In a typical feather, barbs extend outward from the distal portion of the shaft, or rachis smaller crosslinking barbules and hooks interlock neighboring barbs, forming a web that gives the feather both strength and flexibility. Down feathers, or plumulae, the first plumage of young birds and the protective undercoat of aquatic birds, lack these interlocking projections. Specialized feather forms are found in crests, top-knots, ruffs, and tail feathers. Bristles are modified feathers. The colors red, yellow, brown, and black are caused by pigment in the feathers. There are no blue pigments, and green and violet are rare however, these colors, as well as iridescent effects, are caused by the reflection and diffraction of light.
Feathers are lightweight, durable, and in some cases waterproof. They have protective and decorative functions, but, aside from their role in bird flight , their most important capacity is heat retention. Feathers are believed to have evolved from reptilian scales in Mesozoic times, but little is definitely known about how they arose, and the feathers of Archaeopteryx and other early birds may have been too weak to be useful for flight. A number of feathered dinosaurs are known from the fossil record one, Yutyrannus huali, was quite large (30 ft/9 m long) and had filamentlike feathers.
Feathers have been used by humans from ancient times for millinery and other ornamental purposes. The indiscriminate hunting of certain birds for their feathers has resulted in their near extinction it is now prohibited by law in the United States.
See T. Hanson, Feathers (2011).
See more Encyclopedia articles on: Zoology: General
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