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[[Image:Types de plumes. - Larousse pour tous, -1907-1910-.jpg|thumb|Feather variations]]

{{Otheruses}}
'''Feathers''' are one of the [[epidermal growth]]s that form the distinctive outer covering, or [[plumage]], on [[bird]]s. They are considered the most complex [[integumentary]] structures found in vertebrates.<ref name=Prum2002>{{cite journal|author=Prum, Richard O. & AH Brush|year=2002|title=The evolutionary origin and diversification of feathers|journal=The Quarterly Review of Biology|volume=77|issue=3|pages=261–295|doi=10.1086/341993|pmid=12365352}}</ref><ref name="Prum2003"> Prum, R.O., & Brush, A.H. (March 2003). "Which Came First, the Feather or the Bird?" ''Scientific American'', vol.288, no.3, pp. 84-93</ref> They are among the outstanding characteristics that distinguish the extant [[Aves]] from other living groups. Feathers have also been noticed in [[Theropoda]] which have been termed [[feathered dinosaurs]]. However, there are also some scientists who disagree with the interpretation of feathered dinosaurs<ref name="Feduccia et al. 2005"> Feduccia, A., T. Lingham-Soliar & J.R. Hinchliffe (2005). "Do Feathered Dinosaurs Exist? Testing the Hypothesis on Neontological and Paleontological Evidence" ''Journal of Morphology'', vol.266, pp. 125-166</ref>, pointing out instead that birds and some theropods are only convergently similar. Although feathers cover most parts of the body of birds, they arise only from certain well-defined tracts on the skin. They aid in flight, thermal insulation, waterproofing and coloration that helps in communication and [[crypsis|protection]].<ref name=pettingill>{{cite book|author=Pettingill, OS Jr.|year=1970|title=Ornithology in Laboratory and Field. Fourth edition|publisher=Burgess Publishing Company|isbn=808716093|pages=29–58}}</ref>

==Structure and characteristics==
[[Image:Parts of feather modified.jpg|thumb|'''Parts of a feather:'''<br/>1. Vane<br/>2. Rachis<br/>3. Barb<br/>4. Afterfeather<br/>5. Hollow shaft, calamus]]
[[Image:Parrot-feather.jpg|thumb|Featherstructure of a [[Blue-and-yellow Macaw]]]]
Feathers are among the most complex [[Integumentary system|integument]]ary [[appendages]] found in [[Vertebrata|vertebrates]] and are formed in tiny follicles 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]].<ref>{{cite journal|journal=Biophys J.|year=1961|volume=1|issue=6|pages=489–515|title=Studies on the Structure of Feather Keratin II. A β-Helix Model for the Structure of Feather Keratin|author=R. Schor and S. Krimm|pmcid=PMC1366335|doi=10.1016/S0006-3495(61)86904-X|pmid=19431311|pmc=1366335}}</ref><ref>{{Cite journal|title=The Structure of Feather Rachis keratin|author=Linus Pauling and Robert B. Corey|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=37|issue=5|year=1951|pages=256–261|doi=10.1073/pnas.37.5.256|pmid=14834148|pmc=1063351}}</ref> The exact signals that induce the growth of feathers on the skin are not known but it has been found that the transcription factor cDermo-1 induces the growth of feathers on skin and scales on the leg.<ref>{{cite journal|author=Hornik, C., Krishan, K., Yusuf, F., Scaal, M., & Brand-Saberi, B.|year=2005|title=cDermo-1 misexpression induces dense dermis, feathers, and scales|journal=Developmental Biology|volume=277|issue=1|pages=42–50|doi=10.1016/j.ydbio.2004.08.050|pmid=15572138}}</ref>
[[Image:FeatherLocking.png|thumb|left|Feather microstructure showing interlocking]]
===Classification===
{{see also|Flight feather}}
There are two basic types of feather: '''vaned feathers''' which cover the exterior of the body, and '''[[down feather]]s''' which are underneath the vaned feathers. The [[pennaceous feather]]s are vaned feathers. Also called '''contour feathers''', pennaceous feathers arise from tracts and cover the whole body. A third rarer type of feathers, '''filoplumes''', is hairlike and (if present in a bird) grows along the fluffy down feathers. In some passerines filoplumes arise exposed beyond the contour feathers on the neck.<ref name=Prum2002/> The remiges, or [[flight feather]]s of the wing, and rectrices, the flight feathers of the tail are the most important feathers for flight. 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]]. The basal part of the calamus is without vanes. This part is embedded within the skin follicle and has an opening at the base (proximal umbilicus) and a small opening on the side (distal umbilicus).<ref name=atlas>{{cite book|title=A color atlas of avian anatomy|author=McLelland, J.|publisher=W.B. Saunders Co.|year=1991}}</ref>

