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outgrowths of the skin, constituting the plumage of birds. Feathers grow only along certain definite tracts (pterylae), which vary in different groups of birds. Feathers develop from tiny projections of tissue (papillae) embedded in follicles and nourished by blood vessels in the dermis. When the feather is full grown, the blood supply is discontinued and the central shaft becomes hollow. A secretion of the thyroid gland stimulates the papilla to develop a new feather when one has been molted or pulled.

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 flightflight,
sustained, self-powered motion through the air, as accomplished by an animal, aircraft, or rocket. Animal Flight

Adaptation for flight is highly developed in birds and insects. The bat is the only mammal that accomplishes true flight.
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, 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 ArchaeopteryxArchaeopteryx
[Gr.,=primitive wing], a 150 million-year-old fossil animal first discovered in 1860 in the late Jurassic limestone of Solnhofen, Bavaria, and described the following year.
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 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).

References in classic literature ?
He wore a profusion of ribbons on his garment, and gold lace on his hat, which was also encircled by a gold chain, and surmounted with a feather.
The nest which had been advertised had not included feathers for quite so many birds as there were in this family.
Now came some more chamber-maids and retouched the sidewalk, and afterward wiped the marble steps with damp cloths and finished by dusting them off with feather brushes.
I could see that if I wanted to go a-visiting any distance from home, and the wind was ahead, I might have to wait days, maybe, for a change; and I could see, too, that these things could not be any use at all in a gale; if you tried to run before the wind, you would make a mess of it, for there isn't anyway to shorten sail - like reefing, you know - you have to take it ALL in - shut your feathers down flat to your sides.
No -- better still, he would join the Indians, and hunt buffaloes and go on the warpath in the mountain ranges and the trackless great plains of the Far West, and away in the future come back a great chief, bristling with feathers, hideous with paint, and prance into Sunday- school, some drowsy summer morning, with a blood- curdling war-whoop, and sear the eyeballs of all his companions with unappeasable envy.
Tom was packed in ten minutes, all except what his aunt and Mary would finish up for him; then we waited ten more for her to get cooled down and sweet and gentle again; for Tom said it took her ten minutes to unruffle in times when half of her feathers was up, but twenty when they was all up, and this was one of the times when they was all up.
What are you layin' on your good bed in the daytime for, messin' up the feathers, and dirtyin' the pillers with your dusty boots?
Georgiana sat on a high stool, dressing her hair at the glass, and interweaving her curls with artificial flowers and faded feathers, of which she had found a store in a drawer in the attic.
A minute previously she was violent; now, supported on one arm, and not noticing my refusal to obey her, she seemed to find childish diversion in pulling the feathers from the rents she had just made, and ranging them on the sheet according to their different species: her mind had strayed to other associations.
Then she ran down the path through the other door and then into the orchard, and when she stood and looked up there was the tree on the other side of the wall, and there was the robin just finishing his song and, beginning to preen his feathers with his beak.
And if you were shown a flock of birds, unable to fly, and were set upon them to strip them of their feathers for your own advantage, you would set upon the birds of the finest feathers; would you not?
Once more the little room, with its open corner cupboard, and its square-backed chairs, and its angular little staircase leading to the room above, and its three peacock's feathers displayed over the mantelpiece - I remember wondering when I first went in, what that peacock would have thought if he had known what his finery was doomed to come to - fades from before me, and I nod, and sleep.