Information

How can birds keep their eyes moist during flight?

How can birds keep their eyes moist during flight?


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Mammals have an upper lid and small mass of tissue in the upper corner known as nictitating membrane. This helps keep the eyes clean; birds can moisten their eyes in flight using this membrane without blinking. How does this work?


Because the nictitating membrane secretes a fluid that is resistant to evaporation. Therefore, birds need not blink their eyes during flight.


Learn About Birds

Birds have special ways of surviving. Their bodies are a major one. Special lightweight bones help them fly and feathers help protect them from bad weather.

Bones. Birds have very lightweight bones. Their bones are also very strong, so that they do not break under the pressures of flight. The bones in bird legs and wings are hollow, providing space for tiny air sacs. Flightless birds, however, have solid bones.

Lungs. Most of the air that enters a bird is not used for breathing! It is used to cool down the bird’s insides, which can easily become heated during flight. Birds have lungs and also a system of air sacs. The air sacs make the bird lighter, helping it float in air or water.

Heart. Like people, birds have a four-chambered heart. It pumps blood very quickly through a bird’s body to cope with the hard work of flying. The veins and arteries that supply blood to the wing muscles are especially large, since the body parts that are used for flying work the hardest.

Feathers. Instead of skin or fur, birds are covered with feathers. Feathers provide a waterproof layer for birds and act as an insulator so they can maintain a high body temperature. Birds usually need to maintain a body temperature of 110 degrees Fahrenheit! Do you know what temperature our bodies maintain? (Answer: 98.6 degrees Fahrenheit.)

Feathers have their own unique anatomy. If you have a feather, you might want to observe the different parts. Use a magnifying glass to see the tiniest parts. The hard, stem-like section of the feather is called the rachis. The “branches” of the feather are called vanes. Each vane is made up of more tiny parts. The stem of the vane is called a barb. Branching from the barb are tiny barbules, each with little hooks on them. The hooks work like Velcro, to connect the vanes of the feather and hold them together. This is why it is so difficult to separate the vanes of a feather from each other. Learn more about feathers here.

Eyes. Have you ever noticed how birds have to turn their heads to look at an object? That is because their eyes aren’t able to move very much. However, birds are able to see a greater range of the color spectrum than people can. They also have the ability to focus on two different objects out of each eye! Each eye has two foveae, the part of the retina which “sees” most clearly.

Bills. Bills are uniquely tailored for the different eating functions required by each species of bird. They don’t have teeth, so their beaks are important! Birds with short beaks, such as sparrows and finches, eat small seeds. Cardinals and grosbeaks have slightly larger, stubby bills to hold the large seeds that they eat. Meat-eating birds, like hawks and eagles, have hooked bills to tear their prey. Woodpeckers have long, narrow bills for extracting insects from dead wood. Toucans have large, hollow bills for collecting fruit and cracking it apart. Most sea birds have long bills, to capture and hold fish.

Your children might enjoy guessing what different birds eat. Collect pictures of different kinds of birds from nature magazines or books. Hypothesize with your children about what kind of food each bird eats, based on its bill shape and size. To check your hypotheses, use a bird guide or an encyclopedia and read about what each bird eats. Discuss how close your guesses were to the answers. Do you have a general idea now of how bill shape and size fit each bird?

How Birds Fly

Most birds use flying as their primary mode of transportation. However, some birds can’t fly at all! (You’ll learn more about them below.) A bird’s lightweight bones and specially designed wings make flying easy. They also have special strong muscles to support their wings during flight and to keep them moving, even when they have to fly over very long distances. A bird’s wing is curved from the front to the back, the same way an airplane’s wings are. The special shape allows the air to push the bird along as it flaps its wings. There is more pressure from the air pushing up (from the bottom) on the wing than there is pushing down (from the top of the wing). This is called lift. It helps a bird take-off and stay in the air.

Besides flapping, there are other techniques birds use to fly. They can stretch out their wings and glide slowly down towards the ground without flapping. Ducks often glide down to land in water.

A similar way of flying is called soaring. Instead of going downwards, though, a bird can soar when it stretches out its wings over warm air. Since warm air rises, it pushes the bird upwards. Hawks and eagles often soar.

