Feathers are composed of phi-keratin, which is not known to occur in any nonbird animal tissue except alligator claws.
We mammals are a varied class of animals coming in myriad shapes and sizes, from bats to whales, giraffes to platypuses, lions to human beings. The tiniest shrews are of similar size to hummingbirds, but the largest whales are orders of magnitude larger than the biggest ostriches or even the most gigantic birds that ever lived, the moas and elephant birds. All birds stand or perch on two feet, and although a few, like the kiwi and ostrich, have only vestigial wings, the overall bird shape is distinctive.
Bird bodies are covered by and get their distinctive shape from feathers — a unique feature found nowhere else in the animal kingdom. What mammal could truly be called “resplendent” or “scintillant,” or be justifiably named for any of the gems common in hummingbird names — ruby, amethyst, topaz, emerald, sapphire, or garnet?
Small wonder our depictions of angels portray them bearing the wings of birds. And small wonder that when we see birds, our minds are filled with questions.
Q What are feathers made of?
A Feathers are features unique to and universally found in all species of birds. Each one grows out of a specialized structure called a papilla. Human hair also grows out of papillae — biologists are still researching how similar these structures may be, and how similar feathers may be to reptilian scales. Compared to scales, feathers are much softer and more flexible, are extremely lightweight but strong, and provide excellent insulation against excessive cold and heat.
Intuitively, it seems like feathers must have started out as scales that evolved to become frayed. But developmental biologists point out that feathers begin growing as tubular structures quite different from scales. Scientists are still debating why feathers evolved — whether they were originally for insulation, flight, display, or some other function. There are lots of fossils that suggest many feathered dinosaurs did not fly.
Feathers are composed of phi-keratin, which is not known to occur in any nonbird animal tissue except alligator claws.
The largest feathers are peacock tail feathers, which can be as long as 5 feet (1.5 m). The tiniest feathers are the eyelid feathers of the Bee Hummingbird of Cuba, measuring a mere 1/63 of an inch (0.40 mm).
Q How many feathers does the average bird have?
A People have not counted feathers on a great many species, but during the 1930s, a few scientists took the time to count the contour feathers of several dead birds. (Contour feathers include the external body feathers but not other feathers, such as down.) They had to delicately pluck the feathers and count them one by one.
One Ruby-throated Hummingbird had 940 contour feathers, and one Tundra Swan had 25,216. The latter, so far, represents the most feathers ever counted on an individual bird. Fully 80 percent of them (20,177 to be exact) were on the head and neck — the parts of a swan that are submerged in water when the bird is feeding. Those are very tiny compared with the contour feathers on the rest of the body. Imagine counting them all!
The number of feathers may also vary seasonally. One researcher counted the feathers on a few White-throated Sparrows. Those collected in winter averaged 2,500 contour feathers; those collected in summer averaged only 1,500.
A remarkable diversity of feathers exists for many purposes.
Flight: The feathers of the wings are strong, stiff, and lightweight enough to propel and provide lift to the bird in flight, and feathers of the tail are strong and stiff enough to help even the fastest falcons steer. The feathers on the head and body are arranged to streamline the body for flight and when facing a stiff wind.
Protection: Outer feathers give birds a fairly waterproof shell that protects their skin from rain and snow, as well as sunburn. Beneath the outer feathers, down feathers trap and hold in body heat. Some body downs are adapted for insulating not just the bird but also her eggs, which do not generate their own heat. Many female waterfowl pluck down feathers from their bellies to line their nests.
In the most famous case, the exquisite down of female eiders insulates the eggs from the permafrost below even as the incubating duck protects them from frigid air temperatures above. When she leaves the nest to feed, she blankets the eggs in this down to hide them and keep them warm and dry.
Feathers often help camouflage birds, such as the mottled brown plumage of an American Woodcock that blends in with the forest floor.
Attracting a Mate: Color patterns on feathers can have the opposite function of camouflage. Some brightly colored plumage makes a bird highly visible. Many birds have specialized feathers that appeal to mates.
The back feathers of many species of egrets and herons in breeding plumage are long and wispy. The barbules of the long tail feathers of male Indian Peafowl are decorated with a beautiful “eye.” The Resplendent Quetzal has tail streamers (actually elongated rump feathers) that may be nearly twice as long as its body.
Special Functions: The tail feathers that brace woodpeckers, swifts, and some other birds against trees or other hard structures are very stiff.
