Editing Feather (section)

==Structures and characteristics==
[[File:Feather_zipping_microstructure.svg|thumb|left|Feather microstructure showing interlocking barbules]]
[[File:pigeon_down_SEM.tif|thumb|Anterior region of a contour feather from a [[rock dove]], visualized using [[scanning electron microscopy]]. Interlocking barbules are clearly seen in the middle image.]]
Feathers are among the most complex [[Integumentary system|integumentary]] [[appendages]] found in [[Vertebrata|vertebrates]] and are formed in tiny follicles in the [[Epidermis (zoology)|epidermis]], or outer skin layer, that produce [[keratin]] [[protein]]s. The [[β-keratin]]s in feathers, [[beak]]s and [[claw]]s – and the claws, [[scale (zoology)|scales]] and [[Exoskeleton|shells]] 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-keratin]]s of mammalian [[hair]], [[horn (anatomy)|horns]] and [[hooves]].<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|first1= R. |last1= Schor |first2= S. |last2= Krimm |doi=10.1016/S0006-3495(61)86904-X |pmid=19431311 |pmc=1366335 |bibcode=1961BpJ.....1..489S}}</ref><ref>{{Cite journal|title=The Structure of Feather Rachis Keratin| first1= Linus |last1= Pauling |first2= Robert B. |last2= 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| bibcode = 1951PNAS...37..256P | doi-access= free }}</ref> The exact [[signal]]s 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|last1=Hornik| first1= C.|last2= Krishan|first2=K.|last3= Yusuf|first3=F.|last4= Scaal| first4= M.|last5= Brand-Saberi| first5= 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|doi-access= free}}</ref>

===Classification===
{{See also|Pennaceous feather|Down feather}}
[[File:Grand Cormoran (Phalacrocorax carbo), Parc de Woluwé, Bruxelles (50915141282).jpg|left|thumb|Filoplumes can be important in nuptial display; in the [[great cormorant]] they are white, and produced on the head and upper neck at the start of the breeding season, and shed soon after nesting.]]
[[File:Parrot-feather.jpg|thumb|Feather structure of a [[blue-and-yellow macaw]]]]
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 entire body. A third rarer type of feather, the '''filoplume''', is hairlike and are closely associated with pennaceous feathers and are often entirely hidden by them, with one or two filoplumes attached and sprouting from near the same point of the skin as each pennaceous feather, at least on a bird's head, neck and trunk.<ref name="Nitzsch1867">{{cite book |last=Nitzsch |first=Christian Ludwig |title=Nitzsch's Pterylography |url=https://archive.org/details/nitzschspterylog00nitzrich |year=1867 |publisher=Ray Society |page=[https://archive.org/details/nitzschspterylog00nitzrich/page/14 14] }}</ref><ref name="Chandler261">{{Harvnb|Chandler|1916|p=261}}</ref> Filoplumes are entirely absent in [[ratite]]s.<ref>{{cite journal | last=Chandler | first=Asa C. | year=1916 | title=A study of the structure of feathers, with reference to their taxonomic significance | journal=University of California Publications in Zoology| volume=13| issue=11| pages=243–446 [284] |url=https://www.biodiversitylibrary.org/page/34806138 }}</ref> In some passerines, filoplumes arise exposed beyond the pennaceous feathers on the neck.<ref name=Prum2002/> The remiges, or [[flight feather]]s of the wing, and rectrices, or 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 '''barbs'''; the barbs themselves are also branched and form the '''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 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|last= McLelland| first=J.|publisher=W.B. Saunders Co.|year=1991|isbn=0-7216-3536-9}}</ref>