Hatchling birds of some species have a special kind of natal down (neossoptiles) and these are pushed out when the normal feathers (teleoptiles) emerge.<ref name=Prum2002 />

Flight feathers are stiffened so as to work against the air in the downstroke but yield in other directions. It is noted that the pattern of orientation of β-keratin fibers in the feathers of flying birds differs from that in flightless birds. The fibers are better aligned in the middle of the feather and less aligned towards the tips.<ref>{{cite journal|author=Cameron, G., Wess, T., & Bonser, R.|year=2003|title=Young’s modulus varies with differential orientation of keratin in feathers|journal=Journal of Structural Biology|volume=143|issue=2|pages=118|doi=10.1016/S1047-8477(03)00142-4|pmid=12972348}}</ref><ref>{{cite journal|author=Bonser, R., Saker, L., & Jeronimidis, G.|year=2004|title=Toughness anisotropy in feather keratin|journal=Journal of Materials Science|volume=39|issue=8|pages=2895–2896|doi=10.1023/B:JMSC.0000021474.75864.ff}}</ref>

===Functions===
Feathers insulate birds from water and cold temperatures. They may also be plucked to line the nest and provide insulation to the eggs and young. The individual feathers in the wings and tail play important roles in controlling flight. 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. In some cases there are differences in the UV reflectivity of feathers across sexes even though no differences in color are noted in the visible range.<ref>{{cite journal|title=The Ubiquity of Avian Ultraviolet Plumage Reflectance|author=Muir D. Eaton and Scott M. Lanyon|journal=Proceedings: Biological Sciences|volume=270|issue=1525|year=2003|pages=1721–1726|doi=10.1098/rspb.2003.2431|pmid=12965000|pmc=1691429}}</ref> The wing feathers of male [[Club-winged Manakin]]s ''Machaeropterus deliciosus'' have special structures that are used to produce sounds by [[stridulation]].<ref>{{cite journal|title=Courting Bird Sings with Stridulating Wing Feathers|author=Bostwick, Kimberly S. and Richard O. Prum|year=2005|journal=Science|volume=309|issue=5735|pages=736|doi=10.1126/science.1111701|pmid=16051789}}</ref>
[[Image:GuineaFeather.jpg|thumb|left|A contour feather from a [[Guinea fowl]].]]
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. The feathers of cormorants soak up water and help in reducing buoyancy and thereby allowing the birds to swim submerged.<ref>{{cite journal|author=Ribak, G., Weihs, D. and Arad, Z.|year=2005|title=Water retention in the plumage of diving great cormorants ''Phalacrocorax carbo sinensis''|journal=J. Avian Biol.|volume=36|pages=89–95|doi=10.1111/j.0908-8857.2005.03499.x}}</ref>
[[Image:BarbetRictalBristle.jpg|thumb|Rictal bristles of a [[White-cheeked Barbet]]]]
[[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>

[[Grebe]]s are peculiar in their habit of ingesting their own feathers and also feeding them to their young. Observations on the diet and feather eating frequency suggest that ingesting feathers particularly down from their flanks aids in forming easily ejectable pellets along with their diet of fish.<ref>{{cite journal|title=Feather eating in Great Crested Grebes ''Podiceps cristatus'': a unique solution to the problems of debris and gastric parasites in fish-eating birds|author=Piersma, T & M R van Eerden|journal=Ibis|volume=131|issue=4|pages=477–486|year=1989|doi=10.1111/j.1474-919X.1989.tb04784.x}}</ref>

===Distribution===
[[Image:Pterylae.svg|thumb|Feather tracts or pterylae and their naming]]
Contour feathers are not uniformly distributed on the skin of the bird except in some groups such as the [[Penguin]]s, ratites and screamers.<ref>{{cite journal|title=A Study of the Pterylosis and Pneumaticity of the Screamer|author=Demay, Ida S.|journal=The Condor|volume=42|issue=2|year=1940|pages=112–118|doi=10.2307/1364475}}</ref> In most birds the feathers grow from specific tracts of skin called pterylae while there are regions which are free of feathers called apterylae. Filoplumes and down may arise from the apteriae, regions between the pterylae. The arrangement of these feather tracts, pterylosis or pterylography, varies across bird families and has been used in the past as a means for determining the evolutionary relationships of bird families.<ref>{{cite journal|journal=Journal of Ornithology|title=Do nine-primaried passerines have nine or ten primary feathers? The evolution of a concept|volume=146|issue=2|pages=121–126|year=2005|author=K. Susanna S. Hall|doi=10.1007/s10336-004-0070-5}}</ref><ref>{{cite journal|author=Pycraft, W. P.|year=1895|title=On the pterylography of the hoatzin (''Opisthocomus cristatus'')|journal=Ibis|volume=37|pages=345–373|doi=10.1111/j.1474-919X.1895.tb06744.x}}</ref>

