Birds of a Feather

Among living animals, feathers are unique to birds. What is a feather? The most familiar type of feather is a flight feather such as you might see in the wing of a flying bird. Flight feathers look like this:

The feather shaft runs up the middle of the feather, a little off center. On either side of the shaft is the large flat feather vane. This is the flight surface. The vane of the feather is formed of many individual feather barbs. Adjacent barbs are hooked together with a series of microscopic hooks, like velcro. The hooks can be unzipped by pulling gently on the barbs and zipped up again by running the barbs through your fingers. Birds zip their feathers back up by preening -- running the bill over their feathers. Contour feathers, which cover the body of a bird, are similar to flight feathers, but broader and less asymmetrical. On the wings, body and tail, the feathers are precisely overlapped to form a smooth flying surface.

Feathers are made of a very light strong protein called keratin. Birds also have keratin in their beaks and you have a type of keratin in your hair and fingernails. You can feel how a feather works in flight by taking a feather and holding it so that the curved side is up and the narrower part of the feather vane is forward. Then move the feather forward through the air. The feather pulls upward because of a phenomenon called "lift." Lift is generated because when air flows over the feather, it has to go farther as it passes over the curved upper surface. This spreads the air molecules out over a larger surface so that the air over the feather is less dense than the air under the feather. The lift comes from the denser air under the feather pushing it upward. When a bird is in the air, it falls forward to move air past its feathers, but because of the lift produced, it doesn't fall downward. Moving the wings makes the air flow past the feathers even faster. Watch a large bird take off from the ground and notice how hard it has to flap to get high enough into the air so it can begin to fall! If a bird flies into a column of warm air rising from the ground, it may be able to "fall" for a long time without having to flap much.

In some birds, like ostriches, the barbs are not zipped together, so that the feather barbs fall free in a fluffy mass. Would you expect this arrangement to work very well as a flight feather?

Another important kind of feather in birds is the down feather. Down feathers consist of a short shaft and a little plume of unzipped barbs. Down feathers insulate a bird's body to help keep it warm or cool. Other feathers are like bristles and are used as sensory structures, like the whiskers on a cat. Some feathers are used mostly for decoration or attracting a mate.

Kori Bustard
Closer view of head feathers

When you go to the zoo, take a look at the feathers on the Kori bustard. What different kinds of feathers can you see on this bird? How long and wide are its different feathers? How are the feather barbs arranged? Which ones don't have a zipped-together feather vane? How many different kinds of feathers can you find on the African crowned cranes? What do you think might be the function of these different kinds of feathers?

Some birds have what looks like a bright red patch of feathers, but which is actually bare skin through which you can see blood flowing under the skin. This is the case in the red-crowned cranes. What about the red patch on the African crowned crane? Is their red patch skin or feathers? As you look around the zoo, you might make a list of birds with red skin patches.

West African Crowned Crane

African Penguin
Walk over to the aquarium to get a close look at the penguins. How are their feathers similar to or different from those of the white pelicans in the same exhibit? Watch the penguins through the underwater port. Are they swimming or flying?

Bird feathers come in many colors, from inconspicuous browns and grays to dazzling red, blue or green. Feathers are colored in different ways. In some feathers, pigment synthesized by the feather-producing cells is deposited in the feather as it forms. These pigments are different kinds of melanin, which can be either almost black or a reddish-brown color. In some feathers, the bird doesn't make the pigment at all, but gets its feather color out of its food. The feathers of flamingos, ibises and spoonbills are colored with carotenoid (red and orange) pigments found naturally in small crustaceans. However, to keep the feathers of these birds bright, their zoo diet is supplemented with carotenoids.

Some birds change the color of their feathers during the breeding season. For example, here is the breeding plumage of this yellow-billed stork. Also compare this brown pelican in June and September.

Some of the brightest feathers are a sort of optical trick. The surface of the feather has microscopic ridges, like the surface of a CD. Light striking the ridges is broken up like light passing through a prism, and the color of the bird depends on the wave-length of the light leaving the feather. Because this is similar to what happens when light is diffracted through water droplets to make a rainbow, this kind of color is called iridescence (Iris is the Greek goddess of the rainbow). Blue and green feathers are nearly always produced by iridescence, as well as some brilliant reds and yellows. The color of the blue feather above is this kind of color. Curiously enough these feathers must have melanin in order to project their blue structural color. When you go to the zoo, go to see the hyacinth macaw and the scarlet macaw. What kind of color do you think these birds have?

You may have heard the saying "Birds of a feather flock together." What does "of a feather" mean in this saying? Is the saying true? Go to the waterfowl areas near the aquarium, or to the flamingo exhibit, where there are several different species of birds. Do birds with similar feathers seem to keep together? If this is the case, why might it be a useful thing to do? How do you think they recognize each other? In the black-necked swans, the male and female look very much alike. Is this the case in all birds? As you look around the zoo, identify other bird species in which the male and female look similar as well as some bird species in which the male and female look different. Males and females of a species looking different is called sexual dimorphism (di = two; morph = form). Since much of a bird's appearance depends on its feathers, sexual dimorphism is partly due to males and females having different kinds of feathers. Look at the female and male Malaysian fireback pheasant. How are the male's feathers different from the female's feathers?

Although feathers can be used for many other purposes in birds, we usually associate feathers with flying. One feather specialization allows owls to fly very quietly. Look at feathers of the great horned owl. Owls have fringes at the edge of their feathers that muffle the sound of the air passing over the wing as the bird flies low to the ground looking for prey. The feathers around its eyes also help funnel sound towards its ears when it hunts at night. Reducing the sound of its own wings makes it easier for the owl to hear the sounds of potential prey.

To what bird do these feathers belong? Click here to see the bird these feathers came from. What is unusual about these feathers? What other kinds of feathers can you see on this bird?

How many kinds of feathers did you see looking at the birds of the Fort Worth Zoo? Did you discover special kinds of feathers not mentioned in this ZooPax? If you see a specialized feather that you think should be added to this ZooPax, E-mail zoopax@whozoo.org. If your feather suggestion is used, we will give you and your school a credit and identify your contribution.