue. [100] [101] Most terrestrial animals in the Arctic can outrun the polar bear on land as polar bears overheat quickly, and most marine animals the bear encounters can outswim it. In some areas, the polar bear's diet is supplemented by walrus calves and by the carcasses of dead adult walruses or whales, whose blubber is readily devoured even when rotten. [77] Polar bears sometimes swim underwater to catch fish like the Arctic charr or the fourhorn sculpin. [88]

With the exception of pregnant females, polar bears are active year-round, although they have a vestigial hibernation induction trigger in their blood. Unlike brown and black bears, polar bears are capable of fasting for up to several months during late summer and early fall, when they cannot hunt for seals because the sea is unfrozen. [102] When sea ice is unavailable during summer and early autumn, some populations live off fat reserves for months at a time, [103] as polar bears do not 'hibernate' any time of the year. [104]

Being both curious animals and scavengers, [99] [105] polar bears investigate and consume garbage where they come into contact with humans. [94] [99] Polar bears may attempt to consume almost anything they can find, including hazardous substances such as styrofoam, plastic, car batteries, ethylene glycol, hydraulic fluid, and motor oil. [99] [105] The dump in Churchill, Manitoba was closed in 2006 to protect bears, and waste is now recycled or transported to Thompson, Manitoba. [106] [107]

Dietary flexibility

Although seal predation is the primary and an indispensable way of life for most polar bears, when alternatives are present they are quite flexible. Polar bears consume a wide variety of other wild foods, including muskox (Ovibos moschatus), reindeer (Rangifer tarandus), birds, eggs, rodents, crabs, other crustaceans, fish [95] and other polar bears. They may also eat plants, including berries, roots, and kelp [108] however, none of these have been a significant part of their diet, [99] except for beachcast marine mammal carcasses. Given the change in climate, with ice breaking up in areas such as the Hudson Bay earlier than it used to, polar bears are exploiting food resources such as snow geese and eggs, and plants such as lyme grass in increased quantities. [109]

When stalking land animals, such as muskox, reindeer, [108] and even willow ptarmigan (Lagopus lagopus), polar bears appear to make use of vegetative cover and wind direction to bring them as close to their prey as possible before attacking. Polar bears have been observed to hunt the small Svalbard reindeer (R. t. platyrhynchus), which weigh only 40 to 60 kg (90 to 130 lb) as adults, as well as the barren-ground caribou (R. t. groenlandicus), which is about twice as heavy as the former. [110] [111] Adult muskox, which can weigh 450 kg (1,000 lb) or more, are a more formidable quarry. [112] Although ungulates are not typical prey, the killing of one during the summer months can greatly increase the odds of survival during that lean period. Like the brown bear, most ungulate prey of polar bears is likely to be young, sickly or injured specimens rather than healthy adults. [111] The polar bear's metabolism is specialized to require large amounts of fat from marine mammals, and it cannot derive sufficient caloric intake from terrestrial food. [113] [114]

In their southern range, especially near Hudson Bay and James Bay, Canadian polar bears endure all summer without sea ice to hunt from. [108] Here, their food ecology shows their dietary flexibility. They still manage to consume some seals, but they are food-deprived in summer as only marine mammal carcasses are an important alternative without sea ice, especially carcasses of the beluga whale. These alternatives may reduce the rate of weight loss of bears when on land. [115] One scientist found that 71% of the Hudson Bay bears had fed on seaweed (marine algae) and that about half were feeding on birds [94] such as the dovekie and sea ducks, especially the long-tailed duck (53%) and common eider, by swimming underwater to catch them. They were also diving to feed on blue mussels and other underwater food sources like the green sea urchin. 24% had eaten moss recently, 19% had consumed grass, 34% had eaten black crowberry and about half had consumed willows. [108] This study illustrates the polar bear's dietary flexibility but it does not represent its life history elsewhere. Most polar bears elsewhere will never have access to these alternatives, except for the marine mammal carcasses that are important wherever they occur.

In Svalbard, polar bears were observed to kill white-beaked dolphins during spring, when the dolphins were trapped in the sea ice. The bears then proceeded to cache the carcasses, which remained and were eaten during the ice-free summer and autumn. [116]

Reproduction and lifecycle

Courtship and mating take place on the sea ice in April and May, when polar bears congregate in the best seal hunting areas. [117] A male may follow the tracks of a breeding female for 100 km (60 mi) or more, and after finding her engage in intense fighting with other males over mating rights, fights that often result in scars and broken teeth. [117] Polar bears have a generally polygynous mating system recent genetic testing of mothers and cubs, however, has uncovered cases of litters in which cubs have different fathers. [118] Partners stay together and mate repeatedly for an entire week the mating ritual induces ovulation in the female. [119]

After mating, the fertilized egg remains in a suspended state until August or September. During these four months, the pregnant female eats prodigious amounts of food, gaining at least 200 kg (440 lb) and often more than doubling her body weight. [117]

Maternity denning and early life

When the ice floes are at their minimum in the fall, ending the possibility of hunting, each pregnant female digs a maternity den consisting of a narrow entrance tunnel leading to one to three chambers. Most maternity dens are in snowdrifts, but may also be made underground in permafrost if it is not sufficiently cold yet for snow. [117] In most subpopulations, maternity dens are situated on land a few kilometres from the coast, and the individuals in a subpopulation tend to reuse the same denning areas each year. [36] The polar bears that do not den on land make their dens on the sea ice. In the den, she enters a dormant state similar to hibernation. This hibernation-like state does not consist of continuous sleeping however, the bear's heart rate slows from 46 to 27 beats per minute. [120] Her body temperature does not decrease during this period as it would for a typical mammal in hibernation. [103] [121]

Between November and February, cubs are born blind, covered with a light down fur, and weighing less than 0.9 kg (2.0 lb), [119] but in captivity they might be delivered in the earlier months. The earliest recorded birth of polar bears in captivity was on 11 October 2011 in the Toronto Zoo. [122] On average, each litter has two cubs. The family remains in the den until mid-February to mid-April, with the mother maintaining her fast while nursing her cubs on a fat-rich milk. By the time the mother breaks open the entrance to the den, her cubs weigh about 10 to 15 kilograms (22 to 33 lb). For about 12 to 15 days, the family spends time outside the den while remaining in its vicinity, the mother grazing on vegetation while the cubs become used to walking and playing. Then they begin the long walk from the denning area to the sea ice, where the mother can once again catch seals. Depending on the timing of ice-floe breakup in the fall, she may have fasted for up to eight months. [117] During this time, cubs playfully imitate the mother's hunting methods in preparation for later life. [123]

Female polar bears have been known to adopt other cubs. Multiple cases of adoption of wild cubs have been confirmed by genetic testing. [124] Adult bears of either gender occasionally kill and eat polar bear cubs. [125] [126] As of 2006, in Alaska, 42% of cubs were reaching 12 months of age, down from 65% in 1991. [127] In most areas, cubs are weaned at two and a half years of age, when the mother chases them away or abandons them. The Western Hudson Bay subpopulation is unusual in that its female polar bears sometimes wean their cubs at only one and a half years. [117] This was the case for 40% of cubs there in the early 1980s however by the 1990s, fewer than 20% of cubs were weaned this young. [128] After the mother leaves, sibling cubs sometimes travel and share food together for weeks or months. [77]

Later life

Females begin to breed at the age of four years in most areas, and five years in the area of the Beaufort Sea. Males usually reach sexual maturity at six years however, as competition for females is fierce, many do not breed until the age of eight or ten. [117] A study in Hudson Bay indicated that both the reproductive success and the maternal weight of females peaked in their mid-teens.Maternal success appeared to decline after this point, possibly because of an age-related impairment in the ability to store the fat necessary to rear cubs. [129]

Polar bears appear to be less affected by infectious diseases and parasites than most terrestrial mammals. [130] Polar bears are especially susceptible to Trichinella, a parasitic roundworm they contract through cannibalism, [131] although infections are usually not fatal. Only one case of a polar bear with rabies has been documented, even though polar bears frequently interact with Arctic foxes, which often carry rabies. [130] Bacterial leptospirosis and Morbillivirus have been recorded. Polar bears sometimes have problems with various skin diseases that may be caused by mites or other parasites.

Life expectancy

Polar bears rarely live beyond 25 years. [132] The oldest wild bears on record died at age 32, whereas the oldest captive was a female who died in 1991, age 43. [133] The causes of death in wild adult polar bears are poorly understood, as carcasses are rarely found in the species's frigid habitat. In the wild, old polar bears eventually become too weak to catch food, and gradually starve to death. Polar bears injured in fights or accidents may either die from their injuries, or become unable to hunt effectively, leading to starvation. [130]

Ecological role

The polar bear is the apex predator within its range, and is a keystone species for the Arctic. [134] Several animal species, particularly Arctic foxes (Vulpes lagopus) and glaucous gulls (Larus hyperboreus), routinely scavenge polar bear kills. [72]

The relationship between ringed seals and polar bears is so close that the abundance of ringed seals in some areas appears to regulate the density of polar bears, while polar bear predation in turn regulates density and reproductive success of ringed seals. [89] The evolutionary pressure of polar bear predation on seals probably accounts for some significant differences between Arctic and Antarctic seals. Compared to the Antarctic, where there is no major surface predator, Arctic seals use more breathing holes per individual, appear more restless when hauled out on the ice, and rarely defecate on the ice. The baby fur of most Arctic seal species is white, presumably to provide camouflage from predators, whereas Antarctic seals all have dark fur at birth. [72]