Some birds can fly sort of the way helicopters do — by hovering! In order to hover, a bird must flap its wings very very quickly hummingbirds flap their wings over 50 times per second! This quick movement allows them to fly backwards as well as forwards. They can also fly up or down, and side to side, much like a helicopter.

Flightless Birds

All birds have wings, but not all birds can fly! Some birds can’t fly at all and are called flightless birds. Their wings aren’t designed for flying. Penguins, for example, use their short wings like flippers to help them swim. In fact, penguins are excellent swimmers — it’s not unusual for one to swim a total of over 100 miles just to find food. Flightless birds usually have much smaller and shorter wings than birds that fly. Their feathers are also smaller and are symmetrically shaped (each half of the feather looks the same – like a butterfly’s wings). Birds that fly have asymmetrical feathers (one side of the feather is usually larger and more rounded). Birds that don’t fly also usually have more feathers covering all of their bodies. Kiwi birds, Emu, Ostriches, and Penguins are a few kinds of flightless birds. Some flightless birds are now extinct, such as the Dodo bird.


First evidence of sleep in flight

For the first time, researchers have discovered that birds can sleep in flight. Together with an international team of colleagues, Niels Rattenborg from the Max Planck Institute for Ornithology in Seewiesen measured the brain activity of frigatebirds and found that they sleep in flight with either one cerebral hemisphere at a time or both hemispheres simultaneously. Despite being able to engage in all types of sleep in flight, the birds slept less than an hour a day, a mere fraction of the time spent sleeping on land. How frigatebirds are able to perform adaptively on such little sleep remains a mystery.

It is known that some swifts, songbirds, sandpipers, and seabirds fly non-stop for several days, weeks, or months as they traverse the globe. Given the adverse effect sleep loss has on performance, it is commonly assumed that these birds must fulfill their daily need for sleep on the wing.

Half-awake or fully awake in flight?

How might a bird sleep in flight without colliding with obstacles or falling from the sky? One solution would be to only switch off half of the brain at a time, as Rattenborg showed in mallard ducks sleeping in a dangerous situation on land. When sleeping at the edge of a group, mallards keep one cerebral hemisphere awake and the corresponding eye open and directed away from the other birds, toward a potential threat. Based on these findings and the fact that dolphins can swim while sleeping unihemispherically, it is commonly assumed that birds also rely on this sort of autopilot to navigate and maintain aerodynamic control during flight.

However, it is also possible that birds evolved a way to cheat on sleep. The sleep researcher's and colleagues' recent discovery that male pectoral sandpipers competing for females can perform adaptively for several weeks despite sleeping very little raised the possibility that birds simply forgo sleep altogether in flight. Consequently, evidence of continuous flight is not by default evidence of sleep in flight: Without directly measuring a bird's brain state, previous claims that birds sleep in flight remain mere speculation.

Flight data recorder catches birds napping on the wing

To actually determine whether and how birds sleep in flight, the researchers needed to record the changes in brain activity and behavior that distinguish wakefulness from the two types of sleep found in birds: slow wave sleep (SWS) and rapid eye movement (REM) sleep. Niels Rattenborg teamed up with Alexei Vyssotski (University of Zurich and Swiss Federal Institute of Technology, ETH) who developed a small device to measure electroencephalographic changes in brain activity and head movements in flying birds.

In collaboration with the Galápagos National Park and Sebastian Cruz, an Ecuadorian seabird biologist, the team focused on great frigatebirds nesting on the Galápagos Island. Frigatebirds are large seabirds that spend weeks flying non-stop over the ocean in search of flying fish and squid driven to the surface by predatory fish and cetaceans. The researchers temporarily attached the small "flight data recorder" to the head of nesting female frigatebirds. The birds then carried the recorder during non-stop foraging flights lasting up to ten days and 3000 kilometers. During this time, the recorder registered the EEG activity of both brain hemispheres and movements of the head, while a GPS device on the birds' back tracked their position and altitude. After the birds were back on land and had had some time to recover, they were re-caught and the equipment was removed. Bryson Voirin, a post-doc and co-first author on the paper with Rattenborg observed that, "Like many other animals in the Galápagos Islands, the frigatebirds were remarkably calm and would even sleep as I approached to catch them for the second time."

