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Feathers are good for flying, but they help birds do a lot more than just soar through the skies.

Hosted by: Hank Green

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Sources:
Sources:

Sounds
http://rspb.royalsocietypublishing.org/content/277/1683/835
https://academy.allaboutbirds.org/feathers-article/6/
http://www.sibleyguides.com/2015/04/the-mysterious-sounds-of-the-american-woodcock/
https://www.smithsonianmag.com/science-nature/these-birds-can-sing-using-only-their-feathers-180958678/

Muffle
https://www.cam.ac.uk/research/news/silent-flights-how-owls-could-help-make-wind-turbines-and-planes-quieter
https://www.aps.org/units/dfd/pressroom/news/2013/upload/The-Secrets-of-Owls-Near-Noiseless-Wings.pdf
https://www.technology.org/2017/08/14/engineer-looks-to-owl-wings-for-bio-inspired-ideas-for-quieter-aircraft-wind-turbines/
http://rsfs.royalsocietypublishing.org/content/7/1/20160078

Hearing
https://www.utsc.utoronto.ca/~amason/courses/coursepage/presentations/files/Directional%20hearing%20in%20the%20barn%20owl.pdf
https://www.americanscientist.org/article/how-the-owl-tracks-its-prey
https://www.researchgate.net/publication/10580236_Morphometry_of_Auricular_Feathers_of_Barn_Owls_Tyto_alba
http://scienceblogs.com/tetrapodzoology/2008/07/14/owl-ear-tuft-mystery/
https://pdfs.semanticscholar.org/34d4/959e835eeeb5baf00ebdd7e9754fcb3bec32.pdf

Stomach
https://britishbirds.co.uk/wp-content/uploads/article_files/V49/V49_N11/V49_N11_P432_435_A075.pdf
http://www.bioone.org/doi/abs/10.1676/16-196.1
https://web.stanford.edu/group/stanfordbirds/text/essays/Eating_Feathers.html

Fishing
https://sora.unm.edu/sites/default/files/journals/nab/v029n03/p00652-p00654.pdf
https://deepblue.lib.umich.edu/bitstream/handle/2027.42/71734/j.1474-919X.1988.tb00953.x.pdf?sequence=1
http://www.heronconservation.org/styled-5/styled-12/

Water transport
https://www.audubon.org/news/why-would-bird-carry-water-its-feathers
https://www.tandfonline.com/doi/pdf/10.1080/00445096.1973.11448511
https://www.researchgate.net/publication/242287754_The_water_holding_mechanism_of_sandgrouse_feathers
https://books.google.com/books?id=YvmC2sU-LqgC&pg=PA138

Snowshoe
https://sora.unm.edu/sites/default/files/journals/condor/v079n03/p0380-p0382.pdf
https://www.audubon.org/news/ptarmigan-may-be-tops-adapting-winter-weather

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Images & Sounds:
https://www.flickr.com/photos/31267353@N03/29768530604/in/photolist-Mmxv2E-MmxuRu-rEy34Z-FtHjP
https://www.xeno-canto.org/248573
https://commons.wikimedia.org/wiki/File:Woodcock.jpg
https://www.xeno-canto.org/133923
https://www.flickr.com/photos/70804987@N00/4804568378
SciShow is supported by Skillshare. [INTRO ♪].

You don’t need to know much about birds to realize that their feathers are pretty awesome. They come in a dazzling array of shapes and colors, they keep birds warm and dry, and of course, allow them to fly.

And since feathers are made out of the protein keratin, they’re also super strong and mostly waterproof. But that’s not all they can do. Thanks to millions of years of evolution, there are other, lesser-known functions of feathers that are equally cool, and many of them give certain birds unique abilities.

Here are seven of them. We generally think of birds using their mouths to make sounds—or, more accurately, their vocal organs, called syrinxes. But feathers can also do the trick.