Brown bears tend to dominate polar bears in disputes over carcasses, [135] and dead polar bear cubs have been found in brown bear dens. [136] Wolves are rarely encountered by polar bears, though there are two records of Arctic wolf (Canis lupus arctos) packs killing polar bear cubs. [137] Adult polar bears are occasionally vulnerable to predation by orcas (Orcinus orca) while swimming, but they are rarely reported as taken and bears are likely to avoid entering the water if possible if they detect an orca pod in the area. The melting sea ice in the Arctic may be causing an increase of orcas in the Arctic sea, which may increase the risk of predation on polar bears but also may benefit the bears by providing more whale carcasses that they can scavenge. [138] [139] The remains of polar bears have found in the stomachs of large Greenland sharks (Somniosus microcephalus), although it certainly cannot be ruled out that the bears were merely scavenged by this slow-moving, unusual shark. [140] [141] A rather unlikely killer of a grown polar bear has reportedly included a wolverine (Gulo gulo), anecedotely reported to have suffocated a bear in a zoo with a bite to the throat during a conflict. This report may well be dubious, however. [142] Polar bears are sometimes the host of arctic mites such as Alaskozetes antarcticus. [72]

Long-distance swimming and diving

Researchers tracked 52 sows in the southern Beaufort Sea off Alaska with GPS system collars no boars were involved in the study due to males' necks being too thick for the GPS-equipped collars. Fifty long-distance swims were recorded the longest at 354 kilometres (220 mi), with an average of 155 kilometres (96 mi). The length of these swims ranged from most of a day to ten days. Ten of the sows had a cub swim with them and after a year, six cubs survived. The study did not determine if the others lost their cubs before, during, or some time after their long swims. Researchers do not know whether or not this is a new behaviour before polar ice shrinkage, they opined that there was probably neither the need nor opportunity to swim such long distances. [143]

The polar bear may swim underwater for up to three minutes to approach seals on shore or on ice floes. [144] [145]

Indigenous people

Polar bears have long provided important raw materials for Arctic peoples, including the Inuit, Yupik, Chukchi, Nenets, Russian Pomors and others. Hunters commonly used teams of dogs to distract the bear, allowing the hunter to spear the bear or shoot it with arrows at closer range. [146] Almost all parts of captured animals had a use. [147] The fur was used in particular to make trousers and, by the Nenets, to make galoshes-like outer footwear called tobok the meat is edible, despite some risk of trichinosis the fat was used in food and as a fuel for lighting homes, alongside seal and whale blubber sinews were used as thread for sewing clothes the gallbladder and sometimes heart were dried and powdered for medicinal purposes the large canine teeth were highly valued as talismans. [148] Only the liver was not used, as its high concentration of vitamin A is poisonous. As a carnivore, which feeds largely upon fish-eating carnivores, the polar bear ingests large amounts of vitamin A that is stored in their livers. The resulting high concentrations cause Hypervitaminosis A, [149] Hunters make sure to either toss the liver into the sea or bury it in order to spare their dogs from potential poisoning. [148] Traditional subsistence hunting was on a small enough scale to not significantly affect polar bear populations, mostly because of the sparseness of the human population in polar bear habitat. [150]

History of commercial harvest

In Russia, polar bear furs were already being commercially traded in the 14th century, though it was of low value compared to Arctic fox or even reindeer fur. [148] The growth of the human population in the Eurasian Arctic in the 16th and 17th century, together with the advent of firearms and increasing trade, dramatically increased the harvest of polar bears. [103] [151] However, since polar bear fur has always played a marginal commercial role, data on the historical harvest is fragmentary. It is known, for example, that already in the winter of 1784/1785 Russian Pomors on Spitsbergen harvested 150 polar bears in Magdalenefjorden. In the early 20th century, Norwegian hunters were harvesting 300 bears per year at the same location. Estimates of total historical harvest suggest that from the beginning of the 18th century, roughly 400 to 500 animals were being harvested annually in northern Eurasia, reaching a peak of 1,300 to 1,500 animals in the early 20th century, and falling off as the numbers began dwindling. [148]

In the first half of the 20th century, mechanized and overpoweringly efficient methods of hunting and trapping came into use in North America as well. Polar bears were chased from snowmobiles, icebreakers, and airplanes, the latter practice described in a 1965 New York Times editorial as being "about as sporting as machine gunning a cow." [152] Norwegians used "self-killing guns", comprising a loaded rifle in a baited box that was placed at the level of a bear's head, and which fired when the string attached to the bait was pulled. [153] The numbers taken grew rapidly in the 1960s, peaking around 1968 with a global total of 1,250 bears that year. [154]

Contemporary regulations

Concerns over the future survival of the species led to the development of national regulations on polar bear hunting, beginning in the mid-1950s. The Soviet Union banned all hunting in 1956. Canada began imposing hunting quotas in 1968. Norway passed a series of increasingly strict regulations from 1965 to 1973, and has completely banned hunting since then. The United States began regulating hunting in 1971 and adopted the Marine Mammal Protection Act in 1972. In 1973, the International Agreement on the Conservation of Polar Bears was signed by all five nations whose territory is inhabited by polar bears: Canada, Denmark, Norway, the Soviet Union, and the United States. Member countries agreed to place restrictions on recreational and commercial hunting, ban hunting from aircraft and icebreakers, and conduct further research. [155] The treaty allows hunting "by local people using traditional methods". Norway is the only country of the five in which all harvest of polar bears is banned. The agreement was a rare case of international cooperation during the Cold War. Biologist Ian Stirling commented, "For many years, the conservation of polar bears was the only subject in the entire Arctic that nations from both sides of the Iron Curtain could agree upon sufficiently to sign an agreement. Such was the intensity of human fascination with this magnificent predator, the only marine bear." [156]

Agreements have been made between countries to co-manage their shared polar bear subpopulations. After several years of negotiations, Russia and the United States signed an agreement in October 2000 to jointly set quotas for indigenous subsistence hunting in Alaska and Chukotka. [157] The treaty was ratified in October 2007. [158] In September 2015, the polar bear range states agreed upon a "circumpolar action plan" describing their conservation strategy for polar bears. [159]

Although the United States government has proposed that polar bears be transferred to Appendix I of CITES, which would ban all international trade in polar bear parts, polar bears currently remain listed under Appendix II. [160] This decision was approved of by members of the IUCN and TRAFFIC, who determined that such an uplisting was unlikely to confer a conservation benefit. [161]


Polar bears were designated "Not at Risk" in April 1986 and uplisted to "Special Concern" in April 1991. This status was re-evaluated and confirmed in April 1999, November 2002, and April 2008. Polar bears continue to be listed as a species of special concern in Canada because of their sensitivity to overharvest and because of an expected range contraction caused by loss of Arctic sea ice. [162]

More than 600 bears are killed per year by humans across Canada, [45] a rate calculated by scientists to be unsustainable for some areas, notably Baffin Bay. [37] Canada has allowed sport hunters accompanied by local guides and dog-sled teams since 1970, [163] but the practice was not common until the 1980s. [164] The guiding of sport hunters provides meaningful employment and an important source of income for northern communities in which economic opportunities are few. [43] Sport hunting can bring CDN$20,000 to $35,000 per bear into northern communities, which until recently has been mostly from American hunters. [165]

The territory of Nunavut accounts for the location 80% of annual kills in Canada. In 2005, the government of Nunavut increased the quota from 400 to 518 bears, [165] despite protests from the IUCN Polar Bear Specialist Group. [166] In two areas where harvest levels have been increased based on increased sightings, science-based studies have indicated declining populations, and a third area is considered data-deficient. [167] While most of that quota is hunted by the indigenous Inuit people, a growing share is sold to recreational hunters. (0.8% in the 1970s, 7.1% in the 1980s, and 14.6% in the 1990s) [164] Nunavut polar bear biologist, Mitchell Taylor, who was formerly responsible for polar bear conservation in the territory, has insisted that bear numbers are being sustained under current hunting limits. [168] In 2010, the 2005 increase was partially reversed. Government of Nunavut officials announced that the polar bear quota for the Baffin Bay region would be gradually reduced from 105 per year to 65 by the year 2013. [169] The Government of the Northwest Territories maintain their own quota of 72 to 103 bears within the Inuvialuit communities of which some are set aside for sports hunters. [ citation needed ] Environment Canada also banned the export from Canada of fur, claws, skulls and other products from polar bears harvested in Baffin Bay as of 1 January 2010. [169]

Because of the way polar bear hunting quotas are managed in Canada, attempts to discourage sport hunting would actually increase the number of bears killed in the short term. Canada allocates a certain number of permits each year to sport and subsistence hunting, and those that are not used for sport hunting are re-allocated to indigenous subsistence hunting. Whereas northern communities kill all the polar bears they are permitted to take each year, only half of sport hunters with permits actually manage to kill a polar bear. If a sport hunter does not kill a polar bear before his or her permit expires, the permit cannot be transferred to another hunter. [43]

In August 2011, Environment Canada published a national polar bear conservation strategy. [170]


In Greenland, hunting restrictions were first introduced in 1994 and expanded by executive order in 2005. [39] Until 2005 Greenland placed no limit on hunting by indigenous people. However, in 2006 it imposed a limit of 150, while also allowed recreational hunting for the first time. [171] Other provisions included year-round protection of cubs and mothers, restrictions on weapons used and various administrative requirements to catalogue kills. [39]


Polar bears were hunted heavily in Svalbard, Norway throughout the 19th century and to as recently as 1973, when the conservation treaty was signed. 900 bears a year were harvested in the 1920s and after World War II, there were as many as 400–500 harvested annually. Some regulations of hunting did exist. In 1927, poisoning was outlawed while in 1939, certain denning sights were declared off limits. The killing of females and cubs was made illegal in 1965. Killing of polar bears decreased somewhat 25–30 years before the treaty. Despite this, the polar bear population continued to decline and by 1973, only around 1000 bears were left in Svalbard. Only with the passage of the treaty did they begin to recover. [172]


The Soviet Union banned the harvest of polar bears in 1956 however, poaching continued, and is estimated to pose a serious threat to the polar bear population. [39] In recent years, polar bears have approached coastal villages in Chukotka more frequently due to the shrinking of the sea ice, endangering humans and raising concerns that illegal hunting would become even more prevalent. In 2007, the Russian government made subsistence hunting legal for indigenous Chukotkan peoples only, a move supported by Russia's most prominent bear researchers and the World Wide Fund for Nature as a means to curb poaching. [173]

Polar bears are currently listed as "Rare", of "Uncertain Status", or "Rehabilitated and rehabilitating" in the Red Data Book of Russia, depending on population. [174] In 2010, the Ministry of Natural Resources and Environment published a strategy for polar bear conservation in Russia. [175]

