Feather is one of the light, thin growths that cover a bird’s body. All birds have feathers, and they are the only living animals that have them. Feathers consist chiefly of a tough substance called beta keratin. A similar substance called alpha keratin occurs in the hair of mammals and the scales of fish and reptiles. Unlike hair and scales, feathers have a complicated branching pattern.
Kinds and parts of feathers.
Birds can have two chief kinds of feathers: (1) contour and (2) down. The parts of a feather vary, depending on the type of feather.
Contour feathers
grow only in special areas called pterylae. From the pterylae, the relatively large contour feathers fan out to cover the bird almost completely.
A typical contour feather has a broad, flat vane attached to a long central shaft. The shaft consists of two parts. A hollow, rounded base, called the calamus or quill, extends from the vane into the bird’s skin. The solid, tapering upper part of the shaft, called the rachis, runs through the vane. The vane is formed by barbs that branch from the sides of the rachis and barbules that branch from the barbs. Hooks on the barbules link neighboring barbs, giving the vane both strength and flexibility. A sudden blow to the vane is more likely to separate the hooks from neighboring barbs than to tear or break the feather. The bird can refasten the hooks by pressing the barbs together with its beak.
Down feathers,
unlike contour feathers, grow on all parts of a bird’s body. They have an extremely short rachis, so the barbs branch from almost the same point on the shaft. The barbules of a down feather have no hooks, making the vane appear fluffy.
Functions of feathers.
Feathers help most birds to fly, partly by making it easier for them to flap their wings in the air. Feathers also help birds maintain a constant body temperature. For example, down feathers keep birds warm by trapping warm air next to the body. In addition, feathers provide coloring that helps the bird hide from predators (hunting animals). Feathers also are important for communication. For example, many male birds have brightly colored feathers that they display to attract a mate. Although feathers are remarkably durable, they gradually wear out. Most birds shed their feathers and grow a new set at least once a year. This process is called molting. 
How people use feathers.
People have used feathers for a variety of purposes. For hundreds of years, American Indians used feathers to make arrows and headdresses. Until the mid-1800’s, when pens with steel points became popular, most people wrote with quill pens. Today, manufacturers use feathers as stuffing in pillows and furniture. Down feathers provide excellent insulation in jackets, quilts, and sleeping bags. Designers decorate hats and other garments with feathers.
Some uses of feathers, however, have come under heavy criticism. For example, the overuse of feathers for women’s hats has endangered the survival of many kinds of birds. The laws of many countries forbid importing bird feathers.
See also Bird (Feathers); Molting.