Some insect-eating birds have specialized feathers called rictal bristles near their beaks, with an extremely stiff shaft and no barbs. These may help funnel insects into the bird’s mouth or provide extra tactile sensitivity as do cat whiskers. Experimental data indicates that they also protect the bird’s eyes from debris as it captures moths and other large, scaly insects in flight. Many birds have modified wing or tail feathers that allow them to produce sounds for communication during courtship displays.
Q I was walking with one of my friends when we came upon a random yellow feather. He looked at it for just a second and said it was a flight feather from the left wing of a Northern Flicker. How could he possibly know that?
A Your friend lucked into finding one of the easiest kinds of feathers to identify. He could tell it was a flicker’s feather by the brilliant yellow color on the underside. No other species except the Gilded Flicker, found in Southwestern deserts, shares this. (Feathers from Northern Flickers from the West are red rather than yellow.) He could tell it was a flight feather by its stiff shaft and its length: flight feathers, whether from the wing or the tail, are usually longer than they are wide.
How did he know it was a feather from the wing rather than from the tail? All woodpecker tail feathers are straight, fairly symmetric, exceptionally stiff, and the tip tapers to a point. Wing feathers are more typically feather-shaped, have a very slight curve, and the two vanes (the webbed sides of the feather) are asymmetric: the leading edge of a primary wing feather is narrower than the trailing edge.
So your friend looked at the color and shape to deduce it was a flicker’s wing feather, and put the yellow side down to see which way the feather curved and which was the narrow leading edge to tell whether it came from the right or left wing.
As with any fibers found at a crime scene, feathers can provide important circumstantial evidence in murder investigations.
Prominent Federal Bureau of Investigation (FBI) hair and fiber expert Douglas Deedrick worked extensively with the world’s most famous feather authority, the late Roxie Laybourne, to develop a permanent slide mounting medium that made it possible to establish microscopic data on tens of thousands of feathers. She in turn helped him for decades by examining and identifying feather evidence for FBI cases.
Although feathers aren’t found in nearly as many investigations as other fibers (including hair), her services were used in as many as a dozen robbery, kidnapping, and murder cases each year. She also identified feathers implicated in airplane collisions with birds. Mrs. Laybourne spent her career with the Smithsonian Museum of Natural History, where she could compare feather samples with the huge collection housed there to verify her identifications.
Q Is there a book that teaches how to identify feathers?
A No. Some birds, such as flickers and Blue Jays, have many easily recognized feathers, and some birds have at least a few easy ones. For example, Cedar Waxwing tail feathers are each tipped at the terminal end with a brilliant band of yellow, and Eastern Kingbird tail feathers are tipped with white. But identifying most individual feathers is not nearly that straightforward.
Most owl flight feathers are extremely soft, as if coated with velvet, and their leading primary wing feathers have a stiff “comb” on the leading edge. But it’s tricky to know which owl a given feather might have come from, though size gives some hints. Ducks, shorebirds, and some other water birds have outer feathers that feel waxy. The better you get at bird identification, the more clues you’ll be able to integrate to puzzle out individual feathers. But some feathers may be only identifiable by experts in laboratories.
Q Someone told me there’s no such thing as blue feathers. Is this true?
A Anyone who has ever observed a bluebird or jay knows darned well there are blue feathers. But there is no such thing as blue pigment in feathers. Blue in feathers is a “structural color,” which means the color we see is due to a very special arrangement of keratin and air overlying a blackish pigment. When light bounces off this layer, it appears blue.
If you find a blue feather, check it out! When you hold it so the light bounces off it, it will be bright blue. But when you hold it so it’s backlit, either by the sun or any artificial light, some of the pigment color — a dark brownish gray — will show through.
Budgerigars living in the wilds of interior Australia are mostly green, which is the result of yellow pigments and blue structure. Birds in captivity have been bred for different colors. If a bird’s feathers lack the yellow pigment but maintain the blue structure, they’ll be blue. If they lack the structure but maintain the pigment, they’ll be yellow. And if they’re lacking both the structure and the pigment, they’ll be white.
Iridescence is also caused by feather structure. If you were to grind up a hummingbird’s brilliant throat feathers or the metallic green feathers of a Mallard, you’d end up with a dark gray powder, the color of the feathers’ pigment. But if you ground up some red feathers from a Scarlet Tanager, the powder would be red because those feathers are red from pigment.
Q Early last spring, I saw a bird that was shaped just like a robin running on my front lawn. But it was all white! What was it?