Hatchling birds of some species have a special kind of natal down feathers (neossoptiles) which 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 has been observed that the orientation pattern of β-keratin fibers in the feathers of flying birds differs from that in flightless birds: the fibers are better aligned along the shaft axis direction towards the tip,<ref>{{Cite journal|last1= Cameron| first1= G.|last2=Wess|first2= T. |last3= Bonser |first3=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=118–23|doi=10.1016/S1047-8477(03)00142-4|pmid=12972348}}</ref><ref>{{Cite journal| last1= Bonser| first1= R.| last2= Saker|first2= L.| last3= Jeronimidis |first3= 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| bibcode = 2004JMatS..39.2895B | s2cid= 135873731}}</ref> and the lateral walls of rachis region show structure of crossed fibers.<ref name="Wang 2016 1600360">{{Cite journal |last=Wang |first=Bin |title=Light like a feather: A fibrous natural composite with a shape changing from round to square |journal=Advanced Science |volume=4 |issue=3 |year=2016 |doi=10.1002/advs.201600360 |pmid=28331789 |page=1600360|pmc=5357985 }}</ref><ref>{{Cite journal |last=Lingham-Soliar |first=Theagarten |title=A new helical crossed-fibre structure of b-keratin in flight feathers and its biomechanical implications |journal=PLOS ONE|year=2013 |doi=10.1371/journal.pone.0065849 |pmid=23762440 |volume=8 |issue=6 |page=e65849|bibcode=2013PLoSO...865849L |pmc=3677936 |doi-access=free }}</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.<ref name="Wang 2016 1600360"/> Some species have a [[Crest (feathers)|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 serve as camouflage for predators looking for a meal. As with fish, the top and bottom colors may be different, in order 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 the 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|first1= Muir D. |last1= Eaton |first2= Scott M. |last2= 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| last1= Bostwick| first1= Kimberly S.| last2= Richard O.| first2= Prum| year= 2005| journal= Science| volume= 309| issue= 5735| page= 736| doi= 10.1126/science.1111701| pmid= 16051789| s2cid= 22278735| url= http://cumv.bio.cornell.edu/pdf/Bostwick_Prum_2005_manuscript.pdf| access-date= 19 July 2010| url-status= live| archive-url= https://web.archive.org/web/20100707152805/http://cumv.bio.cornell.edu/pdf/Bostwick_Prum_2005_manuscript.pdf| archive-date= 7 July 2010}}</ref>
[[File:GuineaFeather.jpg|thumb|left|A contour feather from a [[Guinea fowl]]]]
Some birds have a supply of [[powder down]] feathers that 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 in pennaceous feathers. They may be scattered in plumage as 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 powder down 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 then become waterlogged, causing the bird to 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 to reduce buoyancy, thereby allowing the birds to swim submerged.<ref>{{Cite journal| last1= Ribak| first1= G.| last2= Weihs| first2= D. | last3= Arad| first3= 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|issue=2}}</ref>
[[File: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 found around the eyes and bill. They may serve a similar purpose to [[eyelash]]es and [[vibrissae]] in [[mammal]]s. Although there is as yet no clear evidence, it has been suggested that rictal bristles have sensory functions and may help insectivorous birds to capture prey.<ref>{{Cite journal |url=http://sora.unm.edu/sites/default/files/journals/wilson/v084n02/p0193-p0197.pdf |title=The role of avian rictal bristles |last=Lederer |first=Roger J. |year=1972 |journal=[[The Wilson Bulletin]] |volume=84 |pages=193–97 |url-status=live |archive-url=https://web.archive.org/web/20140204025111/http://sora.unm.edu/sites/default/files/journals/wilson/v084n02/p0193-p0197.pdf |archive-date=4 February 2014 }}</ref> In one study, willow flycatchers (''[[Empidonax traillii]]'') were found to catch insects equally well before and after removal of the rictal bristles.<ref>{{Cite journal|url=http://sora.unm.edu/node/103116|last1=Conover|first1=M. R.|last2=Miller|first2=D. E.|year=1980|title=Rictal bristle function in willow flycatcher|journal=Condor|volume=82|pages=469–471|issue=4|doi=10.2307/1367580|url-status=live|archive-url=https://web.archive.org/web/20140222004514/https://sora.unm.edu/node/103116|archive-date=22 February 2014|jstor=1367580|url-access=subscription}}</ref>

[[Grebe]]s are peculiar in their habit of ingesting their own feathers and feeding them to their young. Observations on their diet of fish and the frequency of feather eating suggest that ingesting feathers, particularly down from their flanks, aids in forming easily ejectable pellets.<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|last1= Piersma| first1= T |first2= M. R. |last2=van Eerden|journal=Ibis|volume=131|issue=4|pages=477–486| year= 1989| doi=10.1111/j.1474-919X.1989.tb04784.x|url= https://pure.rug.nl/ws/files/979340584/Ibis_-_October_1989_-_PIERSMA_-_Feather_eating_in_Great_Crested_Grebes_Podiceps_cristatus_a_unique_solution_to_the.pdf}}</ref>

