Feather
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'''Feathers''' are one of the epidermal growths that form the distinctive outer covering, or [[plumage]], on [[bird]]s. They are the outstanding characteristic that distinguishes the Class [[Aves]] from all other living groups. Other [[Theropoda]] also had feathers (see [[Feathered dinosaurs]]). Feathers are grouped into feather-tracts.
[[Image:Types de plumes. - Larousse pour tous, -1907-1910-.jpg|thumb|Feather variations]]
==Characteristics==
[[Image:AmazonFeathers.jpg|thumb|right|Detail of the feathers of a young [[Yellow-headed Amazon]].]]
[[Image:Parts of feather modified.jpg|thumb|right|200px|'''Parts of a feather:'''<br/>1. Vane<br/>2. Rachis<br/>3. Barb<br/>4. Afterfeather<br/>5. Hollow shaft, calamus]]
[[Image:A single white feather closeup.jpg|thumb|right|A white feather]]
Feathers are among the most complex structural organs found in [[Vertebrata|vertebrates]]: [[Integumentary system|integument]]ary [[appendages]], formed by controlled proliferation of [[cell (biology)|cell]]s in the [[Epidermis (skin)|epidermis]], or outer skin layer, that produce [[keratin]] [[protein]]s. The β-keratins in feathers, [[beak]]s and claws — and the [[claw]]s, [[scale (zoology)|scale]]s and [[Animal shell|shell]]s of [[reptile]]s — are composed of protein strands [[hydrogen bond|hydrogen-bonded]] into [[beta sheet|β-pleated sheets]], which are then further twisted and [[cross-link|crosslinked]] by [[disulfide]] bridges into structures even tougher than the α-keratins of mammalian [[hair]], [[horn (anatomy)|horns]] and [[hoof]].
Feathers insulate birds from water and cold temperatures. The individual feathers in the wings and tail play important roles in controlling flight. These have their own identity and are not just randomly distributed. Some species have a [[crest (bird)|crest]] of feathers on their heads. Although feathers are light, a bird's plumage weighs two or three times more than its skeleton, since many bones are hollow and contain air sacs. Color patterns serve as [[camouflage]] against [[predator]]s for birds in their habitats, and by predators looking for a meal. As with fish, the top and bottom colors may be different to provide camouflage during flight. Striking differences in feather patterns and colors are part of the [[sexual dimorphism]] of many bird species and are particularly important in selection of mating pairs. The remarkable colors and feather sizes of some species have never been fully explained.
There are two basic types of feather: '''vaned feathers''' which cover the exterior of the body, and ''[[down feathers]]'' which are underneath the vaned feathers. The [[pennaceous feather]]s are vaned feathers. Also called '''contour feathers''', pennaceous feathers are distributed over the whole body. Some of them are modified into remiges, the [[flight feather]]s of the wing, and rectrices, the flight feathers of the tail. A typical vaned feather features a main shaft, called the [[rachis]]. Fused to the rachis are a series of branches, or [[barb (feather)|barb]]s; the ''barbs'' themselves are also branched and form the [[Barbule|''barbules'']]. These barbules have minute hooks called ''barbicels'' for cross-attachment. Down feathers are fluffy because they lack barbicels, so the barbules float free of each other, allowing the down to trap much air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular ''calamus'', or [[quill]], which inserts into a [[Hair follicle|follicle]] in the [[skin]].
[[Image:FeatherLocking.png|thumb|left|Feather microstructure showing interlocking]]
The '''Dyck texture''' is what causes the colors blue and green in most parrots. This is due to a texture effect in microscopic portions of the feather itself, rather than pigment, or the [[Tyndall effect]] as was previously believed. The Dyck texture alters color produced by pigment. Thus, an albino parrot will be white. The spectacular red feathers of certain parrots owe their vibrancy to a rare set of pigments found nowhere else in nature. [[Albinism in birds|Albinism]] is a rare lack of pigment in some or all of a bird's feathers.