United States

The Marine Mammal Protection Act of 1972 afforded polar bears some protection in the United States. It banned hunting (except by indigenous subsistence hunters), banned importing of polar bear parts (except polar bear pelts taken legally in Canada), and banned the harassment of polar bears. On 15 May 2008, the United States Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act, citing the melting of Arctic sea ice as the primary threat to the polar bear. [176] It banned all importing of polar bear trophies. Importing products made from polar bears had been prohibited from 1972 to 1994 under the Marine Mammal Protection Act, and restricted between 1994 and 2008. Under those restrictions, permits from the United States Fish and Wildlife Service were required to import sport-hunted polar bear trophies taken in hunting expeditions in Canada. The permit process required that the bear be taken from an area with quotas based on sound management principles. [177] Since 1994, hundreds of sport-hunted polar bear trophies have been imported into the U.S. [178] In 2015, the U.S. Fish and Wildlife Service published a draft conservation management plan for polar bears to improve their status under the Endangered Species Act and the Marine Mammal Protection Act. [179]

Polar bear population sizes and trends are difficult to estimate accurately because they occupy remote home ranges and exist at low population densities. Polar bear fieldwork can also be hazardous to researchers. [180] As of 2015, the International Union for Conservation of Nature (IUCN) reports that the global population of polar bears is 22,000 to 31,000, and the current population trend is unknown. Nevertheless, polar bears are listed as "Vulnerable" under criterion A3c, which indicates an expected population decrease of ≥30% over the next three generations (

34.5 years) due to "decline in area of occupancy, extent of occurrence and/or quality of habitat". Risks to the polar bear include climate change, pollution in the form of toxic contaminants, conflicts with shipping, oil and gas exploration and development, and human-bear interactions including harvesting and possible stresses from recreational polar-bear watching. [2]

According to the World Wildlife Fund, the polar bear is important as an indicator of Arctic ecosystem health. Polar bears are studied to gain understanding of what is happening throughout the Arctic, because at-risk polar bears are often a sign of something wrong with the Arctic marine ecosystem. [181]

Climate change

The International Union for Conservation of Nature, Arctic Climate Impact Assessment, United States Geological Survey and many leading polar bear biologists have expressed grave concerns about the impact of climate change, with some predicting extinction by 2100. [182]

The key danger posed by climate change is malnutrition or starvation due to habitat loss. Polar bears hunt seals from a platform of sea ice. Rising temperatures cause the sea ice to melt earlier in the year, driving the bears to shore before they have built sufficient fat reserves to survive the period of scarce food in the late summer and early fall. [128] Reduction in sea-ice cover also forces bears to swim longer distances, which further depletes their energy stores and occasionally leads to drowning. [183] Thinner sea ice tends to deform more easily, which appears to make it more difficult for polar bears to access seals. [89] Insufficient nourishment leads to lower reproductive rates in adult females and lower survival rates in cubs and juvenile bears, in addition to poorer body condition in bears of all ages. [36]

In addition to creating nutritional stress, a warming climate is expected to affect various other aspects of polar bear life: changes in sea ice affect the ability of pregnant females to build suitable maternity dens. [30] As the distance increases between the pack ice and the coast, females must swim longer distances to reach favoured denning areas on land. Thawing of permafrost would affect the bears who traditionally den underground, and warm winters could result in den roofs collapsing or having reduced insulative value. For the polar bears that currently den on multi-year ice, increased ice mobility may result in longer distances for mothers and young cubs to walk when they return to seal-hunting areas in the spring. [36] Disease-causing bacteria and parasites would flourish more readily in a warmer climate. [89]

Problematic interactions between polar bears and humans, such as foraging by bears in garbage dumps, have historically been more prevalent in years when ice-floe breakup occurred early and local polar bears were relatively thin. Increased human-bear interactions, including fatal attacks on humans, are likely to increase as the sea ice shrinks and hungry bears try to find food on land. [184]

The effects of climate change are most profound in the southern part of the polar bear's range, and this is indeed where significant degradation of local populations has been observed. [185] The Western Hudson Bay subpopulation, in a southern part of the range, also happens to be one of the best-studied polar bear subpopulations. This subpopulation feeds heavily on ringed seals in late spring, when newly weaned and easily hunted seal pups are abundant. The late spring hunting season ends for polar bears when the ice begins to melt and break up, and they fast or eat little during the summer until the sea freezes again. [167]

Due to warming air temperatures, ice-floe breakup in western Hudson Bay is currently occurring three weeks earlier than it did 30 years ago, reducing the duration of the polar bear feeding season. The body condition of polar bears has declined during this period the average weight of lone (and likely pregnant) female polar bears was approximately 290 kg (640 lb) in 1980 and 230 kg (510 lb) in 2004. [167] Between 1987 and 2004, the Western Hudson Bay population declined by 22%, [186] although the population was listed as "stable" as of 2017. [45] As the climate change melts sea ice, the U.S. Geological Survey projects that two-thirds of polar bears will disappear by 2050. [187]

In Alaska, the effects of sea ice shrinkage have contributed to higher mortality rates in polar bear cubs, and have led to changes in the denning locations of pregnant females. [127] The proportion of maternity dens on sea ice has changed from 62% between the years 1985 through 1994, to 37% over the years 1998 through 2004. Thus, now the Alaskan population more resembles the world population in that it is more likely to den on land. [188] In recent years, polar bears in the Arctic have undertaken longer than usual swims to find prey, possibly resulting in four recorded drownings in the unusually large ice pack regression of 2005. [183]

A new development is that polar bears have begun ranging to new territory. While not unheard of but still uncommon, polar bears have been sighted increasingly in larger numbers ashore, staying on the mainland for longer periods of time during the summer months, particularly in North Canada, traveling farther inland. [189] This may cause an increased reliance on terrestrial diets, such as goose eggs, waterfowl and caribou, [190] as well as increased human–bear conflict. [189]


Polar bears accumulate high levels of persistent organic pollutants such as polychlorinated biphenyl (PCBs) and chlorinated pesticides. Due to their position at the top of the ecological pyramid, with a diet heavy in blubber in which halocarbons concentrate, their bodies are among the most contaminated of Arctic mammals. [191] Halocarbons (also known as organohalogens) are known to be toxic to other animals, because they mimic hormone chemistry, and biomarkers such as immunoglobulin G and retinol suggest similar effects on polar bears. PCBs have received the most study, and they have been associated with birth defects and immune system deficiency. [192]

Many chemicals, such as PCBs and DDT, have been internationally banned due to the recognition of their harm on the environment. Their concentrations in polar bear tissues continued to rise for decades after being banned, as these chemicals spread through the food chain. Since then, the trend seems to have abated, with tissue concentrations of PCBs declining between studies performed from 1989 to 1993 and studies performed from 1996 to 2002. During the same time periods, DDT was found to be notably lower in the Western Hudson Bay population only. [193]

Oil and gas development

Oil and gas development in polar bear habitat can affect the bears in a variety of ways. An oil spill in the Arctic would most likely concentrate in the areas where polar bears and their prey are also concentrated, such as sea ice leads. [2] Because polar bears rely partly on their fur for insulation and soiling of the fur by oil reduces its insulative value, oil spills put bears at risk of dying from hypothermia. Polar bears exposed to oil spill conditions have been observed to lick the oil from their fur, leading to fatal kidney failure. [102] Maternity dens, used by pregnant females and by females with infants, can also be disturbed by nearby oil exploration and development. Disturbance of these sensitive sites may trigger the mother to abandon her den prematurely, or abandon her litter altogether. [2]


Steven Amstrup and other U.S. Geological Survey scientists have predicted two-thirds of the world's polar bears may disappear by 2050, based on moderate projections for the shrinking of summer sea ice caused by climate change, [89] [187] though the validity of this study has been debated. [194] [195] The bears could disappear from Europe, Asia, and Alaska, and be depleted from the Canadian Arctic Archipelago and areas off the northern Greenland coast. By 2080, they could disappear from Greenland entirely and from the northern Canadian coast, leaving only dwindling numbers in the interior Arctic Archipelago. [89] However, in the short term, some polar bear populations in historically colder regions of the Arctic may temporarily benefit from a milder climate, as multiyear ice that is too thick for seals to create breathing holes is replaced by thinner annual ice. [196]

Polar bears diverged from brown bears 400,000–600,000 years ago and have survived past periods of climate fluctuation. It has been claimed that polar bears will be able to adapt to terrestrial food sources as the sea ice they use to hunt seals disappears. [197] However, most polar bear biologists think that polar bears will be unable to completely offset the loss of calorie-rich seal blubber with terrestrial foods, and that they will be outcompeted by brown bears in this terrestrial niche, ultimately leading to a population decline. [198]

Controversy over species protection

Warnings about the future of the polar bear are often contrasted with the fact that worldwide population estimates have increased over the past 50 years and are relatively stable today. [199] [200] Some estimates of the global population are around 5,000 to 10,000 in the early 1970s [201] other estimates were 20,000 to 40,000 during the 1980s. [48] [103] Current estimates put the global population at between 20,000 and 25,000 [39] or 22,000 and 31,000. [2]

There are several reasons for the apparent discordance between past and projected population trends: estimates from the 1950s and 1960s were based on stories from explorers and hunters rather than on scientific surveys. [202] [203] [204] [205] Second, controls of harvesting were introduced that allowed this previously overhunted species to recover. Third, the recent effects of climate change have affected sea ice abundance in different areas to varying degrees. [202]

Debate over the listing of the polar bear under endangered species legislation has put conservation groups and Canada's Inuit at opposing positions [43] the Nunavut government and many northern residents have condemned the U.S. initiative to list the polar bear under the Endangered Species Act. [206] [207] Many Inuit believe the polar bear population is increasing, and restrictions on commercial sport-hunting are likely to lead to a loss of income to their communities. [43] [208]