The flight data recorder revealed that frigatebirds sleep in both expected and unexpected ways during flight. During the day the birds stayed awake actively searching for foraging opportunities. As the sun set, the awake EEG pattern switched to a SWS pattern for periods lasting up to several minutes while the birds were soaring. Surprisingly, SWS could occur in one hemisphere at a time or both hemispheres together. The presence of such bihemispheric sleep indicates that unihemispheric sleep is not required to maintain aerodynamic control. Nonetheless, when compared to sleep on land, SWS was more often unihemispheric in flight. By carefully examining the movements of the frigatebirds, the researchers discovered clues to why they sleep unihemispherically in flight. When the birds circled on rising air currents the hemisphere connected to the eye facing the direction of the turn was typically awake while the other was asleep, suggesting that the birds were watching where they were going. "The frigatebirds may be keeping an eye out for other birds to prevent collisions much like ducks keep an eye out for predators", says Rattenborg.

In addition to engaging in both types of SWS in flight, on rare occasions, bouts of SWS were interrupted by brief episodes of REM sleep. Although this finding may seem remarkable to scientists who study sleep in mammals, based on Rattenborg's experience with birds, he was not that surprised. In contrast to mammals, wherein episodes of REM sleep are long and accompanied by a complete loss of muscle tone, REM sleep episodes only last several seconds in birds. In addition, although a reduction in muscle tone can cause the head to drop during avian REM sleep, birds are able to stand (even on one leg) during this state. Similarly, when frigatebirds entered REM sleep their head dropped momentarily, but their flight pattern remained unchanged.

Ecological demands require full attention 24/7 at sea

Perhaps the greatest surprise was that despite being able to engage in all types of sleep on the wing, on average frigatebirds slept only 42 minutes per day. In contrast, when back on land they slept for over twelve hours per day. In addition, episodes of sleep were longer and deeper on land. Collectively, this suggests that frigatebirds are actually sleep deprived in flight. "Why they sleep so little in flight, even at night when they rarely forage, remains unclear", says Rattenborg. As previous studies have shown that frigatebirds follow ocean eddies predictive of good foraging conditions throughout the day and night, perhaps this is what they are up to. Interestingly, the low amount of sleep in flight suggests that this task requires more attention than that afforded by sleeping with one half of the brain at a time. As such, frigatebirds face ecological demands for full attention 24/7 while at sea.

In the long term, Rattenborg hopes to determine how frigatebirds are able to sustain adaptive performance on such little sleep. People will fall asleep driving a car after losing just a few hours of sleep, even when fully aware of the dangers and struggling to keep themselves awake. "Why we, and many other animals, suffer dramatically from sleep loss whereas some birds are able to perform adaptively on far less sleep remains a mystery", notes Rattenborg. Reconciling the findings from frigatebirds with the wealth of evidence underscoring the importance of sleep in other animals may provide new perspectives on our understanding of sleep and the consequences of its loss.

Original paper:

Niels C. Rattenborg, Bryson Voirin, Sebastian M. Cruz, Ryan Tisdale, Giacomo Dell'Omo, Hans-Peter Lipp, Martin Wikelski, Alexei L. Vyssotski

Evidence that birds sleep in mid-flight.

Nature Communications 2016, 7:12468 (doi: 10.1038/ncomms12468 open access)

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


Falcons have natural 'eye makeup' to improve hunting ability

Dark 'eyeliner' feathers of peregrine falcons act as sun shields to improve the birds' hunting ability, a new scientific study suggests.

Scientists have long speculated that falcons' eye markings improve their ability to target fast-moving prey, like pigeons and doves, in bright sunlight. Now research suggests these markings have evolved according to the climate the sunnier the bird's habitat, the larger and darker are the tell-tale dark 'sun-shade' feathers.

The distinctive dark stripes directly beneath the peregrine falcon's eyes, called the malar stripe or 'moustache', likely reduce sunlight glare and confer a competitive advantage during high-speed chases. It's an evolutionary trait mimicked by some top athletes who smear dark makeup below their eyes to help them spot fast-moving balls in competitive sports.