===Coloration===
The colors of feathers are produced by the presence of pigments such as [[melanin]]s (browns, blacks, greys), [[carotenoid]]s (reds, yellows, orange), [[psittacofulvin]]s (unique red pigments found in some parrots)<ref>{{cite journal|journal=Biology Letters|title=Distribution of unique red feather pigments in parrots|volume=1|issue=1|pages=38–43|year=2005|author=McGraw KH & MC Nogare|doi=10.1098/rsbl.2004.0269|pmid=17148123|pmc=1629064}}</ref> and [[porphyrin]]s (such as the green turacoverdin of Turacos) or more often by feather structure. Structural coloration is involved in the production of most greens, blues, iridescent colors, ultraviolet reflectance and in the enhancement of pigmentary colors.<ref name=pettingill/><ref>{{cite journal|author=Hausmann, F., Arnold, K.E., Marshall, N.J. & Owens, I.P.F.|year=2003|title=Ultraviolet signals in birds are special|journal=Proc. R. Soc. B|volume= 270|pages= 61–67|doi=10.1098/rspb.2002.2200|pmid=12590772|issue=1510|pmc=1691211}}</ref><ref>{{cite journal|title= Carotenoids need structural colours to shine|author=Matthew D Shawkey and Geoffrey E Hill|journal= Biol Lett.|year=2005 |volume =1|issue= 2 |pages=121–124|doi=10.1098/rsbl.2004.0289|url=http://nature.berkeley.edu/%7Emshawkey/9.pdf|format=PDF|pmid= 17148144|pmc= 1626226}}</ref> Structural iridescence in feathers has been reported in fossil feathers dating back 40 million years.<ref>{{cite journal|last=Vinther|first=Jakob |coauthors=Derek E. G. Briggs; Julia Clarke; Gerald Mayr; Richard O. Prum|date=2009|title=Structural coloration in a fossil feather|journal=Biology Letters| doi = 10.1098/rsbl.2009.0524|pmid=19710052 }}</ref>

The blues and greens of many parrots are produced by constructive interference of light reflecting from different layers of the structures in feathers in addition to the yellow carotenoid pigments. Melanin is often involved in the absorption of some of the light in these feathers. The specific feather structure involved is sometimes called the Dyck texture.<ref>{{cite journal|author=Dyck J.|title= Structure and spectral reflectance of green and blue feathers of the Lovebird (''Agapornis roseicollis'')|journal=Biol. Skr.|year=1971|volume=18|pages=1–67}}</ref><ref>{{cite journal|journal=The Auk|volume=121|issue=3|pages=652–655|year=2005|title=Feathers at a fine scale|author=Shawkey MD & G E Hill|url=http://nature.berkeley.edu/%7Emshawkey/6.pdf|format=PDF|doi=10.1642/0004-8038(2004)121[0652:FAAFS]2.0.CO;2}}</ref>
[[Image:BWfeather.jpg|thumb|130px|A feather with no pigment]]
[[Albinism in birds|Albinism]] is caused by the 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>{{cite journal|author=Delhey K, A. Peters, and B. Kempenaers|year=2007|title=Cosmetic coloration in birds: occurrence, function and evolution|journal=Am. Nat.|volume=169|pages=S145–158|url=http://www.orn.mpg.de/documents/peters/Delhey_AmNat2007_copy.pdf|format=PDF|doi=10.1086/510095|pmid=19426089}}</ref> but studies have failed to find evidence.<ref>{{cite journal|author=Delhey, K., A. Peters, PHW Biedermann & B Kempenaers|year=2008|title=Optical properties of the uropygial gland secretion: no evidence for UV cosmetics in birds|journal=Naturwissenschaften|doi=10.1007/s00114-008-0406-8|volume=95|pages=939|pmid=18560743|issue=10}}</ref> Uropygial oil secretion may also have an inhibitory effect on feather bacteria.<ref>{{cite journal|author=Shawkey, M.D., S.R. Pillai, and G.E. Hill|year=2003|title=Chemical warfare? Effects of uropygial oil on feather-degrading bacteria|journal=Journal of Avian Biology|volume=34|pages=345–349|url=http://nature.berkeley.edu/~mshawkey/2.pdf|format=PDF|doi=10.1111/j.0908-8857.2003.03193.x}}</ref>