Indigenous folklore

For the indigenous peoples of the Arctic, polar bears have long played an important cultural and material role. [147] [148] Polar bear remains have been found at hunting sites dating to 2,500 to 3,000 years ago [150] and 1,500-year-old cave paintings of polar bears have been found in the Chukchi Peninsula. Indeed, it has been suggested that Arctic peoples' skills in seal hunting and igloo construction has been in part acquired from the polar bears themselves. [148]

The Inuit and Alaska Natives have many folk tales featuring the bears including legends in which bears are humans when inside their own houses and put on bear hides when going outside, and stories of how the constellation that is said to resemble a great bear surrounded by dogs came into being. These legends reveal a deep respect for the polar bear, which is portrayed as both spiritually powerful and closely akin to humans. The human-like posture of bears when standing and sitting, and the resemblance of a skinned bear carcass to the human body, have probably contributed to the belief that the spirits of humans and bears were interchangeable. [146]

Among the Chukchi and Yupik of eastern Siberia, there was a longstanding shamanistic ritual of "thanksgiving" to the hunted polar bear. After killing the animal, its head and skin were removed and cleaned and brought into the home, and a feast was held in the hunting camp in its honor. To appease the spirit of the bear, traditional song and drum music was played, and the skull was ceremonially fed and offered a pipe. [209] Only once the spirit was appeased was the skull be separated from the skin, taken beyond the bounds of the homestead, and placed in the ground, facing north. [148]

The Nenets of north-central Siberia placed particular value on the talismanic power of the prominent canine teeth. These were traded in the villages of the lower Yenisei and Khatanga rivers to the forest-dwelling peoples further south, who would sew them into their hats as protection against brown bears. It was believed that the "little nephew" (the brown bear) would not dare to attack a man wearing the tooth of its powerful "big uncle", the polar bear. The skulls of killed polar bears were buried at sacred sites, and altars, called sedyangi, were constructed out of the skulls. Several such sites have been preserved on the Yamal Peninsula. [148]

Symbols and mascots

Their distinctive appearance and their association with the Arctic have made polar bears popular icons, especially in those areas where they are native. The Canadian two-dollar coin carries an image of a lone polar bear on its reverse side, while a special millennium edition featured three. [210] Vehicle licence plates in the Northwest Territories in Canada are in the shape of a polar bear, as was the case in Nunavut until 2012 these now display polar bear artwork instead. [211] The polar bear is the mascot of Bowdoin College, Maine the University of Alaska Fairbanks and the 1988 Winter Olympics held in Calgary. [212] [213] [214] The Eisbären Berlin hockey team uses a roaring polar bear as their logo, and the Charlotte, North Carolina hockey team the Charlotte Checkers uses a polar bear named Chubby Checker as their mascot. [215]

Coca-Cola has used images of the polar bear in its advertising, [216] and Polar Beverages, Nelvana, Bundaberg Rum, Klondike bars, and Fox's Glacier Mints all feature polar bears in their logos.


Polar bears are popular in fiction, particularly in books for children or teenagers. For example, The Polar Bear Son is adapted from a traditional Inuit tale. [217] The animated television series Noah's Island features a polar bear named Noah as the protagonist. Polar bears feature prominently in East (North Child in the UK) by Edith Pattou, [218] The Bear by Raymond Briggs (adapted into an animated short in 1998), [219] and Chris d'Lacey's The Fire Within series. [220] The panserbjørne of Philip Pullman's fantasy trilogy His Dark Materials are sapient, dignified polar bears who exhibit anthropomorphic qualities, and feature prominently in the 2007 film adaptation of The Golden Compass. [221] The television series Lost features polar bears living on the tropical island setting. [222]

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How do polar bears act when they are in a really hot environment? anon322467 February 27, 2013

Albino polar bears look like black bears, but they aren't, they're black polar bears! anon241840 yesterday

No, polar bears are brown! They turn yellow during the cold season, and then molt when summer comes. anon60687 January 15, 2010

Contrary to what Al Gore says, polar bears are also great swimmers. It is not uncommon for a polar bear to swim as much as 100 miles while hunting.

While we're on the subject, the polar ice caps are not melting! That is junk science that is being put forth by Al Gore in order to justify those bogus carbon taxes. Polar bears are not dying off in large numbers, or drowning due to the melting ice caps either.

Nasa photos reveal that the polar ice caps shift as part of a natural cycle. The ice caps expand and contract in this dynamic cycle. Polar bears numbers have actually increased dramatically within the last three decades. anon60532 January 14, 2010

i find it disgustingly depressing that people don't believe in evolution and that they think atheists created this massive hoax. i am religious but I'm not an idiot. evolution is a fact and you cannot deny it.

i think people who regret the knowledge that science has led to are just fearful of their god and ignorant that not everything you read is real. keep on living in your fairy tale world. NeverTheLess January 13, 2010

While on the subject of polar bears, I told you not to eat that, didn't I?

Polar bear liver is toxic. Just research polar bear liver to see the facts. anon60352 January 13, 2010

Ever think, maybe God just made them this way as he knew they going to live in very cold weather? anon60334 January 13, 2010

Polar bears did not "evolve" as you stated. Indeed, "evolution" is a hoax perpetuated by atheists who stupidly reject the existence of God who created all life forms, created the Big Bang, and created all time, space and gravity laws. anon25792 February 3, 2009


Sea ice does not simply grow and melt. During its lifespan, it is very dynamic. Due to the combined action of winds, currents, water temperature, and air temperature fluctuations, sea ice expanses typically undergo a significant amount of deformation. Sea ice is classified according to whether or not it is able to drift, and according to its age.

Fast ice versus drift (or pack) ice Edit

Sea ice can be classified according to whether or not it is attached (or frozen) to the shoreline (or between shoals or to grounded icebergs). If attached, it is called landfast ice, or more often, fast ice (from fastened). Alternatively, and unlike fast ice, drift ice occurs further offshore in very wide areas, and encompasses ice that is free to move with currents and winds. The physical boundary between fast ice and drift ice is the fast ice boundary. The drift ice zone may be further divided into a shear zone, a marginal ice zone and a central pack. [4] Drift ice consists of floes, individual pieces of sea ice 20 metres (66 ft) or more across. There are names for various floe sizes: small – 20 to 100 m (66 to 328 ft) medium – 100 to 500 m (330 to 1,640 ft) big – 500 to 2,000 m (1,600 to 6,600 ft) vast – 2 to 10 kilometres (1.2 to 6.2 mi) and giant – more than 10 km (6.2 mi). [5] [6] The term pack ice is used either as a synonym to drift ice, [5] or to designate drift ice zone in which the floes are densely packed. [5] [6] [7] The overall sea ice cover is termed the ice canopy from the perspective of submarine navigation. [6] [7]

Classification based on age Edit

Another classification used by scientists to describe sea ice is based on age, that is, on its development stages. These stages are: new ice, nilas, young ice, first-year and old. [5] [6] [7]

New ice, nilas and young ice Edit

New ice is a general term used for recently frozen sea water that does not yet make up solid ice. It may consist of frazil ice (plates or spicules of ice suspended in water), slush (water saturated snow), or shuga (spongy white ice lumps a few centimeters across). Other terms, such as grease ice and pancake ice, are used for ice crystal accumulations under the action of wind and waves. [ citation needed ] When sea ice begins to form on a beach with a light swell, ice eggs up to the size of a football can be created. [8]

Nilas designates a sea ice crust up to 10 centimetres (3.9 in) in thickness. It bends without breaking around waves and swells. Nilas can be further subdivided into dark nilas – up to 5 cm (2.0 in) in thickness and very dark, and light nilas – over 5 cm (2.0 in) in thickness and lighter in color.

Young ice is a transition stage between nilas and first-year ice, and ranges in thickness from 10 cm (3.9 in) to 30 cm (12 in), Young ice can be further subdivided into grey ice – 10 cm (3.9 in) to 15 cm (5.9 in) in thickness, and grey-white ice – 15 cm (5.9 in) to 30 cm (12 in) in thickness. Young ice is not as flexible as nilas, but tends to break under wave action. Under compression, it will either raft (at the grey ice stage) or ridge (at the grey-white ice stage).

First-year sea ice Edit

First-year sea ice is ice that is thicker than young ice but has no more than one year growth. In other words, it is ice that grows in the fall and winter (after it has gone through the new ice – nilas – young ice stages and grows further) but does not survive the spring and summer months (it melts away). The thickness of this ice typically ranges from 0.3 m (0.98 ft) to 2 m (6.6 ft). [5] [6] [7] First-year ice may be further divided into thin (30 cm (0.98 ft) to 70 cm (2.3 ft)), medium (70 cm (2.3 ft) to 120 cm (3.9 ft)) and thick (>120 cm (3.9 ft)). [6] [7]

Old sea ice Edit

Old sea ice is sea ice that has survived at least one melting season (i.e. one summer). For this reason, this ice is generally thicker than first-year sea ice. Old ice is commonly divided into two types: second-year ice, which has survived one melting season, and multiyear ice, which has survived more than one. (In some sources, [5] old ice is more than 2-years old.) Multi-year ice is much more common in the Arctic than it is in the Antarctic. [5] [9] The reason for this is that sea ice in the south drifts into warmer waters where it melts. In the Arctic, much of the sea ice is land-locked.

Driving forces Edit

While fast ice is relatively stable (because it is attached to the shoreline or the seabed), drift (or pack) ice undergoes relatively complex deformation processes that ultimately give rise to sea ice's typically wide variety of landscapes. Wind is thought to be the main driving force along with ocean currents. [1] [5] The Coriolis force and sea ice surface tilt have also been invoked. [5] These driving forces induce a state of stress within the drift ice zone. An ice floe converging toward another and pushing against it will generate a state of compression at the boundary between both. The ice cover may also undergo a state of tension, resulting in divergence and fissure opening. If two floes drift sideways past each other while remaining in contact, this will create a state of shear.