Until now, there had been no scientific study linking solar radiation levels to the dark 'eyeliner' plumage, which is common to many other falcon species.

The study, published in the journal Biology Letters was conducted by researchers from the University of Cape Town (UCT) and the University of Witwatersrand, South Africa.

The scientists used photos of peregrine falcons from around the world posted on the web by bird watchers and scored the size of the malar stripe for each bird. They then explored how these malar stripes varied in relation to aspects of the local climate, such as temperature, rainfall, and strength of sunlight.

The study involved comparing malar stripe characteristics, including width and prominence, of individual peregrine falcons, by using over two thousand peregrine photographs stored in online citizen science libraries. Researchers examined samples from 94 different regions or countries. Results showed that peregrine falcon malar stripes were larger and darker in regions of the world where sunlight is stronger.

"The solar glare hypothesis has become ingrained in popular literature, but has never been tested empirically before," said Michelle Vrettos, an MSc student from UCT who carried out the research. Vrettos added: "Our results suggest that the function of the malar stripe in peregrines is best explained by this solar glare hypothesis."

Associate Professor Arjun Amar from the UCT FitzPatrick Institute, who supervised the research, said: "The peregrine falcon represents the ideal species to explore this long-standing hypothesis, because it has one of the most widespread distributions of all bird species, being present on every continent except Antarctica -- it is therefore exposed to some of the brightest and some of the dullest areas around the globe."

Amar added: "We are grateful to all the photographers around the world that have deposited their photos onto websites. Without their efforts this research would not have been possible."


For Migratory Birds, Navigation is All in the Eyes

As the weather gets colder and food more scarce, all sorts of birds will gather the flock and head South for winter. While fall migration for some species starts as soon as late June, the best time to spot avian migrants is near the end of summer and the beginning of fall, with a few stragglers taking off as late as December.

Some birds fly by night, and others during the day some fly one way with no stopovers, while others like to take daily breaks to relax and refuel. Each species of bird has its own specific migration behavior, often based on its unique needs and flight abilities.

Red knots, for instance, will travel from their breeding grounds in the Arctic all the way down to the Tierra del Fuego archipelago at the southern tip of South America — one of the most distant migrations of any animal — while landing in key staging areas along the way. American white pelicans, on the other hand, fly much shorter distances, often during the day, and some don't even migrate at all.

Though birds' ability to navigate earth's magnetosphere has long been a mystery, a new branch of science called “quantum biology” may have finally explained the phenomenon.

While quantum physics and biology may appear incompatible, pioneering scientists now believe that birds are able to visually map earth's magnetism through a widely accepted, but highly perplexing natural mechanism called “quantum entanglement.”

It's all very confusing, even to the most well-educated scientists, but it seems that earth's magnetic field provides migrating birds with an evolutionary advantage by stimulating light-sensitive subatomic particles in the birds' eyes.

Our Featured Programs

See how we’re making a difference for People, Pets, and the Planet and how you can get involved!

Besides magnetic navigation, birds also rely heavily on favorable weather for their migration. Thankfully, Cornell's Lab of Ornithology provides a weekly forecast, arranged by region, that predicts which species will be where and when. It's a pretty useful tool if you're looking to watch some birds this season.

If you're new to bird watching. please be aware that there is a code of ethics for birding. In brief, you'll want to pay respect to the birds (use only pre-existing paths, minimize noise and disturbance, keep your distance), be mindful of others (stay off private property or ask permission to be there, maintain good standing with birders and non-birders alike, make safety a priority), be a steward for the environment, and do your best to respectfully help others follow ethical birding behavior.

For those interested in birds who don't go birding for fear of disturbing them, you can do something even better. Please consider donating toward protecting vital wetland habitats — areas where many birds stopover during some of the most distant migrations.


Extreme blennies are surprisingly ordinary

Extreme environments are often a breeding ground for animals with extreme adaptations. Arctic marine mammals have extraordinary amounts of blubber to keep them warm and sated in their icy landscapes, like the delightfully rotund walrus. The endless expanse of the open ocean has led albatrosses to evolve incredibly long wings to help them soar hundreds to thousands of miles at time before reaching land. The dense, dark underground environment has shaped a group of worm-like, wedge-headed, legless amphibians called caecilians to rein over Subterranea.

