Animal Diaries Archive

Why a bird has feathers

27 July 2007

Feathers are the most important part of a bird's anatomy. They have so many uses such as for appearance with various colours, patterns and shapes. Feathers also provide the bird with warmth, sun protection, flight and some are even waterproof. Feathers grow quickly because they do not last forever as they become worn and new ones grow to replace old and tired feathers once or twice a year. Birds have different types of feathers each of which are important because they all have their own purpose.

Contour, or vaned, feathers are the most specialized of all feathers. Contour feathers form the outline of the body of a bird, giving it a streamlined look. Included in this group are all of the feathers of the outer body as well as those of the wings and tail. These feathers vary both in thickness and range from the large and stiff flight feathers to the much softer and more delicate feathers that cover and shape the body.

In appearance, semi plumes fall between contour feathers and down feathers, combining a large rachis with downy vanes. Semi plumes are distinguished from down feathers in that the rachis is longer than the longest barbs. They fill in or smooth out the various contours of a bird's body while insulating it, and they also provide flexibility at constricted areas, such as the base of the wings. Semi plumes are usually hidden beneath the contour feathers and are small and often white. Filoplumes are always situated beside other feathers. They are simple, hairlike structures that grow in circles around the base of contour or down feathers. They usually stand up like hairs, and are made up of a thin rachis with a few short barbs or barbules at the tip. Filoplumes are generally smaller than semi plumes and are on half to three fourths of the length of the covering contour feathers.

Down feathers make up the under plumage of a bird. They are usually concealed beneath the contour feathers, and their main function appears to be insulation against the cold weather. Each down feather has a quill and a soft head of fluffy barbs, but there are no barbules and the barbs are not "zipped" together as they are in contour feathers. These feathers are especially numerous in ducks and other water birds. In some species of water birds the adults pluck down feathers from their breasts and use them to line the nest and keep the eggs warm. Chicks of some species are covered with down when they hatch.

Powder down feathers help insulate the bird. Unlike other feathers, powder downs grow continuously. Instead of being moulted, their tips disintegrate into a powdery substance. These feathers grow in dense, yellowish patches on the breast, belly, or flanks of herons and bitterns. In other bird's powder down feathers are more thinly scattered throughout the plumage. Many ornithologists believe that in water birds the powder serves to soak up water, blood, and slime, thus protecting the feathers and making preening easier.