A bird's feathers undergo wear and tear and are replaced periodically during its life through [[molt]]ing. New feathers are formed through the same follicle from which the old ones were fledged. The presence of melanin in feathers increases their resistance to abrasion.<ref>{{cite journal|author=Bonser, R. H. C.|year=1995|title=Melanin and the abrasion resistance of feathers|journal=Condor|volume=97|pages=590–591|doi=10.2307/1369048|issue=2}}</ref> One study notes that melanin based feathers were observed to degrade more quickly under bacterial action, even compared to unpigmented feathers from the same species, than those unpigmented or with carotenoid pigments.<ref>{{cite journal|journal=Ardeola|volume=51|issue=2|year=2004|pages=375–383|title=The evolution of bird plumage colouration: A role for feather-degrading bacteria?|author=Grande JM, Negro JJ & MJ Torres|url=http://www.ardeola.org/files/Ardeola_51(2)_375-383.pdf|format=PDF}}</ref> However, another study the same year compared the action of bacteria on pigmentations of two song sparrow species and observed that the darker pigmented feathers were more resistant and they cited other research also published in 2004 that stated increased melanin proviided greater resistance. They observed that the greater resistance of the darker birds confirmed [[Gloger's rule]].<ref>{{cite journal|author=Burtt, Edward H. Jr. & Ichida, Jann M.|year=2004|title=Gloger's Rule, feather-degrading bacteria, and color variation among Song Sparrows|journal=Condor|volume=106|issue=3|pages=681–686|doi=10.1650/7383|url=http://www.public.asu.edu/~kjmcgraw/pubs/Condor04b.pdf|format=PDF}}</ref> The evolution of coloration is based on sexual selection and it has been suggested that carotenoid based pigments may have evolved since they are likely to be more honest signals of fitness since they are derived from special diets.<ref>{{cite journal|author=Badyaev AV & Hill GE|year=2000|title=Evolution of sexual dichromatism: contribution of carotenoid versus melanin-based colouration|journal=Biological Journal of the Linnean Society|volume=69|pages=153–172|doi=10.1111/j.1095-8312.2000.tb01196.x}}</ref>

==Parasites==
The feather surface is the home for some ectoparasites, notably feather lice ([[Phthiraptera]]) and feather mites. Feather lice typically live on a single host and can move only from parents to chicks or mating birds and occasionally by [[phoresy]]. This life history has resulted in most of the species being specific to the host and coevolving with the host, making them of interest in phylogenetic studies.<ref>{{cite journal|author=Toon, A., & Hughes, J.|year=2008|title=Are lice good proxies for host history? A comparative analysis of the Australian magpie, ''Gymnorhina tibicen'', and two species of feather louse|journal=Heredity|volume=101|issue=2|pages=127–135|doi=10.1038/hdy.2008.37|pmid=18461081}}</ref>

[[Feather holes]] are chewing traces of lice (most probably ''Brueelia'' spp. lice) on the wing and tail feathers. They were described on [[barn swallow]]s, and because of easy countability, many evolutionary, ecological, and behavioral publications use them to quantify the intensity of infestation.

Interestingly, parasitic cuckoos which grow up in the nests of other species also have host specific feather lice and these seem to be transmitted only after they leave the host nest.<ref>{{cite journal|author=Brooke, M. de L. and Hiroshi Nakamura|year=1998|title=The acquisition of host-specific feather lice by common cuckoos (''Cuculus canorus'')|journal=Journal of Zoology|volume=244|pages=167–173|doi=10.1017/S0952836998002027}}</ref>

Birds maintain their feather condition by bathing in water, dust bathing and preening. A peculiar behavior of birds, [[anting (bird activity)|anting]], where ants are introduced into the plumage was suggested to help in reducing parasites but no supporting evidence has been found.<ref>{{cite journal|author=Revis, Hannah C., and Deborah A. Waller|year=2004|title=Bactericidal and fungicidal activity of ant chemicals on feather parasites: an evaluation of anting behavior as a method of self-medication in songbirds| journal=Auk|volume=121|issue=4|pages=1262–1268|doi=10.1642/0004-8038(2004)121[1262:BAFAOA]2.0.CO;2}}</ref>

==Human usage==
[[Image:Shaft of Indian Peacock tail feather.jpg|thumb|right|Shaft of Indian Peacock tail feather]]
Feathers have a number of utilitarian, 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]] and [[eider]] down have great ''loft'', the ability to expand from a compressed, stored state to trap large amounts of compartmentalized, insulating air.<ref>{{cite journal|journal=Journal of Materials Science Letter|title=The structural mechanical properties of down feathers and biomimicking natural insulation materials|volume=18|issue=21|pages=1769–1770|year=1999|author=Bonser, R.H.C. & Dawson, C.|doi=10.1023/A:1006631328233}}</ref>

Bird feathers have long been used for [[fletching]] [[arrow (weapon)|arrow]]s. Colorful feathers such as those belonging to [[pheasant]]s have been used to decorate [[fishing lure]]s.

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.