One of the most extreme environments on the planet is the intertidal zone, which is covered by water during part of the day and air the rest of the day. In this environment, many organisms have adapted to the rapidly fluctuating temperatures, oxygen levels, salinity, and exposure, from barnacles that are cemented to rocks to fish that can move overland between tide pools. These pools also contain many different species of combtooth blennies, a highly diverse group of mostly small, cryptic fishes. Do intertidal blennies also have extreme adaptations to survive in tide pools compared to their subtidal brethren?

Alticus combtooth blennies are the most extreme of blennies, living beyond the intertidal zone in the splash zone. Splashing waves keep them moist as they graze upon algae. Photo by G. Cooke.

A group of scientists led by Joshua Egan of Western Michigan University sought to answer this question in their recent IOB publication by comparing dozens of combtooth blenny species. Egan and colleagues used previously published observations on habitat to categorize blennies as either intertidal, subtidal, freshwater, or in the splash zone of shores and then mapped these habitat preferences onto a phylogeny, which is essentially a combtooth blenny family tree. Using this data, Egan and colleagues found that intertidal lifestyles evolved multiple times in blennies. They were also able to infer that combtooth blennies were lured to the beaches from deeper water at least four times while at least seven intertidal lineages transitioned to deeper water.

Egan and colleagues also took photos of blennies from museum collections and to compare body shape. To do so, they marked 16 points along their bodies that help describe the shapes of the fish. Next, they compared body shape between species to create a morphospace, which can be thought of as a map that shows how wide of a shape range these blennies occupy, and separated the results by habitat type.

Blennies come in all shapes and colors, from short and stout (top left) to long and skinny (top right). Some have pointy snouts (bottom left) and others have square faces (bottom right). Image modified from Egan et al. (2021).

To much surprise, Egan and colleagues did not see much of a difference between the body shapes of intertidal and subtidal sculpins. In fact, all the intertidal blenny shapes were encompassed within the much larger subtidal shape range. However, while it does not seem like intertidal blennies have any special body shapes that help them survive between the tides, it may mean that only a limited range of combtooth blenny body shapes are well-suited for intertidal life. Meanwhile, subtidal blennies live in a wider variety of habitats, from seagrass flats to coral reefs to oyster beds, where they can adapt to different prey sources and fill a wider variety of niches than intertidal species. Without being limited to and constrained in tide pools, subtidal blennies were able to branch out and develop a wide range of body shapes that help them squeeze into long, narrow invertebrate burrows, feed on coral polyps, and mimic cleaner fish to steal chunks from the bodies from dissatisfied clients.


When eagles choose a partner, it’s ‘Till’ death do us part.‘ As mentioned above, they are a monogamous species. However, if their partner dies early or does not return to the nest for a year or so, it would generally seek a new partner.

When an eagle needs to hunt and eat in mountainous terrains and spot larger prey, it will use its strong talons to grab them and throw them off the high cliff. After they drop dead from free-fall, the eagle will devour its meal.


Footnotes

Electronic supplementary material is available online at https://doi.org/10.6084/m9.figshare.c.5228317.

References

Lin H-T, Ros IG, Biewener AA

. 2014 Through the eyes of a bird: modelling visually guided obstacle flight . J. R. Soc. Interface 11, 20140239. (doi:10.1098/rsif.2014.0239) Link, ISI, Google Scholar

Kress D, van Bokhorst E, Lentink D

. 2015 How lovebirds maneuver rapidly using super-fast head saccades and image feature stabilization . PLoS ONE 10, e0129287. (doi:10.1371/journal.pone.0129287) Crossref, PubMed, ISI, Google Scholar

2015 Pigeons trade efficiency for stability in response to level of challenge during confined flight . Proc. Natl Acad. Sci. USA 112, 3392-3396. (doi:10.1073/pnas.1407298112) Crossref, PubMed, ISI, Google Scholar