Deformation Edit

Sea ice deformation results from the interaction between ice floes, as they are driven against each other. The end result may be of three types of features: [6] [7] 1) Rafted ice, when one piece is overriding another 2) Pressure ridges, a line of broken ice forced downward (to make up the keel) and upward (to make the sail) and 3) Hummock, an hillock of broken ice that forms an uneven surface. A shear ridge is a pressure ridge that formed under shear – it tends to be more linear than a ridge induced only by compression. [6] [7] A new ridge is a recent feature – it is sharp-crested, with its side sloping at an angle exceeding 40 degrees. In contrast, a weathered ridge is one with a rounded crest and with sides sloping at less than 40 degrees. [6] [7] Stamukhi are yet another type of pile-up but these are grounded and are therefore relatively stationary. They result from the interaction between fast ice and the drifting pack ice.

Level ice is sea ice that has not been affected by deformation, and is therefore relatively flat. [6] [7]

Leads and polynyas Edit

Leads and polynyas are areas of open water that occur within sea ice expanses even though air temperatures are below freezing, and provide a direct interaction between the ocean and the atmosphere, which is important for the wildlife. Leads are narrow and linear – they vary in width from meter to km scale. During the winter, the water in leads quickly freezes up. They are also used for navigation purposes – even when refrozen, the ice in leads is thinner, allowing icebreakers access to an easier sail path, and submarines to surface more easily. Polynyas are more uniform in size than leads and are also larger – two types are recognized: 1) Sensible-heat polynyas, caused by the upwelling of warmer water and 2) Latent-heat polynyas, resulting from persistent winds from the coastline. [5]

Aerial view showing an expanse of drift ice offshore Labrador (Eastern Canada) displaying floes of various sizes loosely packed, with open water in several networks of leads. (Scale not available.)

Aerial view showing an expanse of drift ice in southeastern Greenland, comprising loosely packed floes of various sizes, with a lead developing in the centre.(Scale not available.)

Aerial view showing an expanse of drift ice consisting mostly of water. (Scale not available.)

Close-up view inside a drift ice zone: several small rounded floes are separated from each other by slush or grease ice. (Bird at lower right for scale.)

Example of hummocky ice: an accumulation of ice blocks, here about 20 to 30 cm (7.9 to 11.8 in) in thickness (with a thin snow cover).

Field example of a pressure ridge. Only the sail (the part of the ridge above the ice surface) is shown in this photograph – the keel is more difficult to document.

Aerial view of the Chukchi Sea between Chukotka and Alaska, displaying a pattern of leads. Much of the open water inside those leads is already covered by new ice (indicated by a slightly lighter blue color)(scale not available).

Only the top layer of water needs to cool to the freezing point. [10] Convection of the surface layer involves the top 100–150 m (330–490 ft), down to the pycnocline of increased density.

In calm water, the first sea ice to form on the surface is a skim of separate crystals which initially are in the form of tiny discs, floating flat on the surface and of diameter less than 0.3 cm (0.12 in). Each disc has its c-axis vertical and grows outwards laterally. At a certain point such a disc shape becomes unstable, and the growing isolated crystals take on a hexagonal, stellar form, with long fragile arms stretching out over the surface. These crystals also have their c-axis vertical. The dendritic arms are very fragile, and soon break off, leaving a mixture of discs and arm fragments. With any kind of turbulence in the water, these fragments break up further into random-shaped small crystals which form a suspension of increasing density in the surface water, an ice type called frazil or grease ice. In quiet conditions the frazil crystals soon freeze together to form a continuous thin sheet of young ice in its early stages, when it is still transparent – that is the ice called nilas. Once nilas has formed, a quite different growth process occurs, in which water freezes on to the bottom of the existing ice sheet, a process called congelation growth. This growth process yields first-year ice.

In rough water, fresh sea ice is formed by the cooling of the ocean as heat is lost into the atmosphere. The uppermost layer of the ocean is supercooled to slightly below the freezing point, at which time tiny ice platelets (frazil ice) form. With time, this process leads to a mushy surface layer, known as grease ice. Frazil ice formation may also be started by snowfall, rather than supercooling. Waves and wind then act to compress these ice particles into larger plates, of several meters in diameter, called pancake ice. These float on the ocean surface, and collide with one another, forming upturned edges. In time, the pancake ice plates may themselves be rafted over one another or frozen together into a more solid ice cover, known as consolidated pancake ice. Such ice has a very rough appearance on top and bottom.

If sufficient snow falls on sea ice to depress the freeboard below sea level, sea water will flow in and a layer of ice will form of mixed snow/sea water. This is particularly common around Antarctica.

Russian scientist Vladimir Vize (1886–1954) devoted his life to study the Arctic ice pack and developed the Scientific Prediction of Ice Conditions Theory, for which he was widely acclaimed in academic circles. He applied this theory in the field in the Kara Sea, which led to the discovery of Vize Island.

The annual freeze and melt cycle is set by the annual cycle of solar insolation and of ocean and atmospheric temperature, and of variability in this annual cycle.

In the Arctic, the area of ocean covered by sea ice increases over winter from a minimum in September to a maximum in March or sometimes February, before melting over the summer. In the Antarctic, where the seasons are reversed, the annual minimum is typically in February and the annual maximum in September or October, and the presence of sea ice abutting the calving fronts of ice shelves has been shown to influence glacier flow and potentially the stability of the Antarctic ice sheet. [12] [13]

The growth and melt rate are also affected by the state of the ice itself. During growth, the ice thickening due to freezing (as opposed to dynamics) is itself dependent on the thickness, so that the ice growth slows as the ice thickens. [5] Likewise, during melt, thinner sea ice melts faster. This leads to different behaviour between multiyear and first year ice. In addition, melt ponds on the ice surface during the melt season lower the albedo such that more solar radiation is absorbed, leading to a feedback where melt is accelerated. The presence of melt ponds is affected by the permeability of the sea ice- i.e. whether meltwater can drain- and the topography of the sea ice surface, i.e. the presence of natural basins for the melt ponds to form in. First year ice is flatter than multiyear ice due to the lack of dynamic ridging, so ponds tend to have greater area. They also have lower albedo since they are on thinner ice, which blocks less of the solar radiation from reaching the dark ocean below. [14]

Changes in sea ice conditions are best demonstrated by the rate of melting over time. A composite record of Arctic ice demonstrates that the floes' retreat began around 1900, experiencing more rapid melting beginning within the past 50 years. [ citation needed ] Satellite study of sea ice began in 1979, and became a much more reliable measure of long-term changes in sea ice. In comparison to the extended record, the sea-ice extent in the polar region by September 2007 was only half the recorded mass that had been estimated to exist within the 1950–1970 period. [15]

Arctic sea ice extent ice hit an all-time low in September 2012, when the ice was determined to cover only 24% of the Arctic Ocean, offsetting the previous low of 29% in 2007. Predictions of when the first "ice free" Arctic summer might occur vary.

Antarctic sea ice extent gradually increased in the period of satellite observations, which began in 1979, until a rapid decline in southern hemisphere spring of 2016.

Sea ice provides an ecosystem for various polar species, particularly the polar bear, whose environment is being threatened as global warming causes the ice to melt more as the Earth's temperature gets warmer. Furthermore, the sea ice itself functions to help keep polar climates cool, since the ice exists in expansive enough amounts to maintain a cold environment. At this, sea ice's relationship with global warming is cyclical the ice helps to maintain cool climates, but as the global temperature increases, the ice melts, and is less effective in keeping those climates cold. The bright, shiny surface (albedo) of the ice also serves a role in maintaining cooler polar temperatures by reflecting much of the sunlight that hits it back into space. As the sea ice melts, its surface area shrinks, diminishing the size of the reflective surface and therefore causing the earth to absorb more of the sun's heat. As the ice melts it lowers the albedo thus causing more heat to be absorbed by the Earth and further increase the amount of melting ice. [16] Though the size of the ice floes is affected by the seasons, even a small change in global temperature can greatly affect the amount of sea ice, and due to the shrinking reflective surface that keeps the ocean cool, this sparks a cycle of ice shrinking and temperatures warming. As a result, the polar regions are the most susceptible places to climate change on the planet. [5]

Furthermore, sea ice affects the movement of ocean waters. In the freezing process, much of the salt in ocean water is squeezed out of the frozen crystal formations, though some remains frozen in the ice. This salt becomes trapped beneath the sea ice, creating a higher concentration of salt in the water beneath ice floes. This concentration of salt contributes to the salinated water's density, and this cold, denser water sinks to the bottom of the ocean. This cold water moves along the ocean floor towards the equator, while warmer water on the ocean surface moves in the direction of the poles. This is referred to as "conveyor belt motion", and is a regularly occurring process. [5]

Change in extent of the Arctic Sea ice between April and August, in 2013.


Polar bears (Ursus maritimus) are heavily dependent on marine prey, in particular ice-associated seals, which they hunt on landfast sea ice or free-floating pack ice. Dramatic current (and predicted) losses of sea ice habitat make it increasingly important to gain more knowledge of the relative use by bears of all types of prey from the marine food web as well as from terrestrial sources. This study uses frequency of occurrence of food items in 119 polar bear scats sampled on the sea ice as well as on shore in coastal areas in the Svalbard Archipelago, mainly in spring, between 2003 and 2010 to explore the diet of bears in the region. Ringed seals (Pusa hispida) occurred in 62.2 % (CI 52.8–70.9 %) of the scat samples examined. Various terrestrial plants (32.8 %, CI 24.4–42.0 %) and marine algae (21.8 %, CI 14.8–30.4 %) also occurred frequently in the scats the significance of this high occurrence of plants and algae is not clear. Bearded seals (Erignathus barbatus) and various bird species constituted only minor components of the diet, while Svalbard reindeer (Rangifer tarandus platyrhynchus) occurred in 9.2 % (CI 4.7–15.9 %) of the scats, indicating that this species may play a more important role than previously reported. The novel combination of genetic analyses of material in the fecal samples along with detailed exploration of the physical–structural properties of prey hairs and plant parts provided a much fuller picture of the diet of polar bears than would have been possible from observational studies of polar bear predation behavior alone. This approach may provide an important tool for monitoring the responses of polar bears to ongoing ecosystem changes that will result from continued warming in the Arctic.
Polar bears primarily hunt ice-associated seals, most notably ringed seals
(Pusa hispida) (Lønø 1970 Smith 1980 Derocher et al. 2002 Thiemann et al.
2008). Bearded seals (Erignathus barbatus) and walruses (Odobenus rosmarus)
are also consumed by bears throughout the Arctic (Lønø 1970 Smith 1980
Calvert and Stirling 1990 Derocher et al. 2002 Thiemann et al. 2008). Other seal
species such as harp (Pagophilus groenlandicus), hooded (Cystophora cristata)
and harbor (Phoca vitulina) seals are preyed upon in areas where they are
available (Lønø 1970 Derocher et al. 2002 Thiemann et al. 2008). In some areas,
polar bears also hunt toothed whales such as white whales (Delphinapterus
leucas) (Smith 1985 Lowry et al. 1987) and narwhals (Monodon monocerus)
(Smith and Sjare 1990). Despite being highly specialized in hunting ice-associated
marine mammals, polar bears are opportunistic feeders. They have been observed
hunting in bird rookeries and cliffs where they take eggs and chicks and also
occasionally live adult birds (Stempniewicz 1993 Drent and Prop 2008 Rockwell
and Gormezano 2009 Smith et al. 2010). Polar bears have also been reported to
chase marine birds in the water (Stempniewicz 2006)