Feathers are also valuable in aiding the identification of species in forensic studies, particularly in bird strikes to aircraft. The ratios of hydrogen isotopes in feathers help in determining the geographic origins of birds.<ref>{{cite journal|journal=Oecologia|title=Global application of stable hydrogen and oxygen isotopes to wildlife forensics|volume=143|issue=3|pages=337–348|doi=10.1007/s00442-004-1813-y|year=2005|pmid=15726429|author1=Bowen, Gabriel J|author2=Wassenaar, Leonard I|author3=Hobson, Keith A}}</ref> Feathers may also be useful in the non-destructive sampling of pollutants.<ref>{{cite journal|author=Jaspers, V., Voorspoels, S., Covaci, A., Lepoint, G., & Eens, M.|year=2007|title=Evaluation of the usefulness of bird feathers as a non-destructive biomonitoring tool for organic pollutants: A comparative and meta-analytical approach|journal=Environment International|volume=33|issue=3|pages=328–337|doi=10.1016/j.envint.2006.11.011|pmid=17198730}}</ref>

The poultry industry produces a large amount of feathers as waste, and like other forms of keratin, these are slow in their decomposition. Feather waste has been used in a number of industrial applications as a medium for culturing microbes,<ref>{{cite journal|title=Use of feather-based culture media for the production of mosquitocidal bacteria|doi=10.1016/j.biocontrol.2007.04.019|journal=Biological Control|volume=43|issue=1|pages=49–55|author=Subbiah Poopathi, S. Abidha|year=2007}}</ref> biodegradeable polymers,<ref>{{cite journal|author=Schmidt, W.F., Barone, J.R.|year=2004|title=New uses for chicken feathers keratin fiber. Poultry Waste Management Symposium Proceedings|pages=99–101}}</ref> and production of enzymes.<ref>{{cite journal|journal=Food and Bioprocess Technology|title=Use of Poultry Byproduct for Production of Keratinolytic Enzymes|volume=1|issue=3|pages=301–305|year=2008|doi=10.1007/s11947-008-0091-9|author1=Casarin, Franciani|author2=Brandelli, Florencia Cladera-Olivera Adriano}}</ref> Feather proteins have been tried as an adhesive for wood board.<ref>{{cite journal|author=Jiang, Z., Qin, D., Hse, C., Kuo, M., Luo, Z., Wang, G., et al.|year=2008|title=Preliminary Study on Chicken Feather Protein-Based Wood Adhesives|journal=Journal of Wood Chemistry & Technology|volume=28|issue=3|pages=240–246|doi=10.1080/02773810802347073}}</ref>

===In religion and culture===
[[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]], 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 (bird)]] 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.

In South America, brews made from the feathers of Condors are used in traditional medications.<ref>{{cite journal|author=Steve Froemming|title=Traditional use of the Andean flicker (''Colaptes rupicola'') as a galactagogue in the Peruvian Andes|journal=Journal of Ethnobiology and Ethnomedicine| year=2006|volume=2|pages=23 |doi=10.1186/1746-4269-2-23|pmid=16677398|pmc=1484469}}</ref> In India, feathers of the [[Indian Peacock]] have been used in traditional medicine for snakebite, infertility and coughs.<ref>{{cite journal|author=Murari, S.K., Frey, F.J., Frey, B.M., Gowda, T.V., Vishwanath, B.S.|year=2005|title=Use of ''Pavo cristatus'' feather extract for the better management of snakebites: Neutralization of inflammatory reactions|journal=Journal of Ethnopharmacology|volume=99|issue=2|pages=229–237|doi=10.1016/j.jep.2005.02.027|pmid=15894132}}</ref><ref>{{cite journal|title=Traditional knowledge on zootherapeutic uses by the Saharia tribe of Rajasthan, India|author=Mahawar, MM & DP Jaroli|journal=J Ethnobiol Ethnomedicine|year=2007|volume=3|pages=25|doi=10.1186/1746-4269-3-25|pmid=17547781|pmc=1892771}}</ref>

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 led to the [[Lacey Act]] and caused the fashion to change and the market to finally collapse. [[Frank Chapman]] noted in 1886 that as many as 40 species of birds were used in about three-fourths of the 700 ladies' hats that he observed in New York City.<ref>Doughty, Robin W. 197. Feather Fashions and Bird Preservation, A Study in Nature Protection. University of California Press.</ref><ref>Ehrlich, Paul R.; Dobkin. David S.; Wheye. Darryl (1988) [http://www.stanford.edu/group/stanfordbirds/text/essays/Plume_Trade.html Plume Trade] Stanford University</ref><ref>[http://americanhistory.si.edu/feather/ftfa.htm Feather trade] Smithsonian Institution</ref>