One example is with male club-winged manakins, super cute little birds that live in South America. They use their feathers for mating calls as part of an elaborate dance. Their club-shaped wings include a few special feathers, which happen to be shaped so that they rub against each other and produce high-pitched sounds—like adorable car horns.

Ornithologist Kim Bostwick discovered this unique ability about a decade ago after seeing video of the birds’ courtship behavior slowed way down. She realized that individually, moving the feathers did very little acoustically. But when they moved together very quickly, one feather, which is bent, strikes another, which has seven ridges on it.

This ultimately allows the feather to vibrate at 1500 cycles per second and create that high pitch. The mechanism is essentially the same as what crickets use to create their chirps, or what scientists call stridulation. Other birds make audible noises with their feathers to attract mates, too, but use other methods.

For example, male American woodcocks fly extremely high in the air and flap their wings very fast, making characteristic twittering sounds. This is thought to be from what’s called aeroelastic flutter, which basically comes down to air moving past feathers. In the woodcock’s case, they have very narrow feathers at the edge of their wings, and the gaps in-between them create a whistling sound.

Hummingbirds also make noise this way, using their tail feathers. If enough feathers vibrate at the same frequency, it can increase the volume of the sound. Next, instead of creating sound, some feathers play an important role in dampening it.

If you’re a bird, especially a fairly large one, flapping your wings or even just gliding can make a lot of noise. And if you’re trying to hunt, that racket is not exactly helpful. Most birds of prey, or what ornithologists call raptors, are usually such fast flyers that sound isn’t necessarily an issue.

But owls move much more slowly, so stealth is key. The secret to their near-silent hunting ability is three special feather features. First, there are serrations, or comb-like structures, right where air first hits the wing.

These break up the air as it moves across the wing, reducing turbulence and overall noise. Then, at the trailing edge, or rear part of the wing, there are wispy fringes, which scientists think help smooth the airflow as it comes off the wings. Finally, a soft, velvety covering on the tops of the wings forms a microscopic mesh that is exceptionally good at absorbing sound.

These strategies are so effective at noise-reduction that engineers are now borrowing the designs for use on planes and wind turbines, and they’ve already had some success with 3D-printed, owl-inspired coatings in preliminary tests. But stealth may not be the only reason driving the need for silence. Biologists studying owl evolution think keeping quiet is important not just to avoid tipping off prey, but also for accurately detecting it, which is largely done by hearing.

And hearing also depends on, what else? Feathers! Feathers are critical for owl hearing, but it’s not in the way you might think.

The iconic ear tufts may look like ears, but scientists aren’t sure what they do—maybe they’re used as camouflage, or some kind of visual display. But either way, they are not for listening. Instead, hearing depends on owls’ heart-shaped faces and on what are called facial discs: the concave shape around each of their eyes.

This area is lined with stiff reflector feathers, which amplify and direct sound waves into owls’ ears. They’re basically like radar dishes. These feathers have abnormally thick central shafts and are packed extremely close together, just about as close as they physically can be.

That makes for a good reflecting surface, and it allows owls to hear and pinpoint the source of very soft noises—which is kind of their thing. The special feather-lined discs are thought to be one reason why owls are such expert hunters. After all, they’re really good at nabbing mice or voles, or whatever might look tasty, and most of them do it at night.

Most other raptors hunt during the day and have excellent vision. A few also have facial discs, which helps them hear better, but they’re less pronounced than in owls. Owl vision isn’t too shabby, either, but biologists have found that, thanks to their superior hearing, they can still hunt even in complete darkness.

Without these facial feathers, though, they tend to misjudge the location of quiet sounds—at least, according to one experiment with a barn owl. While owl feathers are finely tuned for nocturnal hunting, birds known as grebes use their feathers in a less impressive, but still important way: They eat them. Specifically, to slow digestion and prevent pokey fish bones and insect or crustacean parts from damaging their digestive tracts.

