Feather, a horny outgrowth of the skin that forms the body covering, or plumage, of birds. Birds are the only animals to have feathers, and all birds have them. Feathers, like hair, grow from pits called follicles. They do not grow uniformly over the body, but only in certain areas called feather tracts. Nearly all birds molt, or shed their feathers, after the nesting period every year. Some undergo a partial or complete molt again in spring; some molt three times yearly. The young of some birds, such as chickens and certain waterfowl, are hatched already clothed with feathers. Most singing and perching birds are hatched naked.
Some kinds of feathers are used to stuff pillows, cushions, and mattresses. For many years, writing was done with the quills of feathers from geese and other birds. Feathers mounted on the rear of arrow shafts serve as fins, keeping the arrows steady in flight. They serve a similar function on badminton “birds.” Feathers are also made into such products as fans, dusters, and artificial flies used in fishing.
Feathers are popular ornaments on hats. In the early 1900's large hats, lavishly decorated with feathers, were quite popular. The demand for feathers was so great that certain species of birds, including the bird of paradise, the egret, and the ostrich, were threatened with extinction. In the United States federal law now restricts the ornamental use of feathers to those obtained from domesticated birds and from birds, such as pheasants, for which there is a designated hunting season.
A bird's feathers protect its skin from injury and keep it warm and, for most species, dry. They are poor conductors of heat, and they overlap to hold warm air against the body. In cold weather, and when sick, a bird fluffs its feathers to form a thicker warm-air blanket. The insulating effect of feathers enables penguins to survive the bitter cold of antarctic winters, both in air and in seawater.
The feathers of most species are naturally oily. The film of oil keeps birds dry in wet weather and enables waterfowl to swim. Many birds have, at the base of the tail, a gland from which they obtain additional oil to spread on the feathers with the beak while preening.
The wing feathers of most birds provide a light, broad, lifting surface that enables them to fly. The outermost wing feathers are called primaries, and the inner wing feathers secondaries. Short feathers that cover the bases of the primaries and secondaries are called coverts.
Tail feathers serve as rudders and balancers in flight, and are used as brakes in landing. Other feathers, such as those in crests and ruffs, and the ornamental tail feathers of peacocks and turkey gobblers, are used for display in attracting mates. Some birds use feathers in their nests.
There are three types of feathers: contour feathers, down feathers, and filoplumes. Contour feathers are the overlapping feathers that cover the bodies of birds. Down feathers, or plumules, are fluffy feathers that grow under contour feathers. Filoplumes are the fine feathers commonly called “hairs.”
A pinfeather is a growing feather encased in a horny sheath.
A typical contour feather consists of a tapering central shaft, from opposite sides of which grow barbs that form a vane, or web. The quill, the lower part of the shaft, is round and hollow. The upper part, from which the barbs grow, is square and solid. The barbs bear hooks, called barbules, that interlock and hold the barbs together. At the base of the vane of many contour feathers grows a plumy aftershaft.
In most species of birds the males are more brightly colored than the females, and the plumage of the young differs from that of the adults. The brighter plumage of the males helps attract mates. The duller colors of the females and the young help protect them in the nest. Male phalaropes, however, are duller in color than the females. The females do the courting, and the males incubate the eggs. When both sexes share in incubation and care of the young, they are usually colored alike.
Only two kinds of pigment color feathers. Melanin produces black, browns, and dull red. Reds and yellows are produced by lipochromes. Other colors—and the iridescent, metallic colors of many birds—are produced by the refraction and reflection of light. Colored markings have special names. A streak is a bright line following the shaft and spreading out narrowly to the vane on either side. A bar is a bright band crossing the vane and shaft. A spot is a brilliant local area. A margin is a bright line following the outer edge of the vane.