Marianne Iversen, Jon Aars, Tore Haug, Inger G. Alsos, Christian Lydersen, Lutz Bachmann, Kit M. Kovacs (2013) The diet of polar bears (Ursus maritimus) from Svalbard, Norway, inferred from scat analysis Polar Biology Volume 36, Issue 4, pp. 561-571

Here the pdf:
Some of the heaviest known polar bears on record

I'm short, on time, but this sounds awesome!
Hair from the Himalayas matches DNA extracted from 40,000 year old polar bears.

Abominable news: scientists rule out yetis
The yeti, and his shambling hairy cousins the bigfoot, almasty, sasquatch and migyur, may still be out there, high in the snowy peaks of the Himalayas, Rocky Mountains or Urals – but they have escaped a team of scientists who have been testing dozens of samples, all claimed to be genuine chunks of yeti fur.

They have turned out to be hairs from depressingly familiar animals including cows, raccoons, horses, dogs, sheep, a Malayan tapir, a porcupine, and, in the case of one sample from Texas, a human being. And also a blade of grass and a strand of fibreglass.

"Don't give up yet, the yeti may still be out there," Bryan Sykes said reassuringly. The professor of human genetics at Oxford and an expert on ancient DNA, said he launched the project, writing to museums and collectors all over the world, with only a 5% hope of success.

"That would normally be too slim a margin to launch a major study," Sykes said, "but I did think there was just a chance we would uncover something extraordinary."

What he hoped for was less the abominable snowman of legend than evidence for a surviving Neanderthal, which some say could be the origin of yeti stories.

He found neither. However, the team, which publishes its findings in this week's Proceedings of the Royal Society, has found something almost equally extraordinary, in two samples of bear fur from Bhutan and the Indian Himalayas.

Although one is reddish brown and the other golden brown, the bear's closest relative turned out to be a precise match for DNA extracted from fossil remains of a polar bear that lived 40,000 years ago. The samples were quite unlike modern polar bears. This raises the intriguing possibility that descendents of a prehistoric polar bear are at large in the Himalayas.

The sample from Ladakh in India is said to be from an animal shot 40 years ago by an experienced hunter, who said the creature's behaviour was very different from the brown bears he knew well.

He kept the pelt hidden, and, according to Sykes, was very reluctant to hand over samples to the French explorer who brought them back to the west. The other sample came from Bhutan, where yetis – referred to by the scientists as "anomalous primates" – are known as migyur.

"Polar bears have some quite distinct behaviour, including deliberately hunting human prey," Sykes said. "It would be very interesting to go and see if this is a behavioural pattern which has endured in the Himalayan bears."

The paper is the first such study in a peer-reviewed journal. Sykes, who is also publishing a book on yetis this autumn – "I wouldn't have done this as a young man, before I had an established reputation as a scientist," he admitted – said he was struck that science was accused by yeti enthusiasts of rejecting the notion of their existence. "This conflicts with the basic tenet that science neither rejects nor accepts anything without examining the evidence," the team wrote.

Scientists had largely avoided "this often murky field" for more than half a century, Sykes said, since they joined expeditions in the 1950s led by Sir Edmund Hillary and other explorers. Back then, they could not have conducted sophisticated DNA testing.

Samples poured in from collections all over the world, but the only mystery about most was the enduring one of human credulity. Two sent from Russia were claimed to be hairs from an almasty, the Russian version of the bigfoot. They proved to be raccoon and black bear hairs, both natives of North America. The tapir hair came from Sumatra, cow hairs from several places in the US along with the porcupine quill, and a hair from a serow, a goat like creature, from Nepal.

"Absence of evidence is not evidence of absence, and this survey cannot refute the existence of anomalous primates," the authors wrote. There is more work to be done, Sykes said – but the grass and the fibreglass have definitely been eliminated from his inquiries.

Jun 20, 2018 #17 2018-06-20T11:02

Environmental Toxins Enter the Brain Tissue of Polar Bears

July 23, 2013 — Scientists from Denmark and Canada are worried by their new findings showing that several bioaccumulative perfluoroalkyl substances (PFASs) are crossing the blood brain barrier of polar bears from Scoresby Sound, East Greenland.
PerFluoroAlkyl Substances (PFASs) and precursor compounds have been used in a wide variety of commercial and industrial products over the past six decades. Applications include water and oil repellent coatings, e.g. for textiles, paper products, carpets and food packaging, pharmaceuticals and surfactants in cleaning products and fire-fighting foams. PFASs are highly resistant to chemical, thermal and biological degradation.
PFASs and their precursor compounds have shown a dramatic increase and dispersal around the world over the past four decades. An increasing amount of information is becoming available on the toxicity of these compounds. Hence, studies have documented the toxicity of PFASs on wildlife and human health, including carcinogenesis, genotoxicity and epigenetic effects as well as reproductive and developmental toxicities, neurotoxicity, effects on the endocrine system and immunotoxicity.
Bioaccumulative PFASs enter all parts of the brain
Despite the fact that the liver is considered the major repository in the body for most PFASs, some shorter chain compounds from this grouping have previously been reported in the brain of chicken embryos, suggesting that they are able to cross the blood-brain barrier.
Previous studies have shown a dramatic biomagnification of several PFASs, and particularly one known as perfluorooctane sulfonate (PFOS) as well as several compounds of the perfluorinated carboxylate (PFCAs) grouping, in polar bears. PFOS have been shown to be at concentrations in the liver that are 100 fold higher than the ringed seals on which they are predating. In a new study Arctic researchers from Carleton University in Canada and Aarhus University in Denmark have used the polar bear as a sentinel species for humans and other predators in the top of the food chain. The researchers demonstrated accumulation of PFOS and several PFCAs in eight brain regions of polar bears collected from Scoresby Sound, East Greenland. Dr. Robert Letcher, Carleton University, explains:
"We know that fat soluble contaminants are able to cross the brain-blood barrier, but is it quite worrying that the PFOS and PFCAs, which are more associated with proteins in the body, were present in all the brain regions we analyzed."
Professor Rune Dietz, Aarhus University, is also worried about the results: "If PFOS and PFCAs can cross the blood-brain barrier in polar bears, it will also be the case in humans. The brain is one of the most essential parts of the body, where anthropogenic chemicals can have a severe impact. However, we are beginning to see the effect of the efforts to minimize the dispersal of this group of contaminants."
Select environmentally labeled products
The eight carbon chain PFOS and perfluorooctane carboxylate (PFOA) are PFASs have been phased out and are no longer produced in the western world. However, production in China, today the only known production source of PFOS and PFOA, has increased by roughly a factor of 10, since it was phased out in the USA. Unfortunately, no emission inventory is so far available from this region. Furthermore, replacements for PFOS and PFOA are now marketed and produced in e.g. the U.S.A. and China, which generally have perfluorinated carbon chains that are shorter or branched.
Another recent study from Aarhus University documents that PFOS concentrations in Greenlandic polar bears and ringed seals started to decline after 2006. Other wildlife populations closer to the sources in Europe and North America have shown a decline prior to the Greenlandic animals. Rune Dietz comments: "It is promising to see that the PFAS are on the decline. This development should be encouraged by the authorities globally.
In the meantime my best advice to the consumers is to go for environmentally labeled products. But avoiding products is difficult, because PFASs are so widespread in many kind of products and they are rarely declared."
FACTS With fluorine in the tail
Perfluoroalkyl substances (PFASs) constitute a group of compounds where one end of the molecule consists of a carbon chain in which all the hydrogen atoms are replaced by fluorine atoms. This so-called perfluoroalkyl "tail" can be short or long, but the strong C-F bonds make the tail more or less impossible to degrade, compared to the more well known CFC-bonds. The best known PFAS is PFOS with an eight-chained perfluoroalkyl tail.
Journal Reference:
Greaves, A.K., R.J. Letcher, C. Sonne, R. Dietz. Brain region distribution and patterns of bioaccumulative perfluoroalkyl carboxylic and sulfonic acids in highly exposed East Greenland polar bears (Ursus maritimus). Environ. Toxicol. Chem., 2013 DOI: 10.1002/etc.2107

The present study investigated the comparative accumulation of perfluoroalkyl acids (PFAAs) in eight brain regions of polar bears (Ursus maritimus, n=19) collected in 2006 from Scoresby Sound, East Greenland. The PFAAs studied were perfluoroalkyl carboxylates (PFCAs, C6C15 chain lengths) and sulfonates (C4, C6, C8, and C10 chain lengths) as well as selected precursors including perfluorooctane sulfonamide. On a wet-weight basis, bloodbrain barrier transport of PFAAs occurred for all brain regions, although inner regions of the brain closer to incoming blood flow (pons/medulla, thalamus, and hypothalamus) contained consistently higher PFAA concentrations compared to outer brain regions (cerebellum, striatum, and frontal, occipital, and temporal cortices). For pons/medulla, thalamus, and hypothalamus, the most concentrated PFAAs were perfluorooctane sulfonate (PFOS), ranging from 47 to 58ng/g wet weight, and perfluorotridecanoic acid, ranging from 43 to 49ng/g wet weight. However, PFOS and the longer-chain PFCAs (C10C15) were significantly (p0.05) different among brain regions. The burden of the sum of PFCAs, perfluoroalkyl sulfonates, and perfluorooctane sulfonamide in the brain (average mass, 392g) was estimated to be 46 mu g. The present study demonstrates that both PFCAs and perfluoroalkyl sulfonates cross the bloodbrain barrier in polar bears and that wet-weight concentrations are brain regionspecific.

