Skin and Feathers of Birds

Birds have a sensitive skin that allows them to feel and sense pressure, heat, and cold. The feathers of a bird grow from the inner layer of skin (the dermis). Feathers provide assistance in flight, insulation from cold, waterproofing, and—in some cases—camouflage. In some species, the feathers can also indicate sex and mating status.

There are 8 main types of feathers, including 3 types of contour feathers, semiplumes, down feathers, natal down, bristles, and filoplumes. Contour feathers cover most of a bird's body and are used for flight. Each contour feather has a central hollow quill that starts at the base of the feather and connects to a central shaft known as the rachis. Branching out from the rachis are vanes which, in turn, support the barbs. Each barb has many smaller, hooked segments known as barbules. The barbules hook together, making the feather strong and uniform. There are 3 types of contour feathers: body feathers, flight feathers (wing feathers called remiges and tail feathers called retices), and ear coverts.

Down feathers are small and soft. They grow between the contour feathers and keep the bird warm. Adult down feathers are structurally different than the down feathers found on chicks (natal down feathers). Some newly hatched chicks have only natal down feathers. Anyone who has ever slept under a down comforter knows how soft and warm these feathers are.

Sensory bristles are located around a bird's eyes, nostrils, and mouth. They play a role in the sense of touch.

Filoplume feathers are long and shaped like hairs. Their function is not fully understood, although it is probable that some birds (for example, psittacines) use these feathers to sense vibrations and changes in pressure—abilities that would be very helpful during flight. Not all species of birds have filoplume feathers.

Preening is how birds maintain their feathers. They use their beaks or bills to clean their feathers and keep them aligned correctly. At the same time, some birds waterproof their feathers using an oil produced by a gland (called the uropygial or preen gland) located near the tail. Other birds use a powder formed by powder down feathers to waterproof their feathers.

Flight and normal rubbing against objects in their environment can damage and wear feathers. Molting is the process by which birds renew their feathers. During the molt, an old feather is pushed out of the skin by the growth of new feather cells at the base of the old feather. The weight of a feather has nothing to do with its loss; it is the growth of a new feather that dislodges the old one. In most birds, feathers are discarded on both sides of the bird simultaneously to avoid problems with flying. Most birds replace all their feathers at least once a year, most often after the breeding season. Some birds molt more frequently. No matter how frequently a bird molts, their bodies naturally time the loss of feathers in such a way that the bird always has sufficient feathers for warmth and flight.