===Distribution===
[[File: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|jstor=1364475|last=Demay|first=Ida S.|journal=The Condor|url=http://sora.unm.edu/node/99003|volume=42|issue=2|year=1940|pages=112–118|doi=10.2307/1364475|url-status=live|archive-url=https://web.archive.org/web/20140221153848/https://sora.unm.edu/node/99003|archive-date=21 February 2014|url-access=subscription}}</ref> In most birds the feathers grow from specific tracts of skin called ''pterylae''; between the pterylae there are regions which are free of feathers called ''apterylae'' (or ''apteria''). Filoplumes and down may arise from the apterylae. 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=Hall, K. |author2= Susanna S. |doi=10.1007/s10336-004-0070-5| bibcode= 2005JOrni.146..121H| s2cid= 36055848}}</ref><ref>{{Cite journal|last= Pycraft| first=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|issue=3| url=https://www.biodiversitylibrary.org/part/382407}}</ref> Species that incubate their own eggs often lose their feathers on a region of their belly, forming a [[brooding patch]].<ref>{{Cite journal|last=Turner|first=J. Scott|year=1997|title=On the Thermal Capacity of a Bird's Egg Warmed by a Brood Patch|url=https://www.esf.edu/efb/turner/publication%20pdfs/thermal%20capacity%20of%20eggs.pdf|journal=Physiological Zoology|volume=70|issue=4|pages=470–80|doi=10.1086/515854|pmid=9237308|s2cid=26584982|via=EBSCO|access-date=29 July 2020|archive-date=20 October 2022|archive-url=https://web.archive.org/web/20221020202108/https://www.esf.edu/efb/turner/publication%20pdfs/thermal%20capacity%20of%20eggs.pdf|url-status=dead}}</ref>

===Coloration===
[[File:Red feather pigments.jpg|thumb|left|Colors resulting from different feather pigments<br />'''Left:''' [[turacin]] (red) and [[turacoverdin]] (green, with some structural blue [[iridescence]] at lower end) on the wing of ''[[Tauraco bannermani]]''<br />'''Right:''' [[carotenoid]]s (red) and [[melanin]]s (dark) on belly/wings of ''[[Ramphocelus bresilius]]'']]
The colors of feathers are produced by pigments, by microscopic structures that can [[refraction|refract]], reflect, or scatter selected wavelengths of light, or by a combination of both.

Most feather pigments are [[melanin]]s (brown and beige [[pheomelanin]]s, black and grey [[eumelanin]]s) and [[carotenoid]]s (red, yellow, orange); other pigments occur only in certain [[taxa]] – the yellow to red [[psittacofulvin]]s<ref>{{Cite journal|journal=Biology Letters|title=Distribution of unique red feather pigments in parrots|volume=1|issue=1|pages=38–43|year=2005|last1= McGraw |first1=KH |first2= MC |last2= Nogare| doi=10.1098/rsbl.2004.0269| pmid= 17148123|pmc=1629064}}</ref> (found in some [[parrot]]s) and the red [[turacin]] and green [[turacoverdin]] ([[porphyrin]] pigments found only in [[turaco]]s).

[[Structural coloration]]<ref name=pettingill/><ref>{{Cite journal| last1= Hausmann| first1= F.| last2= Arnold| first2=K.E.| last3= Marshall| first3= N.J. | last4= Owens| first4= I.P.F.|year=2003|title=Ultraviolet signals in birds are special|journal=Proceedings of the Royal Society 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|first1= Matthew D|last1= Shawkey|first2= Geoffrey E|last2= 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|pmid= 17148144|pmc= 1626226|archive-url= https://web.archive.org/web/20090326144121/http://nature.berkeley.edu/%7Emshawkey/9.pdf|archive-date= 26 March 2009}}</ref> is involved in the production of blue colors, [[iridescence]], most [[ultraviolet]] reflectance and in the enhancement of pigmentary colors. Structural iridescence has been reported<ref>{{Cite journal |last1= Vinther |first1= Jakob |first2= Derek E. G. |last2= Briggs |first3= Julia |last3= Clarke |first4= Gerald |last4= Mayr |first5= Richard O. |last5= Prum |year= 2009 |pages= 128–31 |issue= 1 |volume= 6 |title= Structural coloration in a fossil feather |journal= [[Biology Letters]] |doi= 10.1098/rsbl.2009.0524 |pmc= 2817243 |pmid= 19710052 |url= http://www.eeb.yale.edu/prum/pdf/Vinther%20et%20al%202010.pdf |access-date= 19 July 2010 |archive-url= https://web.archive.org/web/20100621083621/http://www.eeb.yale.edu/prum/pdf/Vinther%20et%20al%202010.pdf |archive-date= 21 June 2010 }}</ref> in fossil feathers dating back 40 million years. White feathers lack pigment and scatter light diffusely; [[albinism in birds]] is caused by defective pigment production, though structural coloration will not be affected (as can be seen, for example, in blue-and-white [[budgerigar]]s).