Jun 20, 2018 #18 2018-06-20T11:02

Climate Change: Polar Bears Change to Diet With Higher Contaminant Loads

Sep. 20, 2013 — Over the past 30 years, polar bears have increasingly exchanged ringed seal with harp seal and hooded seal in their diet. This change exposes the polar bear to more contaminants, according to a recent international study.
Researchers expect the climate to become warmer in the future and predict that climate change will have a significant impact on the Arctic. How will a warming Arctic affect the polar bears?
The East Greenlandic population of polar bears resides in an area, where the Arctic sea ice is expected to disappear very late. However, the decline in the ice sheet here occurs at a rate of almost 1% per year, one of the highest rates measured in the entire Arctic region.
How does this affect the prey of the polar bears -- and, in turn, the polar bears' intake of contaminants? An international team of researchers set out to explore this question. The team counted researchers from the Greenland Institute of Natural Resources, Aarhus University (Denmark) and a number of Canadian institutions including: Dalhousie University, Great Lakes Institute for Environmental Research, University of Windsor, Carleton University and the National Water Research Institute.
The researchers studied the fatty acid profiles in the adipose tissue from a unique material of 310 polar bears hunted by East Greenland Inuits from the Scoresbysund area in the years from 1984 to 2011. The composition of fatty acids in the fat tissue of the polar bears namely reflects the profile of fatty acids in their diet.
The results show that the polar bears primarily feed on three species of seals: the high Arctic ringed seal and the two sub-Arctic species harp seal and hooded seal. Moreover, the results showed that the diet of the polar bears had changed over the almost 30 years during which the samples were collected. In this period, the average relative decline in the ringed seal's significance for the polar bears diet was 42%. Similarly, the intake of the sub-Arctic seals increased during the same period. Also, the researchers found that polar bears are generally in better condition now, so at a first glance the polar bears should be happy with this development.
Climate change undermines improvements
There are, however, a couple of problems that might mar the happiness, explains Professor Rune Dietz, Aarhus University:
"The problem is that the sub-Arctic seals that the polar bear has switched to, have a higher content of contaminants because they live closer to the industrialised world and are higher up in the food chain. Therefore, climate change undermines the improvements that you would otherwise have obtained owing to international regulations in the use of environmental use of persistent organic pollutants (POPs). We can see that the content of the POPs after year 2000 decreases slower in the polar bear than in, the ringed seal."
In the long term, the polar bear may very well lose access to the sub-Arctic seals as these depend on packed ice where they give birth to their cubs and are exposed to sunlight allowing them to form vital vitamin D.
Journal References:
Melissa A. McKinney, Sara J. Iverson, Aaron T. Fisk, Christian Sonne, Frank F. Rigét, Robert J. Letcher, Michael T. Arts, Erik W. Born, Aqqalu Rosing-Asvid, Rune Dietz. Global change effects on the long-term feeding ecology and contaminant exposures of East Greenland polar bears. Global Change Biology, 2013 19 (8): 2360 DOI: 10.1111/gcb.12241
Rune Dietz, Frank F. Rigét, Christian Sonne, Erik W. Born, Thea Bechshøft, Melissa A. McKinney, Robert J. Letcher. Three decades (1983–2010) of contaminant trends in East Greenland polar bears (Ursus maritimus). Part 1: Legacy organochlorine contaminants. Environment International, 2013 59: 485 DOI: 10.1016/j.envint.2012.09.004
Rune Dietz, Frank F. Rigét, Christian Sonne, Erik W. Born, Thea Bechshøft, Melissa A. McKinney, Robert J. Drimmie, Derek C.G. Muir, Robert J. Letcher. Three decades (1983–2010) of contaminant trends in East Greenland polar bears (Ursus maritimus). Part 2: Brominated flame retardants. Environment International, 2013 59: 494 DOI: 10.1016/j.envint.2012.09.008

Jun 20, 2018 #19 2018-06-20T11:03

Polar Bear Diet Changes as Sea Ice Melts

Jan. 22, 2014 — A series of papers recently published by scientists at the American Museum of Natural History suggests that polar bears in the warming Arctic are turning to alternate food sources. As Arctic sea ice melts earlier and freezes later each year, polar bears have a limited amount of time to hunt their historically preferred prey -- ringed seal pups -- and must spend more time on land. The new research indicates that at least some polar bears in the western Hudson Bay population are using flexible foraging strategies while on land, such as prey-switching and eating a mixed diet of plants and animals, as they survive in their rapidly changing environment.
"There is little doubt that polar bears are very susceptible as global climate change continues to drastically alter the landscape of the northern polar regions," said Robert Rockwell, a research associate in the Museum's Department of Ornithology. "But we're finding that they might be more resilient than is commonly thought."
Polar bears are listed as a threatened species under the United States Endangered Species Act and are classified as "vulnerable" with declining populations on the International Union for Conservation of Nature and Natural Resources' Red List. Climate warming is reducing the availability of their ice habitat, especially in the spring when polar bears gain most of their annual fat reserves by consuming seal pups before coming ashore for the summer. The new work, led by Rockwell and Linda Gormezano, a postdoctoral researcher in the Museum's Division of Vertebrate Zoology, examines how polar bears might compensate for energy deficits from decreasing seal-hunting opportunities.
In the first paper, published in spring 2013 in the journal Polar Ecology, the researchers provide, for the first time, data and video of polar bears pursuing, catching, and eating adult and juvenile lesser snow geese during mid-to-late summer, when the geese are replacing their primary flight feathers.
In the second paper, published in summer 2013 in the journal Ecology and Evolution, researchers used polar bear scat to show that the diet of at least some of the bears has shifted from what it was 40 years ago, before climate change was affecting the Hudson Bay lowlands. Today's polar bears are preying more on caribou as well as on snow geese and their eggs.
In the final paper in the series, published in December 2013 in the journal BMC Ecology, the researchers show that polar bears are, with a few exceptions, consuming a mixed diet of plants and animals. The predominance of local vegetation in collected scat suggests little movement among habitat types between feeding sessions, indicating that the polar bears are keeping energy expenditure down.
Taken together, the research indicates that during the ice-free period, polar bears are exhibiting flexible foraging behavior. This behavior likely derives from a shared genetic heritage with brown bears, from which polar bears separated about 600,000 years ago.
"For polar bear populations to persist, changes in their foraging will need to keep pace with climate-induced reduction of sea ice from which the bears typically hunt seals," Gormezano said. "Although different evolutionary pathways could enable such persistence, the ability to respond flexibly to environmental change, without requiring selective alterations to underlying genetic architecture, may be the most realistic alternative in light of the fast pace at which environmental changes are occurring. Our results suggest that some polar bears may possess this flexibility and thus may be able to cope with rapidly changing access to their historic food supply."
Funding for this work was provided by the Hudson Bay Project the American Museum of Natural History Churchill Northern Studies Centre City University of New York and Manitoba Conservation.

Journal References:
D. T. Iles, S. L. Peterson, L. J. Gormezano, D. N. Koons, R. F. Rockwell. Terrestrial predation by polar bears: not just a wild goose chase. Polar Biology, 2013 36 (9): 1373 DOI: 10.1007/s00300-013-1341-5

Behavioral predictions based on optimal foraging models that assume an energy-maximizing strategy have been challenged on both theoretical and empirical grounds. Although polar bears (Ursus maritimus) are specialist predators of seal pups on the Arctic ice pack, the use of terrestrial food sources during the ice-free period has received increased attention in recent years in light of climate predictions. Across a 10-day period of observation, we documented between four and six individual polar bears successfully capture at least nine flightless lesser snow geese (Chen caerulescens caerulescens) and engage in at least eight high-speed pursuits of geese. The observed predatory behaviors of polar bears do not support predictions made by energy-optimizing foraging models and suggest that polar bears may frequently engage in energy inefficient pursuits of terrestrial prey. Further study of the nutritional needs and foraging behaviors of polar bears during the ice-free period is warranted, given that polar bears are predicted to spend more time on land as climate change advances.

Linda J. Gormezano, Robert F. Rockwell. What to eat now? Shifts in polar bear diet during the ice-free season in western Hudson Bay. Ecology and Evolution, 2013 DOI: 10.1002/ece3.740

Under current climate trends, spring ice breakup in Hudson Bay is advancing rapidly, leaving polar bears (Ursus maritimus) less time to hunt seals during the spring when they accumulate the majority of their annual fat reserves. For this reason, foods that polar bears consume during the ice-free season may become increasingly important in alleviating nutritional stress from lost seal hunting opportunities. Defining how the terrestrial diet might have changed since the onset of rapid climate change is an important step in understanding how polar bears may be reacting to climate change. We characterized the current terrestrial diet of polar bears in western Hudson Bay by evaluating the contents of passively sampled scat and comparing it to a similar study conducted 40 years ago. While the two terrestrial diets broadly overlap, polar bears currently appear to be exploiting increasingly abundant resources such as caribou (Rangifer tarandus) and snow geese (Chen caerulescens caerulescens) and newly available resources such as eggs. This opportunistic shift is similar to the diet mixing strategy common among other Arctic predators and bear species. We discuss whether the observed diet shift is solely a response to a nutritional stress or is an expression of plastic foraging behavior.