In some birds, the feather colors may be created or altered by uropygial gland secretions. The yellow bill colors of many hornbills are produced by preen gland secretions. Other differences that may only be visible in the ultraviolet region have been suggested<ref name=delhey>Delhey K, A. Peters, and B. Kempenaers (2007) Cosmetic coloration in birds: occurrence, function and evolution. Am. Nat. 169:S145-158. [http://www.orn.mpg.de/documents/peters/Delhey_AmNat2007_copy.pdf PDF]</ref> but studies have failed to find evidence.<ref>Delhey, K., A. Peters, PHW Biedermann & B Kempenaers (2008) Optical properties of the uropygial gland secretion: no evidence for UV cosmetics in birds. Naturwissenschaften DOI 10.1007/s00114-008-0406-8 </ref>
[[Image:2 feathers.jpg|200px|thumb|right|Two feathers]]
A bird's feathers are replaced periodically during its life through [[molt]]ing. New feathers are formed through the same follicle from which the old ones were fledged.
Some birds have a supply of [[powder down]] feathers which grow continuously, with small particles regularly breaking off from the ends of the barbules. These particles produce a [[Powder (substance)|powder]] that sifts through the feathers on the bird's body and acts as a waterproofing agent and a feather [[conditioner (chemistry)|conditioner]]. Powder down has evolved independently in several taxa and can be found in down as well as pennaceous feathers. They may be scattered in plumage in the pigeons and parrots or in localized patches on the breast, belly or flanks as in herons and frogmouths. Herons use their bill to break the feathers and to spread them while cockatoos may use their head as a powder puff to apply the powder.<ref name=delhey/> Waterproofing can be lost by exposure to [[emulsion|emulsifying agents]] due to human [[pollution]]. Feathers can become waterlogged and birds may sink. It is also very difficult to clean and rescue birds whose feathers have been fouled by [[oil spill]]s.
[[Bristle]]s are stiff, tapering feathers with a large rachis but few barbs. '''Rictal bristles''' are bristles found around the eyes and bill. They may serve a similar purpose to [[eyelash]]es and [[vibrissae]] in [[mammal]]s. It has been suggested that they may aid insectivorous birds in prey capture or that it may have sensory functions, however there is no clear evidence.<ref>Lederer R. J. (1972) The role of avian rictal bristles. Wilson. Bull. 84, 193-97 [http://elibrary.unm.edu/sora/Wilson/v084n02/p0193-p0197.pdf pdf]</ref> In one study, Willow Flycatchers (''Empidonax traillii'') and they were found to catch insects equally well before and after removal of the rictal bristles.<ref>Conover, M. R., and D. E. Miller (1980) Rictal bristle function in willow flycatcher. Condor 82:469-471.</ref>
[[Image:Pterylae.svg|thumb|Feather tracts or pterylae and their naming]]
Feathers are not uniformly distributed on the skin of the bird except in the [[Penguin]]. In most birds the feathers grow from specific tracts of skin called pterylae while there are regions which are free of feathers called apterylae. The arrangement of these feather tracts, pterylosis, varies across bird families.
==Evolution==
Feathers most likely originated as a filamentous insulation structure, or possibly as markers for mating, with flight emerging only as a secondary purpose. It has been thought that feathers evolved from the [[scale (zoology)|scales]] of [[reptile]]s, but recent research suggests that while there is a definite relationship between these structures, it remains uncertain of the exact process. (see ''Quarterly Review of Biology'' 77:3 (September 2002): 261-95). In experiments where a virus was used to reduce the levels of certain proteins in chicken embryos, the chickens retained webbed feet, and the [[scute]]s developed into feathers. The scales, however, did not develop into feathers, and the research suggests that feathers did not evolve from reptilian scales. <ref>[http://www.dinosauria.com/jdp/archie/scutes.htm Feathers, scutes and the origin of birds<!-- Bot generated title -->]</ref>
===Feathered dinosaurs===
{{Main|Feathered dinosaurs}}
Several [[feathered dinosaurs|dinosaurs]] have been discovered with feathers on their limbs that would not have functioned for flight. One theory is that feathers originally developed on dinosaurs as a means of [[Thermal insulation|insulation]]; those small dinosaurs that then grew longer feathers may have found them helpful in gliding, which would have begun the evolutionary process that resulted in some proto-birds like ''[[Archaeopteryx]]'' and ''[[Microraptor]] zhaoianus''. Other dinosaurs discovered with feathers include ''[[Pedopenna]] daohugouensis'', ''[[Sinosauropteryx]]'', and ''[[Dilong paradoxus]]'', a [[tyrannosauroid]] which is 60 to 70 million years older than ''[[Tyrannosaurus|Tyrannosaurus rex]]''. Currently the question is not whether birds are dinosaurs, but whether they are [[deinonychosauria]]ns or are [[dromaeosaurid]]s. It has been suggested that ''Pedopenna'' is older than ''Archaeopteryx'', however, their age remains doubted by some experts.