A It was a robin, but unlike most robins, it was white because it was an albino, lacking the pigment melanin. Birds that are normally or seasonally all white, such as swans, egrets, and ptarmigans, are not considered albinos, except in the extremely rare situation in which one also lacks pigment on the beak, feet, and eyes. If your robin had pink eyes, and a pale pinkish bill it was a complete albino. Unfortunately, because complete albinos lack pigment in their eyes, they have no protection from ultraviolet light and tend to become blind, dramatically shortening their lives.
Albinism is rare: one researcher estimated that only about one in 1,800 birds is an albino. In humans, the incidence of albinism is about one in 17,000. Albinism usually results from a genetic mutation that interferes with the production of tyrosinase, the enzyme necessary to produce melanin. Some birds are partially albino, with only certain feathers lacking melanin.
Few if any studies of the distribution or frequency of albinism in birds have been conducted. Some researchers have noted that American Robins and House Sparrows have the highest incidence of albinism of any birds, but this may well be because these two species are both conspicuous in backyards and other habitats where people spend a lot of time, making albinos more likely to be noticed and reported.
Q I love the little red finches that nest in my begonia basket. For some reason, last spring the male was orange, not red, but their babies seemed healthy. What caused his unusual color?
A It was probably caused by his diet. House Finch colors are produced by carotenoid pigments that are incorporated into growing feathers if the birds are eating foods rich in carotenoids, which are found in a variety of wild fruits. In laboratories, when House Finches are fed a simple seed diet, the feathers that grow in after they molt are fairly dull and yellowish. When beta-carotene is added to the diet, the feathers that grow in after they molt are pale orange. And when a red carotenoid found in some fruits called canthaxanthin is added, their next feathers grow in bright red.
In some areas where House Finches have been introduced, such as Hawaii, their natural diet is poor in these pigments and the birds have dull plumage. In other areas, such as Michigan, their feathers can be brilliant.
Brighter males are more attractive to females. The dietary carotenoids that give males these bright colors also give females a good idea of which males are able to find the highest quality food, indicating directly which will be the best providers for their young.
Q I read that Sandhill Cranes don’t have feathers on their faces, but when I saw one up close, those sure looked like red feathers! What gives?
A What you read was true, although the face does indeed look like it’s covered with red feathers, because the skin of the forehead and crown of both sexes is covered with bumpy structures called papilla that look very much like tiny feathers. Blood vessels run very close to the skin’s surface, and when the cranes are engaging in sexual or territorial displays, the papilla become engorged with blood, appearing brilliant red. To further confuse the matter, fine, very thin black plumes lie on top of the red skin, contributing to the feathery appearance.
Brightly colored skin on faces and heads of birds is not uncommon.
Q I just saw a totally bald-headed Blue Jay! At least I think it was a Blue Jay. Why was it missing all its head feathers?
A When some individual birds molt, their head feathers drop out nearly simultaneously. No one has figured out why this happens so frequently in Blue Jays and Northern Cardinals, especially because some individual cardinals and jays seem to molt only a few head feathers at a time, as do other species. Is it significant that these two unrelated species are crested? This is very unlikely, because some crestless birds, such as grackles, sometimes lose all their head feathers, too.
Some people have speculated that bald birds are plagued with mites, but this is unlikely. For several years I had two Blue Jays housed side by side in my rehab facility. Every fall one of them, Sneakers, lost all its head feathers at once while its neighbor, BJ, with whom it shared food, never molted all its head feathers. If one of them had mites, the other probably would have. It seemed to be an individual quirk.
Q Birds always look worse when they leave my birdbath than when they arrived! Why do they bother?
A Wet feathers do indeed look scraggly! Birds bathe to get clean, but when they step out of the bath, their feathers look as unkempt as our hair does just after washing. Birds dip in the water while opening their feathers. If they’re in a completely secluded area and haven’t detected any potential predators lurking about, they may splash and shake and soak through the outer feathers to the down and skin beneath. Then they fly off to preen in a safe hiding spot, nibbling off remaining dirt, parasites, and oils. It is astonishing how quickly the feathers dry and how automatically they resume their shape.
Feathers are a wonderful adaptation for flying creatures. If a bat flying through trees accidentally tore a wing on a branch, the injury could permanently ground it. If a bird were in the same kind of collision, the branch might damage a feather or two but more likely would simply part two feathers, which the bird could realign simply by preening.