Linda J Gormezano, Robert F Rockwell. Dietary composition and spatial patterns of polar bear foraging on land in western Hudson Bay. BMC Ecology, 2013 13 (1): 51 DOI: 10.1186/1472-6785-13-51

Flexible foraging strategies, such as prey switching, omnivory and food mixing, are key to surviving in a labile and changing environment. Polar bears (Ursus maritimus) in western Hudson Bay are versatile predators that use all of these strategies as they seasonally exploit resources across trophic levels. Climate warming is reducing availability of their ice habitat, especially in spring when polar bears gain most of their annual fat reserves by consuming seal pups before coming ashore in summer. How polar bears combine these flexible foraging strategies to obtain and utilize terrestrial food will become increasingly important in compensating for energy deficits from lost seal hunting opportunities. We evaluated patterns in the composition of foods in scat to characterize the foraging behaviors that underpin the diet mixing and omnivory observed in polar bears on land in western Hudson Bay. Specifically, we measured diet richness, proportions of plant and animal foods, patterns in co-occurrence of foods, spatial composition and an index of temporal composition.
Scats contained between 1 and 6 foods, with an average of 2.11 (SE = 0.04). Most scats (84.9%) contained at least one type of plant, but animals (35.4% of scats) and both plants and animals occurring together (34.4% of scats) were also common. Certain foods, such as Lyme grass seed heads (Leymus arenarius), berries and marine algae, were consumed in relatively higher proportions, sometimes to the exclusion of others, both where and when they occurred most abundantly. The predominance of localized vegetation in scats suggests little movement among habitat types between feeding sessions. Unlike the case for plants, no spatial patterns were found for animal remains, likely due the animals' more vagile and ubiquitous distribution.
Our results suggest that polar bears are foraging opportunistically in a manner consistent with maximizing intake while minimizing energy expenditure associated with movement. The frequent mixing of plant-based carbohydrate and animal-based protein could suggest use of a strategy that other Ursids employ to maximize weight gain. Further, consuming high rates of certain vegetation and land-based animals that may yield immediate energetic gains could, instead, provide other benefits such as fulfilling vitamin/mineral requirements, diluting toxins and assessing new foods for potential switching.


Camouflage, also called cryptic coloration, is a defense mechanism or tactic that organisms use to disguise their appearance, usually to blend in with their surroundings. Organisms use camouflage to mask their location, identity, and movement.

Biology, Ecology, Geography

Camouflage, also called cryptic coloration, is a defense or tactic that organisms use to disguise their appearance, usually to blend in with their surroundings. Organisms use camouflage to mask their location, identity, and movement. This allows prey to avoid predators, and for predators to sneak up on prey.

A species&rsquo camouflage depends on several factors. The physical characteristics of the organism are important. Animals with fur rely on different camouflage tactics than those with feathers or scales, for instance. Feathers and scales can be shed and changed fairly regularly and quickly. Fur, on the other hand, can take weeks or even months to grow in. Animals with fur are more often camouflaged by season. The arctic fox, for example, has a white coat in the winter, while its summer coat is brown.

The behavior of a species is also important. Animals that live in groups differ from those that are solitary. The stripes on a zebra, for instance, make it stand out. However, zebras are social animals, meaning they live and migrate in large groups called herds. When clustered together, it is nearly impossible to tell one zebra from another, making it difficult for predators such as lions to stalk an individual animal.

A species&rsquo camouflage is also influenced by the behavior or characteristics of its predators. If the predator is color-blind, for example, the prey species will not need to match the color of its surroundings. Lions, the main predator of zebras, are color-blind. Zebras&rsquo black-and-white camouflage does not need to blend in to their habitat, the golden savanna of central Africa.

Camouflage Tactics

Environmental and behavioral factors cause species to employ a wide variety of camouflage tactics. Some of these tactics, such as background matching and disruptive coloration, are forms of mimicry. Mimicry is when one organism looks or acts like an object or another organism.

Background matching is perhaps the most common camouflage tactic. In background matching, a species conceals itself by resembling its surroundings in coloration, form, or movement. In its simplest form, animals such as deer and squirrels resemble the &ldquoearth tones&rdquo of their surroundings. Fish such as flounder almost exactly match their speckled seafloor habitats.

More complex forms of background matching include the camouflage of the walking stick and walking leaf. These two insects, both native to southeast Asia, look and act like their namesakes. Patterns on the edge of the walking leaf&rsquos body resemble bite marks left by caterpillars in leaves. The insect even sways from side to side as it walks, to better mimic the swaying of a leaf in the breeze.

Another camouflage tactic is disruptive coloration. In disruptive coloration, the identity and location of a species may be disguised through a coloration pattern. This form of visual disruption causes predators to misidentify what they are looking at. Many butterflies have large, circular patterns on the upper part of their wings. These patterns, called eyespots, resemble the eyes of animals much larger than the butterfly, such as owls. Eyespots may confuse predators such as birds and misdirect them from the soft, vulnerable part of the butterfly&rsquos body.

Other species use coloration tactics that highlight rather than hide their identity. This type of camouflage is called warning coloration or aposematism. Warning coloration makes predators aware of the organism&rsquos toxic or dangerous characteristics. Species that demonstrate warning coloration include the larva and adult stages of the monarch butterfly. The monarch caterpillar is brightly striped with yellow, black, and white. The monarch butterfly is patterned with orange, black, and white. Monarchs eat milkweed, which is a poison to many birds. Monarchs retain the poison in their bodies. The milkweed toxin is not deadly, but the bird will vomit. The bright coloring warns predator birds that an upset stomach is probably not worth a monarch meal.

Another animal that uses aposematism is the deadly coral snake, whose brightly colored rings alert other species to its toxic venom. The coral snake&rsquos warning coloration is so well known in the animal kingdom that other, non-threatening species mimic it in order to camouflage their true identities. The harmless scarlet king snake has the same black, yellow, and red striped pattern as the coral snake. The scarlet king snake is camouflaged as a coral snake.

Countershading is a form of camouflage in which the top of an animal&rsquos body is darker in color, while its underside is lighter. Sharks use countershading. When seen from above, they blend in with the darker ocean water below. This makes it difficult for fishermen&mdashand swimmers&mdashto see them. When seen from below, they blend in with lighter surface water. This helps them hunt because prey species below may not see a shark until it&rsquos too late.

Countershading also helps because it changes the way shadows are created. Sunlight illuminates the top of an animal&rsquos body, casting its belly in shadow. When an animal is all one color, it will create a uniform shadow that makes the animal&rsquos shape easier to see. In countershading, however, the animal is darker where the sun would normally illuminate it, and lighter where it would normally be in shadow. This distorts the shadow and makes it harder for predators to see the animal&rsquos true shape.

Creating Camouflage

Animal species are able to camouflage themselves through two primary mechanisms: pigments and physical structures.

Some species have natural, microscopic pigments, known as biochromes, which absorb certain wavelengths of light and reflect others. Species with biochromes actually appear to change colors. Many species of octopus have a variety of biochromes that allow them to change the color, pattern, and opacity of their skin.

Other species have microscopic physical structures that act like prisms, reflecting and scattering light to produce a color that is different from their skin. The polar bear, for instance, has black skin. Its translucent fur reflects the sunlight and snow of its habitat, making the bear appear white.

Camouflage can change with the environment. Many animals, such as the arctic fox, change their camouflage with the seasons. Octopuses camouflage themselves in response to a threat. Other species, such as nudibranchs&mdashbrightly colored, soft-bodied ocean &ldquoslugs&rdquo&mdashcan change their skin coloration by changing their diet.

Chameleons change colors in order to communicate. When a chameleon is threatened, it does not change color to blend in to its surroundings. It changes color to warn other chameleons that there is danger nearby.

Some forms of camouflage are not based on coloration. Some species attach or attract natural materials to their bodies in order to hide from prey and predators. Many varieties of desert spiders, for instance, live in burrows in the sandy ground. They attach sand to the upper part of their bodies in order to blend in with their habitat.

Other animals demonstrate olfactory camouflage, hiding from prey by &ldquocovering up&rdquo their smell or masking themselves in another species&rsquo smell. The California ground squirrel, for instance, chews up and spits out rattlesnake skin, then applies the paste to its tail. The ground squirrel smells somewhat like its main predator. The rattlesnake, which senses by smell and body heat, is confused and hesitant about attacking another venomous snake.

Photograph by Steve Irvine, MyShot

Ghillie Suits
Ghillie suits are a type of camouflage used by the military and hunters to blend in to thick vegetation. In addition to patterns of contrasting green or khaki, ghillie suits feature elements of foliage from the area: twigs, leaves, and branches.

In Australia, ghillie suits are nicknamed "yowies," for their resemblance to the Yowie, a mythical creature similar to Bigfoot.

Khaki Camouflage
Militaries did not use camouflage until the 17th and 18th centuries. Before then, military uniforms were brightly colored, in order to intimidate the enemy.

In the 1850s, the British Army suffered massive casualties in India. (Indians were fighting for their independence.) British leaders dyed their bright white uniforms a dull, sandy tan to blend in with the desert surroundings. They called these newly colored uniforms khakis, a Hindu word for "dust."

Razzle Dazzle
Razzle Dazzle, or dazzle camouflage, was a tactic used by Allied forces during World War I and World War II. Large ships, such as aircraft carriers, were painted with bold, geometric patterns. Razzle Dazzle did not camouflage the so-called "dazzle ships," but made it difficult for opposing forces to judge the size and type of the vessel.

Sneaky Snakes
The scarlet king snake is harmless, but its black, yellow, and red stripes mimic the stripes of the deadly coral snake. The only real difference between the two patterns is the order of the colors. The coral snakes pattern is red-yellow-black. The scarlet king snakes pattern is red-black-yellow.

A rhyme makes the distinction easy to remember.
Red on yellow kills a fellow,
Red on black wont hurt Jack.

Dressing for the Part
The dresser crab gets its name for a reason: The animal picks up pieces of coral and sponge with its claws and places them on the Velcro-like hairs that cover its body. When a predator, such as a blowfish, passes by, the dresser crab freezes, blending into the seafloor. The dresser crab adapts to its environment so well that even when placed in a fish tank full of human objects, such as lace and pearl necklaces, the creature will get "dressed up" for the occasion, appearing to be just another trinket at the bottom of the tank.