==Evolution==
{{main|Origin of avian flight}}
[[File:Archaeopteryx (Feather).jpg|thumb|right|upright|Fossil feather of [[Archaeopteryx]] ]]
The functional view on the evolution of feathers has traditionally focussed on insulation, flight and display. Discoveries of non-flying Late Cretaceous feathered dinosaurs in China however suggest that flight could not have been the original primary function.<ref name=sumida>{{cite journal|author=Sumida, SS & CA Brochu|year=2000|title=Phylogenetic context for the origin of feathers|doi=10.1093/icb/40.4.486|journal=American Zoologist|volume=40|issue=4|pages=486–503|url=http://icb.oxfordjournals.org/cgi/content/abstract/40/4/486}}</ref> While feathers have been suggested as having evolved from reptilian [[scale (zoology)|scales]], there are numerous objections, and more recent explanations have arisen from the paradigm of [[evolutionary developmental biology]].<ref name=Prum2003/> Theories of the scale-based origins of feathers suggest that the planar scale structure was modified for their development into feathers by splitting to form the webbing; however, the developmental process involves a tubular structure arising from a follicle and the tube splitting longitudinally to form the webbing.<ref name=Prum2002/><ref name=Prum2003/> The number of feathers per unit area of skin is higher in smaller birds than in larger birds, and this trend indicates their important role in thermal insulation, since smaller birds lose more heat due to the relatively larger surface area in proportion to their body weight.<ref name=pettingill/> The coloration of feathers is believed to be primarily evolved in response to [[sexual selection]]. In many cases the physiological condition of the birds (especially males) is indicated by the quality of their feathers and this is used (by the females) in [[mate choice]].<ref>{{cite journal|author=Saino, Nicola, and Riccardo Stradi|year=1999|title=Carotenoid Plasma Concentration, Immune Profile, and Plumage Ornamentation of Male Barn Swallows|journal=American Naturalist|volume=154|issue=4|pages=441|doi=10.1086/303246|pmid=10523490}}</ref><ref>{{cite journal|author=Endler, John A., David A. Westcott, Joah R. Madden, Tim Robson, and Patrick Phillips|year=2005|title=Animal visual systems and the evolution of color patterns: Sensory processing illumiates signal evolution|journal=Evolution|volume=59|issue=8|pages=1795–1818|pmid=16329248}}</ref>

===Feathered dinosaurs===
{{Main|Feathered dinosaurs}}
[[File:Archaeopteryx lithographica (Berlin specimen).jpg|thumb|right|upright|Archaeopteryx lithographica (Berlin specimen)]]
Several non-avian [[feathered dinosaurs|dinosaurs]] had feathers on their limbs that would not have functioned for flight.<ref name=Prum2003/> One theory is that feathers originally evolved on dinosaurs as a result of [[Thermal insulation|insulation]] properties; those small dinosaurs that then grew longer feathers may have found them helpful in gliding leading to the evolution of proto-birds like ''[[Archaeopteryx]]'' and ''[[Microraptor]] zhaoianus''. However, Prum's model of the origin of feathers present many difficulties. First of all, dinosaurs were probably ectotherms<ref name=cold>{{cite book|title=A Cold look at the warm-blooded dinosaurs|author=Thomas, Roger D. K. and Everett C. Olson, ed.|publisher=Westview Press for the American Association for the Advancement of Science|year=1980}}</ref>, so they did not need insulation. Second, feathers are complex structures and they would be overkill if they evolved originally as insulation. A third difficulty is that flight almost certainly evolved from the tree down, but Prum's model would have necessitated flight having evolved from the ground up. ''[[Sinosauropteryx]]'' had short fibres that were most likely collagen fibers. Feathers are seen in ''[[Protarchaeopteryx]]'' and ''[[Caudipteryx]]'', which are probably two flightless birds, not dinosaurs.<ref name=sumida/> Other dinosaurs that had feathers or protofeathers include ''[[Pedopenna]] daohugouensis'',
<ref>{{cite journal|journal= Naturwissenschaften|title=A new maniraptoran dinosaur from China with long feathers on the metatarsus|volume=92|issue=4|pages=173–177|author=Xu, Xing & Fucheng Zhang|doi=10.1007/s00114-004-0604-y|year= 2005|pmid= 15685441}}</ref> and ''[[Dilong paradoxus]]'', a [[tyrannosauroid]] which is 60 to 70 million years older than ''[[Tyrannosaurus|Tyrannosaurus rex]]''.<ref>{{cite journal|author=Xu, Xing|title=Feathered dinosaurs from China and the evolution of major avian characters|journal=Integrative Zoology|volume=1|issue=1|pages=4–11|year=2006|doi=10.1111/j.1749-4877.2006.00004.x}}</ref>