[[File:BWfeather.jpg|thumb|upright|A feather with no pigment]]
The blues and bright greens of many [[parrot]]s are produced by constructive interference of light reflecting from different layers of structures in feathers. In the case of green plumage, in addition to yellow,<!-- was: carotinoid, but according to the psittacofulvin source Psittaciformes this might not be correct --> the specific feather structure involved is called by some the Dyck texture.<ref>{{Cite journal|last= Dyck |first=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|last1=Shawkey|first1=M. D.|first2=G. E.|last2=Hill|doi=10.1642/0004-8038(2004)121[0652:FAAFS]2.0.CO;2|doi-access=free}}</ref> Melanin is often involved in the absorption of light; in combination with a yellow pigment, it produces a dull olive-green.

[[File:Pedro Américo - D. Pedro II na abertura da Assembléia Geral (cropped).jpg|thumb|Emperor [[Pedro II of Brazil]] wearing a wide collar of orange toucan feathers around his shoulders and elements of the [[Imperial Regalia of Brazil|Imperial Regalia]]. Detail from a painting by [[Pedro Américo]]]]
In some birds, feather colors may be created, or altered, by secretions from the [[uropygial gland]], also called the preen gland. The yellow bill colors of many hornbills are produced by such secretions. It has been suggested that there are other color differences that may be visible only in the ultraviolet region,<ref name=delhey>{{Cite journal|last1=Delhey|first1=K|first2=A.|last2=Peters|first3=B.|last3=Kempenaers|year=2007|title=Cosmetic coloration in birds: occurrence, function and evolution|journal=Am. Nat.|volume=169|issue=S1|pages=S145–158|url=http://www.orn.mpg.de/documents/peters/Delhey_AmNat2007_copy.pdf|doi=10.1086/510095|pmid=19426089|bibcode=2007ANat..169S.145D|s2cid=29592388|archive-url=https://web.archive.org/web/20071203190459/http://www.orn.mpg.de/documents/peters/Delhey_AmNat2007_copy.pdf|archive-date=3 December 2007}}</ref> but studies have failed to find evidence.<ref>{{Cite journal|last1= Delhey| first1= K.| first2= A. |last2= Peters| first3= P. H. W.| last3= Biedermann |first4= B. |last4= 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=939–46| pmid= 18560743| issue= 10| bibcode = 2008NW.....95..939D |doi-access= free|hdl= 11858/00-001M-0000-0010-509C-A|hdl-access= free}}</ref> The oil secretion from the uropygial gland may also have an inhibitory effect on feather bacteria.<ref>{{Cite journal|last1=Shawkey|first1=M. D.|first2=S. R.|last2=Pillai|first3=G. E.|last3=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|doi=10.1111/j.0908-8857.2003.03193.x|issue=4|archive-url=https://web.archive.org/web/20080910205855/http://nature.berkeley.edu/~mshawkey/2.pdf|archive-date=10 September 2008}}</ref>

The reds, orange and yellow colors of many feathers are caused by various carotenoids. Carotenoid-based pigments might be honest signals of fitness because they are derived from special diets and hence might be difficult to obtain,<ref>{{cite journal | doi = 10.2307/2408316 | pmid = 28563214 | last1 = Endler | first1 = J. A. | year = 1980 | title = Natural selection on color patterns in Poeci-lia reticulata | jstor = 2408316| journal = Evolution | volume = 34 | issue = 1| pages = 76–91 }}</ref><ref>{{Cite journal|last1= Badyaev |first1=A. V. |last2= Hill |first2= G. E.| 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|issue=2|s2cid=201965078 |doi-access=free}}</ref> and/or because carotenoids are required for immune function and hence sexual displays come at the expense of health.<ref>{{cite journal | last= Lozano |first= G. A. |s2cid= 86971117 | year = 1994 | title = Carotenoids, parasites, and sexual selection |journal = Oikos | volume = 70 |issue= 2 | pages = 309–311 | doi=10.2307/3545643|jstor= 3545643 |bibcode= 1994Oikos..70..309L }}</ref>