. 2015 Eye movements of vertebrates and their relation to eye form and function . J. Comp. Physiol. A 201, 195-214. (doi:10.1007/s00359-014-0964-5) Crossref, ISI, Google Scholar

Yorzinski JL, Patricelli GL, Platt ML, Land MF

. 2015 Eye and head movements shape gaze shifts in Indian peafowl . J. Exp. Biol. 218, 3771-3776. (doi:10.1242/jeb.129544) Crossref, PubMed, ISI, Google Scholar

. 2000 The deep fovea, sideways vision and spiral flight paths in raptors . J. Exp. Biol. 203, 3745-3754. PubMed, ISI, Google Scholar

2014 Falcons pursue prey using visual motion cues: new perspectives from animal-borne cameras . J. Exp. Biol. 217, 225-234. (doi:10.1242/jeb.092403) Crossref, PubMed, ISI, Google Scholar

Hoppe D, Helfmann S, Rothkopf CA

. 2018 Humans quickly learn to blink strategically in response to environmental task demands . Proc. Natl Acad. Sci. USA 115, 2246-2251. (doi:10.1073/pnas.1714220115) Crossref, PubMed, ISI, Google Scholar

. 2001 Great-tailed grackle (Quiscalus mexicanus), version 1.0 . In Birds of the world (eds

Yorzinski JL, Argubright S

. 2019 Wind increases blinking behavior in great-tailed grackles (Quiscalus mexicanus) . Front. Ecol. Evol. 7, 330. (doi:10.3389/fevo.2019.00330) Crossref, ISI, Google Scholar

. 1995 Controlling the false discovery rate: a practical and powerful approach to multiple testing . J. R. Stat. Soc. 57, 289-300. Google Scholar

Bristow D, Haynes JD, Sylvester R, Frith CD, Rees G

. 2005 Blinking suppresses the neural response to unchanging retinal stimulation . Curr. Biol. 15, 1296-1300. (doi:10.1016/j.cub.2005.06.025) Crossref, PubMed, ISI, Google Scholar

Volkmann FC, Riggs LA, Moore RK

. 1980 Eyeblinks and visual suppression . Science 207, 900-902. (doi:10.1126/science.7355270) Crossref, PubMed, ISI, Google Scholar

. 1994 Bird interactions with utility structures collision and electrocution, causes and mitigating measures . Ibis 136, 412-425. (doi:10.1111/j.1474-919X.1994.tb01116.x) Crossref, ISI, Google Scholar

Marques AT, Batalha H, Rodrigues S, Costa H, Pereira MJR, Fonseca C, Mascarenhas M, Bernardino J

. 2014 Understanding bird collisions at wind farms: an updated review on the causes and possible mitigation strategies . Biol. Conserv. 179, 40-52. (doi:10.1016/j.biocon.2014.08.017) Crossref, ISI, Google Scholar

Moinard C, Statham P, Green PR

. 2004 Control of landing flight by laying hens: implications for the design of extensive housing systems . Br. Poult. Sci. 45, 578-584. (doi:10.1080/00071660400006321) Crossref, PubMed, ISI, Google Scholar

. 1996 Physiological indices of workload in a simulated flight task . Biol. Psychol. 42, 323-342. (doi:10.1016/0301-0511(95)05165-1) Crossref, PubMed, ISI, Google Scholar

. 2002 An analysis of mental workload in pilots during flight using multiple psychophysiological measures . Int. J. Aviat. Psychol. 12, 3-18. (doi:10.1207/S15327108IJAP1201_2) Crossref, Google Scholar

Cross DJ, Marzluff JM, Palmquist I, Minoshima S, Shimizu T, Miyaoka R

. 2013 Distinct neural circuits underlie assessment of a diversity of natural dangers by American crows . Proc. R. Soc. B 280, 20131046. (doi:10.1098/rspb.2013.1046) Link, ISI, Google Scholar

. 2016 Eye blinking in an avian species is associated with gaze shifts . Scient. Rep. 6, 32471. (doi:10.1038/srep32471) Crossref, PubMed, ISI, Google Scholar

. 2017 Half-blind to the risk of predation . Front. Ecol. Evol. 5, 131. (doi:10.3389/fevo.2017.00131) Crossref, ISI, Google Scholar

