Feather (bird anatomy) - biology.

Feather (bird anatomy) - biology. I INTRODUCTION Feather (bird anatomy), horny outgrowth of skin peculiar to the bird but similar in structure and origin to the scales of fish and reptiles and analogous to the hair of mammals. Feathers serve as protection against water and cold, as an aid in flight, and as sex differentiators. II STRUCTURE AND APPEARANCE A feather consists of two principal parts, the axis, or spinelike central structure, and the barb, or side branch of the stem. The axis is divided into a bare, hollow portion known as the quill and a barb-bearing, solid part called the shaft. The base of the quill is rooted in a small sac of the skin and has a tiny opening for the entrance of the nutritive pulp, which feeds the feather while it is growing. The barbs, which all together form the vane or fringe, are linked to each other by pointed barbules, or smaller barbs, which may be again interlocked by minute hooks. The most conspicuous feathers on a bird, the contour feathers, or pennae, make up the large feathers of the wings and tail. Another type, called down feathers, consists of long, loose, soft plumes. About the base of the contour feathers are found small growths of a third type called filoplumes, which are small, simple, hairlike feathers with a long shaft and a rudimentary brush of barbs. Powder down feathers are stunted feathers that dry up and disintegrate, leaving a dry, waxy powder that spreads over the rest of the plumage. The feathers of the male bird may be different in appearance from those of the female bird of the same species. These differences are due mainly to the sex hormone produced by the ovary or testis. In most birds, as in the indigo bunting, genes determine plumage, and in others, as the pheasant, the difference results from a combination of genetic and endocrine factors. Elaborate feathers, such as those in a peacock's tail, evolve due to female preference when choosing mates and to competition between males for mates. III USES OF FEATHERS Feathers have been used by humans in three principal ways: as writing implements, in upholstery and bedding, and as ornaments in clothing and costumes. The demand in the United States and elsewhere for feathers to be used for ornamentation led to great slaughter of birds and the extinction or near extinction of several species. To promote legislation restricting the killing of birds for their feathers, various societies have been formed. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.