A bird's feathers undergo wear and tear and are replaced periodically during the bird's life through [[molt]]ing. New feathers, known when developing as [[pin feather|blood, or pin feathers]], depending on the stage of growth, are formed through the same follicles from which the old ones were fledged. The presence of melanin in feathers increases their resistance to abrasion.<ref>{{Cite journal|last=Bonser|first=R. H. C.|year=1995|title=Melanin and the abrasion resistance of feathers|jstor=1369048|journal=Condor|url=http://sora.unm.edu/node/105022|volume=97|pages=590–591|doi=10.2307/1369048|issue=2|url-status=live|archive-url=https://web.archive.org/web/20140223002132/https://sora.unm.edu/node/105022|archive-date=23 February 2014|url-access=subscription}}</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?|last1=Grande|first1=J. M.|last2=Negro|first2=J. J.|first3=M. J.|last3=Torres|url=http://www.ardeola.org/files/Ardeola_51(2)_375-383.pdf|url-status=live|archive-url=https://web.archive.org/web/20080910205855/http://www.ardeola.org/files/Ardeola_51(2)_375-383.pdf|archive-date=10 September 2008}}</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; the authors cited other research also published in 2004 that stated increased melanin provided greater resistance. They observed that the greater resistance of the darker birds confirmed [[Gloger's rule]].<ref>{{Cite journal|last1=Burtt|first1=Edward H. Jr.|last2=Ichida|first2=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|s2cid=5857742|url=http://www.public.asu.edu/~kjmcgraw/pubs/Condor04b.pdf|url-status=live|archive-url=https://web.archive.org/web/20121120194024/http://www.public.asu.edu/~kjmcgraw/pubs/Condor04b.pdf|archive-date=20 November 2012}}</ref>

Although sexual selection plays a major role in the development of feathers, in particular, the color of the feathers it is not the only conclusion available. New studies are suggesting that the unique feathers of birds are also a large influence on many important aspects of avian behavior, such as the height at which different species build their nests. Since females are the prime caregivers, evolution has helped select females to display duller colors down so that they may blend into the nesting environment. The position of the nest and whether it has a greater chance of being under predation has exerted constraints on female birds' plumage.<ref name="ReferenceA">{{cite journal | last1 = Martin | first1 = T. E. | last2 = Badyaev | first2 = A. V. | year = 1996 | title = Sexual dichromatic in birds; importance of nest predation and nest location for females versus males | journal = Evolution | volume = 50 | issue = 6| pages = 2454–2460 | doi=10.2307/2410712| jstor = 2410712 | pmid = 28565684 }}</ref> A species of bird that nests on the ground, rather than the canopy of the trees, will need to have much duller colors in order not to attract attention to the nest. The height study found that birds that nest in the canopies of trees often have many more predator attacks due to the brighter color of feathers that the female displays.<ref name="ReferenceA"/> Another influence of evolution that could play a part in why feathers of birds are so colorful and display so many patterns could be due to that birds developed their bright colors from the vegetation and flowers that thrive around them. Birds develop their bright colors from living around certain colors. Most bird species often blend into their environment, due to some degree of camouflage, so if the species habitat is full of colors and patterns, the species would eventually evolve to blend in to avoid being eaten. Birds' feathers show a large range of colors, even exceeding the variety of many plants, leaf, and flower colors.<ref>{{cite journal |last1= Caswell Stoddard| first1= Mary | last2= Prum| first2= Richard O. |year=2011 |title=How colorful are birds? Evolution of the avian plumage color gamut |journal=Behavioral Ecology |volume=22 |issue=5 |pages=1042–1052 |doi=10.1093/beheco/arr088 |doi-access=free |hdl=10.1093/beheco/arr088 |hdl-access=free }}</ref>

=== Feathers used in mating displays ===
In sexually dimorphic birds, males often develop distinct coloration or specialized ornamental feathers used in mating displays to attract mates. There are several proposed theories for the origin of ornamental feathers, with the first observed instances being observed in multiple early [[Theropoda|theropods]]<ref name=":1">{{Cite journal |last1=Xu |first1=Xing |last2=Barrett |first2=Paul M. |date=2025-02-19 |title=The origin and early evolution of feathers: implications, uncertainties and future prospects |journal=Biology Letters |volume=21 |issue=2 |pages=20240517 |doi=10.1098/rsbl.2024.0517 |pmc=11837858 |pmid=39969251}}</ref><ref>{{Cite journal |last1=Campione |first1=Nicolás E. |last2=Barrett |first2=Paul M. |last3=Evans |first3=David C. |date=12 March 2020 |title=On the Ancestry of Feathers in Mesozoic Dinosaurs |url=https://link.springer.com/chapter/10.1007/978-3-030-27223-4_12 |journal=The Evolution of Feathers from Their Origin to the Present |series=Fascinating Life Sciences |pages=213–243 |doi=10.1007/978-3-030-27223-4_12 |isbn=978-3-030-27222-7 |via=Springer|url-access=subscription }}</ref> (see subsection on Origins below). 

