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plumage,of birds: see feathersfeathers,
outgrowths of the skin, constituting the plumage of birds. Feathers grow only along certain definite tracts (pterylae), which vary in different groups of birds.
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the feathery covering of birds. It protects the body from chilling, streamlines body contours, and increases the surface of the wings and tail for flight.
Plumage consists of feathers varying in structure. There are contour feathers, down feathers, filoplumes, powder downs, and bristles. Pterylae, areas of skin on which feathers grow, alternate with apteria, skin areas that lack feathers but are usually covered by them. Only Struthionidae, penguins, and screamers have feathers that are evenly distributed over the skin. Usually the downy feathers and powder downs are hidden by the vanes of the contour feathers that lie on one another, but in some birds, such as the vulture, the powder downs are exposed. In herons, owls, goatsuckers, swifts, and many passerines the powder downs are located on the apteria; in Crypturiformes they are located only on the pterilae. In the majority of other birds the powder downs are found over the entire body.
Plumage is renewed periodically, usually annually, by molting. The colors of plumage are due to the presence of pigments and structural properties.