. 1989 Eye movements and blinks: their relationship to higher cognitive processes . Int. J. Psychophysiol. 8, 35-42. (doi:10.1016/0167-8760(89)90017-2) Crossref, PubMed, ISI, Google Scholar

. 2017 Pigeons (C. livia) follow their head during turning flight: head stabilization underlies the visual control of flight . Front. Neurosci. 11, 655. (doi:10.3389/fnins.2017.00655) Crossref, PubMed, ISI, Google Scholar


First evidence of sleep in flight

For the first time, researchers have discovered that birds can sleep in flight. Together with an international team of colleagues, Niels Rattenborg from the Max Planck Institute for Ornithology in Seewiesen measured the brain activity of frigatebirds and found that they sleep in flight with either one cerebral hemisphere at a time or both hemispheres simultaneously. Despite being able to engage in all types of sleep in flight, the birds slept less than an hour a day, a mere fraction of the time spent sleeping on land. How frigatebirds are able to perform adaptively on such little sleep remains a mystery.

It is known that some swifts, songbirds, sandpipers, and seabirds fly non-stop for several days, weeks, or months as they traverse the globe. Given the adverse effect sleep loss has on performance, it is commonly assumed that these birds must fulfill their daily need for sleep on the wing.

Half-awake or fully awake in flight?

How might a bird sleep in flight without colliding with obstacles or falling from the sky? One solution would be to only switch off half of the brain at a time, as Rattenborg showed in mallard ducks sleeping in a dangerous situation on land. When sleeping at the edge of a group, mallards keep one cerebral hemisphere awake and the corresponding eye open and directed away from the other birds, toward a potential threat. Based on these findings and the fact that dolphins can swim while sleeping unihemispherically, it is commonly assumed that birds also rely on this sort of autopilot to navigate and maintain aerodynamic control during flight.

However, it is also possible that birds evolved a way to cheat on sleep. The sleep researcher's and colleagues' recent discovery that male pectoral sandpipers competing for females can perform adaptively for several weeks despite sleeping very little raised the possibility that birds simply forgo sleep altogether in flight. Consequently, evidence of continuous flight is not by default evidence of sleep in flight: Without directly measuring a bird's brain state, previous claims that birds sleep in flight remain mere speculation.

Flight data recorder catches birds napping on the wing

To actually determine whether and how birds sleep in flight, the researchers needed to record the changes in brain activity and behavior that distinguish wakefulness from the two types of sleep found in birds: slow wave sleep (SWS) and rapid eye movement (REM) sleep. Niels Rattenborg teamed up with Alexei Vyssotski (University of Zurich and Swiss Federal Institute of Technology, ETH) who developed a small device to measure electroencephalographic changes in brain activity and head movements in flying birds.

In collaboration with the Galápagos National Park and Sebastian Cruz, an Ecuadorian seabird biologist, the team focused on great frigatebirds nesting on the Galápagos Island. Frigatebirds are large seabirds that spend weeks flying non-stop over the ocean in search of flying fish and squid driven to the surface by predatory fish and cetaceans. The researchers temporarily attached the small "flight data recorder" to the head of nesting female frigatebirds. The birds then carried the recorder during non-stop foraging flights lasting up to ten days and 3000 kilometers. During this time, the recorder registered the EEG activity of both brain hemispheres and movements of the head, while a GPS device on the birds' back tracked their position and altitude. After the birds were back on land and had had some time to recover, they were re-caught and the equipment was removed. Bryson Voirin, a post-doc and co-first author on the paper with Rattenborg observed that, "Like many other animals in the Galápagos Islands, the frigatebirds were remarkably calm and would even sleep as I approached to catch them for the second time."

The flight data recorder revealed that frigatebirds sleep in both expected and unexpected ways during flight. During the day the birds stayed awake actively searching for foraging opportunities. As the sun set, the awake EEG pattern switched to a SWS pattern for periods lasting up to several minutes while the birds were soaring. Surprisingly, SWS could occur in one hemisphere at a time or both hemispheres together. The presence of such bihemispheric sleep indicates that unihemispheric sleep is not required to maintain aerodynamic control. Nonetheless, when compared to sleep on land, SWS was more often unihemispheric in flight. By carefully examining the movements of the frigatebirds, the researchers discovered clues to why they sleep unihemispherically in flight. When the birds circled on rising air currents the hemisphere connected to the eye facing the direction of the turn was typically awake while the other was asleep, suggesting that the birds were watching where they were going. "The frigatebirds may be keeping an eye out for other birds to prevent collisions much like ducks keep an eye out for predators", says Rattenborg.