==Human uses==
[[Image:Shaft of Indian Peacock tail feather.jpg|200px|thumb|right|Shaft of Indian Peacock tail feather]]
Feathers have a number of utilitarian and cultural and religious uses.
===Utilitarian functions===
Feathers are both soft and excellent at trapping [[heat]]; thus, they are sometimes used in high-class [[bedding]], especially [[pillow]]s, [[blanket]]s, and [[mattress]]es. They are also used as filling for winter [[clothing]], such as quilted [[coat]]s and [[sleeping bag]]s; [[goose]] down especially has great ''loft'', the ability to expand from a compressed, stored state to trap large amounts of compartmentalized, insulating air. Bird feathers have long been used for [[fletching]] [[arrow (weapon)|arrow]]s and in the past were used for ink pens. Colorful feathers such as those belonging to [[pheasant]]s have been used to decorate [[fishing lure]]s and [[hat]]s. During the 18th, 19th, and even 20th Centuries a booming international trade in plumes, to satisfy market demand in North America and Europe for extravagant [[headgear|head-dresses]] as adornment for fashionable women, caused so much destruction (for example, to [[egret]] breeding colonies) that a major campaign against it by conservationists caused the fashion to change and the market to collapse.
Feathers of large birds (most often [[Goose|geese]]) have been and are used to make [[quill]] pens. The word '''pen''' itself is derived from the Latin ''penna'' for feather.<ref>The American Heritage Dictionary of the English Language, Fourth Edition. 2000. Houghton Mifflin Company. [http://209.10.134.179/61/93/P0159300.html]</ref> The French ''nom-de-plume'' for [[pen name]] has a similar origin.
===Cultural and religious uses===
[[Image:GuineaFeather.jpg|thumb|right|A feather from a [[Guinea fowl]].]]
[[Eagle]] feathers have great [[cultural]] and [[Spirituality|spiritual]] value to [[Native Americans in the United States|American Indians]] in the [[USA]] and [[First Nations]] peoples in [[Canada]] as religious objects. In the United States the [[religious]] use of [[eagle]] and [[hawk]] feathers are governed by the [[eagle feather law]] (50 CFR 22), a federal law limiting the possession of eagle feathers to certified and enrolled members of federally recognized Native American tribes.
Various birds and their plumages serve as cultural icons throughout the world, from the hawk in ancient Egypt to the bald eagle and the turkey in the United States. In [[Greek mythology]], Daedelus the inventor and [[Icarus (mythology)|Icarus]] tried to escape his prison by attaching feathered wings to his shoulders with wax, which was melted by the Sun.
==See also==
* [[Flight feather]]
* [[Down feather]]
* [[Pinioning]]
* [[Eagle feather law]]
==References==
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==External links==
{{commons|Feather|Feather}}
* McGraw, K. J. 2005. [http://www.public.asu.edu/~kjmcgraw/pubs/ABK2005.pdf Polly want a pigment? Cracking the chemical code to red coloration in parrots.] Australian Birdkeeper Magazine 18:608-611.
* DeMeo, Antonia M. ''Access to Eagles and Eagle Parts: Environmental Protection v. Native American Free Exercise of Religion'' (1995) [http://www.animallaw.info/articles/ar22hstclq771.htm]
* Electronic Code of Federal Regulations (e-CFR), ''Title 50: Wildlife and Fisheries PART 22—EAGLE PERMITS'' [http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&tpl=/ecfrbrowse/Title50/50cfr22_main_02.tpl]
* Stokes, DaShanne. (In Press) [http://www.geocities.com/eaglefeatherlaw/stokes.article.html ''Legalized Segregation and the Denial of Religious Freedom'']
* U.S. v. Thirty Eight Golden Eagles (1986) [http://www.animallaw.info/cases/caus649fsupp269.htm]
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