Basic Grooming
As wonderful as feathers are, they must be properly groomed to hold up under the rigors of a bird’s daily life. Birds nibble them to realign hooks and barbules to maintain the integrity of the vanes, and in the course of this preening they pick off lice and mites, too. To keep feathers supple and protected from sun, wind, rain, and saltwater damage, most birds have a gland at the base of the tail called a uropygial gland or “preen gland.” During preening, birds nibble at this small, pimplelike structure to squeeze out drops of oil that they work into their feathers to keep them supple and in good condition, as hand lotion can do for our skin. The oil may also foster helpful species of fungus that protect feathers from parasites while helping control harmful fungus growth.
People once believed that the oil secreted by this preen gland directly waterproofed feathers, but when researchers removed the preen gland from ducks, they found that the feathers continued to be waterproof until, over time, they grew brittle and started breaking. Apparently the oil indirectly contributes to waterproofing not by repelling water itself but by helping the feathers to maintain their structure.
Parasite Prevention
Mites and some other ectoparasites eat feathers, damaging hooks and barbules. Preening helps get rid of these pests but often isn’t enough, so many birds engage in additional activities. In one, called “anting,” birds apparently take advantage of the formic acid or another strong chemical in ants to repel mites. There are two techniques for anting. In passive anting, the bird sits still, almost as if in a trance, on an anthill or other spot where ants are swarming, allowing them to crawl through its feathers. In active anting, the bird picks up an ant or other thing with strong chemicals, such as a mothball or cigarette butt, and smears it on its feathers. Sometimes after this active anting, the bird eats the remaining insect.
Birds often sunbathe. As while passively anting, sunning birds seem to enter into a trancelike state; they assume strange positions, often leaning to one side and opening spaces among all their feathers. By raising the temperature of their skin and feathers, they may be driving away parasites or somehow helping to maintain the condition of their feathers. Sun and wear usually take the heaviest toll on wing and tail feathers.
Birds also bathe in water, snow, or dust. It seems odd to us to imagine bathing in dirt, but snow and dust baths can scrape off a lot of parasites.
Drying Out
Anhingas, cormorants, pelicans, storks, vultures, and some other birds sometimes sit for long periods with their wings outstretched to dry them. Anhingas and cormorants spend a lot of time underwater chasing fish, and in both cases feathers can become quite wet, so this activity helps dry them. Anhinga feathers are very permeable to water, much more so than are cormorant feathers. This may help anhingas to swim low and sink into the water more easily, but because the feathers can become very waterlogged, the birds must hold their wings out for longer periods than do cormorants. Vultures often stretch their wings out in the morning. This may help dry feathers that had become wet from rain or dew overnight.
In all these ways, birds keep their feathers in condition, but even with careful maintenance feathers eventually degrade. So birds molt them, replacing each feather usually at least once, often twice, and in some cases three times a year.
Q A junco with a broken tail has been visiting my feeder. One of my friends said it would grow back, but the bird has been here for two months and it looks exactly the same as when it arrived. What is keeping it from growing a new tail?
A If your junco’s tail feathers had been torn out, the bird would have replaced them immediately. However, broken and worn feathers that are intact where they meet the body aren’t replaced automatically until the time of year when the bird would normally replace its feathers. The timing of molting varies among species; your junco should grow in new tail feathers in late summer.
Courting Red-tailed Hawks put on a display in which they soar in wide circles at a great height. The male dives steeply, then shoots up again at an angle nearly as steep. After several of these swoops, he approaches the female from above, extends his legs, and touches her briefly. Sometimes, the pair grab onto one other, clasp talons, and plummet in spirals toward the ground before pulling away from each other.
When I was rehabbing birds, one of my charges was a baby Blue Jay. When he was newly fledged, he spent most of his days outside in my yard. One afternoon when a severe thunderstorm was looming, he was nowhere to be found. When the storm hit, I had to go inside without him. The moment the rain subsided, I headed out and searched my neighborhood, calling for him. When he heard me, he started squawking MAAAA! MAAAAA! from a power line just above a busy bus stop about a block away.
When I reached him, he was sopping wet and bedraggled, his crest and feathers plastered against his skin, looking nothing like a Blue Jay. The dozen people below waiting for a bus stared and laughed as I called, “Come on down, Ludwig!” He flapped his wings and let go of the wire, but his sopping wet wings and tail provided absolutely no lift and he dropped like a rock to the sidewalk, then hopped up to me, still squawking MAAAA! MAAAAA!
The next time he got caught in a storm, he’d figured out that hiding in a sheltered branch is far wiser than sitting out in the open.