The majority of dinosaurs known to have had feathers or protofeathers are [[saurischian]]s, however featherlike "filamentous integumentary structures" are also known from the [[ornithischian]]s ''[[Tianyulong]]'' and ''[[Psittacosaurus]]''. The exact nature of these structures is still under study. Since Ornithischians are only distantly related to birds, the presence of feathers on their skins would make no sense whatsoever. The most likely explanation is that these "filamentous integumentary structures" are collagen fibers that are present in the skin of all vertebrates. The animal that is most likely to have protofeathers may be the late Triassic ''Longisquama insignis''. <ref>{{cite journal|author=Jones, T.D., Ruben, J.A., Martin, L.D., Kurochkin, E., Feduccia, A., Maderson, P.F.A., Hillenius, W.J., Geist, N.R., Alifanov, V.|title=Nonavian Feathers in a Late Triassic Archosaur|journal=Science|volume=288|issue=5474|pages=2202-2205|year=2000}}</ref>

Since the 1990s, dozens of feathered dinosaurs have been discovered in the clade [[Maniraptora]], which includes the clade Avialae and the recent common ancestors of birds, [[Oviraptorosauria]] and [[Deinonychosauria]]. In 1998, the discovery of a feathered oviraptorosaurian, ''Caudipteryx zoui'', challenged the notion that feathers were an exclusive structure of Avialae.<ref>{{cite journal |author=Ji, Q., P. J. Currie, M. A. Norell, and S. A. Ji |title=Two feathered dinosaurs from northeastern China |journal=Nature |volume=393 |year=1998 |page=753-761 }}</ref> Buried in the Yixian Formation in Liaoning, China, ''C. zoui'' lived during the Early Cretaceous Period. Present on the forelimbs and tails, their integumentary structure has been accepted as pennaceous vaned feathers based on the rachis and herringbone pattern of the barbs. In the clade Deinonychosauria, the continued divergence of feathers is also apparent in the families [[Troodontidae]] and [[Dromaeosauridae]]. Branched feathers with ranchis, barbs, and barbules were discovered in many members including ''Sinornithosaurus millenii'', a dromaeosaurid found in the Yixian formation (124.6 MYA).<ref>{{cite journal |author=Xu, X., H. H. Zhou, and R. O. Prum |title=Branched integumental structures in Sinornithosaurus and the origin of feathers |journal=Nature |volume=410 |year=2001 |page=200-204 }}</ref>

Previously, a temporal paradox existed in the evolution of feathers - theropods with highly derived bird-like characteristics occurred at a later time than ''[[Archaeopteryx]]'', suggesting that the descendants of birds arose before the ancestor. However, this paradox was resolved in 2009 with the discovery of ''Anchiornis huxleyi'', found in the Late Jurassic Tiaojishan Formation (160 MYA) in western Liaoning. <ref>{{cite journal |author=Hu, D. Y., L. H. Hou, L. J. Zhang, and X. Xu |title=A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus |journal=Nature |volume=461 |year=2009 |page=640-643 |doi=10.1038/nature08322}}</ref> <ref>{{cite journal |author=Xu, X., Q. Zhao, M. Norell, C. Sullivan, D. Hone, G. Erickson, X. L. Wang et al. |title=A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin |journal=Chinese Science Bulletin |volume=54 |year=2009 |page=430-435 |doi=10.1007/s11434-009-0009-6}}</ref> By predating ''Archaeopteryx'', ''Anchornis'' proves the existence of a modernly feathered theropod ancestor, providing insight into the dinosaur-bird transition. The specimen shows distribution of large pennaceous feathers on the forelimbs and tail, implying that pennaceous feathers spread to the rest of the body at a earlier stage in theropod evolution. <ref>{{cite journal |author=Witmer, L. M. |title=Feathered dinosaurs in a tangle |journal=Nature |volume=461 |year=2009 |page=601-602 |doi=10.1038/461601a}}</ref>

===Evolutionary stages===
[[Image:Feather stages diagram.svg|thumb|right|Diagram illustrating stages of evolution]]
Several studies of feather development in the embryos of modern birds, coupled with the distribution of feather types among various prehistoric bird precursors, have allowed scientists to attempt a reconstruction of the sequence in which feathers first evolved and developed into the types found on modern birds.

Feather evolution can be broken down into the following stages:<ref name="xu&guo2009">Xu, X. and Guo, Y. (2009). "The origin and early evolution of feathers: insights from recent paleontological and neontological data." ''Vertebrata PalAsiatica'', '''47'''(4): 311-329.</ref>
# Single filament
# Multiple filaments joined at their base
# Multiple filaments joined at their base to a central filament
# Multiple filaments along the length of a central filament
# Multiple filaments arising from the edge of a membranous structure
# Pennaceous feather with vane of barbs and barbules and central rachis
# Pennaceous feather with an asymmetrical rachis
# Undifferentiated vane with central rachis

The following simplified diagram of dinosaur relationships follows these results, and shows the likely distribution of plumaceous (downy) and pennaceous (vaned) feathers among dinosaurs and prehistoric birds.<ref name="xu&guo2009"/> The numbers accompanying each name refer to the presence of specific feather stages. Note that 's' indicates the known presence of scales on the body.