In addition to engaging in both types of SWS in flight, on rare occasions, bouts of SWS were interrupted by brief episodes of REM sleep. Although this finding may seem remarkable to scientists who study sleep in mammals, based on Rattenborg's experience with birds, he was not that surprised. In contrast to mammals, wherein episodes of REM sleep are long and accompanied by a complete loss of muscle tone, REM sleep episodes only last several seconds in birds. In addition, although a reduction in muscle tone can cause the head to drop during avian REM sleep, birds are able to stand (even on one leg) during this state. Similarly, when frigatebirds entered REM sleep their head dropped momentarily, but their flight pattern remained unchanged.

Ecological demands require full attention 24/7 at sea

Perhaps the greatest surprise was that despite being able to engage in all types of sleep on the wing, on average frigatebirds slept only 42 minutes per day. In contrast, when back on land they slept for over twelve hours per day. In addition, episodes of sleep were longer and deeper on land. Collectively, this suggests that frigatebirds are actually sleep deprived in flight. "Why they sleep so little in flight, even at night when they rarely forage, remains unclear", says Rattenborg. As previous studies have shown that frigatebirds follow ocean eddies predictive of good foraging conditions throughout the day and night, perhaps this is what they are up to. Interestingly, the low amount of sleep in flight suggests that this task requires more attention than that afforded by sleeping with one half of the brain at a time. As such, frigatebirds face ecological demands for full attention 24/7 while at sea.

In the long term, Rattenborg hopes to determine how frigatebirds are able to sustain adaptive performance on such little sleep. People will fall asleep driving a car after losing just a few hours of sleep, even when fully aware of the dangers and struggling to keep themselves awake. "Why we, and many other animals, suffer dramatically from sleep loss whereas some birds are able to perform adaptively on far less sleep remains a mystery", notes Rattenborg. Reconciling the findings from frigatebirds with the wealth of evidence underscoring the importance of sleep in other animals may provide new perspectives on our understanding of sleep and the consequences of its loss.

Original paper:

Niels C. Rattenborg, Bryson Voirin, Sebastian M. Cruz, Ryan Tisdale, Giacomo Dell'Omo, Hans-Peter Lipp, Martin Wikelski, Alexei L. Vyssotski

Evidence that birds sleep in mid-flight.

Nature Communications 2016, 7:12468 (doi: 10.1038/ncomms12468 open access)

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


Rose-Breasted Grosbeak

Rose-breasted grosbeaks are seed-eating birds that breed in cool-temperate North America and migrate to spend winter in tropical America. These birds have large dusky horn-colored beaks, and their feet and eyes are dark. Adult males in breeding plumage have a black head, wings, back, and tail, and a bright rose-red patch on their breast the wings have two white patches and rose-red linings. Their underside and rump are white. Males in nonbreeding plumage have largely white underparts and cheeks. The upperside feathers have brown fringes, and most wing feathers white ones, giving a scaly appearance. The bases of the primary remiges are also white. The coloration renders the adult male rose-breasted grosbeak (even while wintering) unmistakable if seen well. Adult females have dark grey-brown upperparts, a buff stripe along the top of their head, and black-streaked white underparts, which except in the center of the belly have a buff tinge. The wing linings are yellowish, and on the upper wing are two white patches like in the summer male. Immature birds are similar, but with pink wing-linings and less prominent streaks and usually a pinkish-buff hue on the throat and breast.



Comments:

  1. Beowulf

    and here there are really cool ones

  2. Fejas

    what in such a case to do?

  3. Helaku

    Test and niipet!

  4. Tokinos

    I think you are not right. I can prove it. Write in PM.

  5. Elston

    Thank you and write again, but the map is not enough!



Write a message