This is maybe the strangest feather function, and grebes are the only birds known to do it. But it does have some logic. Typically, birds that have trouble breaking down hard foods will eat tiny stones so that the rocks can grind up the food in their gizzards, which make up one part of a bird’s stomach.

It’s kind of like having a mortar and pestle in your body, because nature is just really hardcore that way. But grebes, for unknown reasons, don’t do this, and just rely on chemical digestion in their stomachs. Scientists think the feathers—which can fill up to half of the gizzard—do two things.

First, they slow digestion down, forming feather balls that the bird will eventually cough back up. That gives things like bones time to dissolve. A second, smaller feather ball also forms in a later part of the digestive tract called the pyloric pouch.

This is the last stage before food moves into the bird’s intestines, so any non-dissolved sharp bits could be a problem if they make it through. So the feathers here are thought to filter out all the possibly dangerous items. This strange habit, then, of self-plucking and consumption, seems to be related to the grebe’s diet.

But that does not make it any less bizarre. Other water-based birds use their feathers in some strange ways. Black herons in Africa, for example, fish with a technique known as canopy feeding.

In this method, the bird covers its head and wraps its wings in a circle. It fans out its dark feathers to form an umbrella, which it then hunts under—like a little fishing hut. The exact reason for the canopy is unclear, but some scientists think this method scares off tiny fish, while leaving the larger and medium-sized ones to the herons.

It’s also possible the shade draws fish in or reduces glare. Green herons, which live in North America and Central America, have also been known to drop feathers onto the water to attract fish. This kind of bait-fishing doesn’t always work, and isn’t restricted to feathers, but it is a relatively rare case of a bird using a tool.

One of the more impressive feather adaptations belongs to the sandgrouse, a desert-dwelling, pigeon-like bird. Since water is at a premium, and baby birds can’t yet fly, adult birds—usually the males—use specialized belly feathers to pick up water and ferry it back to their nests. Which is a little bit adorable.

Males collect water by walking into a shallow pool, and in bursts, rocking their bodies back and forth—a filling process that can take 15 minutes. The feathers themselves pick up water thanks to their unique structure. When dry, the feathers have coiled barbules, the secondary branches on feathers.

But when they get wet, the barbules naturally uncoil, and their hair-like extensions pull in water through capillary action. That's when water sticks to the walls of a thin tube enough to pull it up, despite gravity. While it doesn’t sound like a lot, a single bird can pick up 40 milliliters this way—plenty for a baby bird.

Once the adult flies back, chicks then kind of “milk” the feathers for their liquid. Biologists studying sandgrouse suspect that one advantage to this method is that the adults don’t have to sacrifice any of their own water intake to feed the chicks. They can just soak their belly feathers, and avoid any messy parent-child competition.

Finally, most birds have scales on their feet, but a few have feathers, including northern birds called ptarmigans, which use them like snowshoes. The added feathers quadruple the area of their foot, spreading out the bird’s weight and making it less likely they’ll sink down into the snow. We know this thanks to one curious Canadian physiologist back in the 1970s, who tested this function in three different species of ptarmigans.

He plucked the foot feathers from some birds, and left them intact in others, then measured how much each sank into the snow. He found that feathering reduced the sinking by about half, and concluded that this feather adaptation probably helps the birds save a lot of energy when traveling. If that’s not amazing enough, though, it turns out that some species grow these feathery snowshoes every year.

In the summer, they don’t need the feathers, so they molt them off. But by the time winter rolls around, they’ve grown out their claws and sprouted bright, white feathery shoes, which scientists think might also help keep their feet warm. Clearly, there’s a lot more to feathers than just flight—as cool as flying is.

Feathers are wonderful sound makers, they’re water bottles, and they even come in handy as snowshoes. As a bonus for us, there's also plenty of ways we can benefit from some of these remarkable adaptations—like owls and their ultra-stealthy feathers. Which means we’ll have much more to thank birds for.

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