{{clade| style=font-size:80%;line-height:70%
|label1=[[Dinosauria]]
|1={{clade
|label1=[[Ornithischia]]
|1={{clade
|1=[[Heterodontosauridae]] (1)
|2={{clade
|1=[[Thyreophora]] (s)
|2={{clade
|1=[[Ornithopoda]] (s)
|2={{clade
|1=[[Psittacosauridae]] (s, 1)
|2=[[Ceratopsidae]] (s)
}}
}}
}}
}}
|label2=[[Saurischia]]
|2={{clade
|1=[[Sauropodomorpha]] (s)
|2={{clade
|1={{clade
|1=''[[Aucasaurus]]'' (s)
|2=''[[Carnotaurus]]'' (s)
|3=''[[Ceratosaurus]]'' (s)
}}
|label2=[[Coelurosauria]]
|2={{clade
|1={{clade
|1=''[[Dilong]]'' (1)
|2=Other [[Tyrannosauroidea|tyrannosauroids]] (s)
}}
|2={{clade
|1={{clade
|1=''[[Juravenator]]'' (s)
|2=''[[Sinosauropteryx]]'' (1)
}}
|label2=[[Maniraptora]]
|2={{clade
|1=[[Therizinosaur]]ia (1, 2, 3)
|2={{clade
|1=[[Alvarezsauridae]] (1)
|2={{clade
|1=[[Oviraptorosauria]] (4, 6)
|label2=[[Paraves]]
|2={{clade
|1={{clade
|1=[[Troodontidae]] (2, 4, 6)
|2={{clade
|1=Other dromaeosaurids
|2={{clade
|1=''[[Sinornithosaurus]]'' (2, 3, 4)
|2=''[[Microraptor]]'' (2, 4, 6, 7)
}}
}}
}}
}}
|2={{clade
|1=[[Scansoriopterygidae]] (2, 5, 8)
|2={{clade
|1=[[Archaeopterygidae]] (4, 6, 7)
|2={{clade
|1=''[[Jeholornis]]'' (6, 7)
|2={{clade
|1=''[[Confuciusornis]]'' (4, 6, 7)
|2={{clade
|1=[[Enantiornithes]] (4, 6, 7, 8)
|2=[[Neornithes]] (4, 6, 7, 8)
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}

==See also==
* [[Pinioning]]

==References==
{{reflist|2}}

==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]
* U.S. v. Thirty Eight Golden Eagles (1986) [http://www.animallaw.info/cases/caus649fsupp269.htm]
*[http://www.rdg.ac.uk/biomim/personal/richard/keratin.htm Mechanical structure of feathers]
*[http://faculty.weber.edu/jcavitt/Lecture4.pdf Lecture notes on the avian integument]
*[http://www.lab.fws.gov/featheratlas U.S. National Fish and Wildlife Forensics Laboratory's Feather Atlas]

{{Birds}}
{{feather-tracts}}

[[Category:Feathers| ]]
[[Category:Animal products]]
[[Category:Bird anatomy]]

{{Link FA|sv}}
[[ar:ريش]]
[[ay:Phuyu]]
[[bs:Perje]]
[[br:Plu]]
[[bg:Перо]]
[[ca:Ploma]]
[[cs:Peří]]
[[da:Fjer]]
[[de:Feder]]
[[es:Pluma]]
[[eo:Plumo]]
[[fa:پر]]
[[fr:Plume]]
[[gd:Ite]]
[[gl:Pluma]]
[[hr:Perje]]
[[id:Bulu]]
[[it:Piuma]]
[[he:נוצה]]
[[jv:Wulu]]
[[lb:Fieder]]
[[lt:Plunksna]]
[[hu:Toll]]
[[ms:Bulu pelepah]]
[[nl:Veer (vogel)]]
[[ja:羽毛]]
[[no:Fjær]]
[[nn:Fjør]]
[[oc:Pluma]]
[[nds:Fedder (Biologie)]]
[[pl:Pióro]]
[[pt:Pena]]
[[qu:Phuru]]
[[ru:Перо]]
[[simple:Feather]]
[[sk:Perie]]
[[sl:Pero]]
[[sh:Perje]]
[[fi:Höyhen]]
[[sv:Fjäder (biologi)]]
[[ta:இறகு]]
[[tr:Tüy]]
[[uk:Пташине перо]]
[[zh:羽毛]]

Revision as of 12:07, 21 November 2009

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