The most well-known example of ornamental feathers used in mating is male [[Peafowl|peacocks]] (''Pavo cristatus)''. Males sport a long train of covert feathers with distinct eyespot patterns, which are coupled with a vigorous display in the courtship process. When performing these displays, males flash their train in a fanning motion, showing their plumage off to females. 

The evolutionary origin of the peacock’s ornamental feathers and display remains unclear, with multiple theories proposing a combination of factors. In a study observing peacock display behavior, captive male peacocks had the length of their trains, the length of their torsi, and the density of the eyespots measured. They were then released into enclosures with female peacocks, with their mating success measured in successful copulations. The results showed that [[female choice]] was not influenced by train size, but by eyespot density. This suggests that male peacocks’ elaborate feathers and displays evolved as a result of female choice, particularly favoring males with more eyespot patterns<ref>{{Cite journal |last1=Loyau |first1=Adeline |last2=Jalme |first2=Michel Saint |last3=Sorci |first3=Gabriele |date=2005 |title=Intra- and Intersexual Selection for Multiple Traits in the Peacock (Pavo cristatus) |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.2005.01091.x |journal=Ethology |language=en |volume=111 |issue=9 |pages=810–820 |doi=10.1111/j.1439-0310.2005.01091.x |bibcode=2005Ethol.111..810L |issn=1439-0310|url-access=subscription }}</ref>. 

==== Structure and use ====
The bone morphology of the radius, ulna, and humerus which support ornamental feathers can also affect female choice<ref name=":2">{{Cite journal |last1=Friscia |first1=Anthony |last2=Sanin |first2=Gloria D. |last3=Lindsay |first3=Willow R. |last4=Day |first4=Lainy B. |last5=Schlinger |first5=Barney A. |last6=Tan |first6=Josh |last7=Fuxjager |first7=Matthew J. |date=2016 |title=Adaptive evolution of a derived radius morphology in manakins (Aves, Pipridae) to support acrobatic display behavior |url=https://onlinelibrary.wiley.com/doi/10.1002/jmor.20534 |journal=Journal of Morphology |language=en |volume=277 |issue=6 |pages=766–775 |doi=10.1002/jmor.20534 |pmid=27027525 |issn=1097-4687|url-access=subscription }}</ref>. For example, the bone morphology of male [[Club-winged manakin|club-winged manakins]] (''Machaeropterus deliciosus'') is highly specialized, with larger and denser ulnas that are bigger in volume and have higher mineral density compared to others in the manakin family<ref name=":2" /><ref>{{Cite journal |last1=Bostwick |first1=Kimberly S. |last2=Riccio |first2=Mark L. |last3=Humphries |first3=Julian M. |date=2012-06-13 |title=Massive, solidified bone in the wing of a volant courting bird |journal=Biology Letters |volume=8 |issue=5 |pages=760–763 |doi=10.1098/rsbl.2012.0382 |pmc=3440988 |pmid=22696286}}</ref>. The secondary feathers are enlarged and are used in mating displays; males knock the tips of the enlarged feathers together repeatedly in a “jump and snap” motion, producing a distinctive sound. The display ends with a “beard up” motion, in which the male shows off their long yellow throat feathers rapidly while performing jumps.

==== Tail Length ====
Tail length is another example of feathers playing a role in mate choice, as seen in the [[long-tailed widowbird]] (''Euplectes progne''). The males of this species have extremely long tail feathers during the mating season, which correlates with higher success in attracting mates<ref name=":3">{{Cite journal |last=Andersson |first=Malte |date=October 1982 |title=Female choice selects for extreme tail length in a widowbird |url=https://www.nature.com/articles/299818a0 |journal=Nature |language=en |volume=299 |issue=5886 |pages=818–820 |doi=10.1038/299818a0 |bibcode=1982Natur.299..818A |issn=1476-4687|url-access=subscription }}</ref>. In a famous study testing the correlation between tail length and [[Fitness (biology)|fitness]], male widowbirds had their tail lengths artificially shortened or elongated and those with elongated tails had higher mating success. It was alternatively proposed that longer ornamental feathers played a role in territory defense and intrasexual competition, as a way of displaying dominance, but there was  no substantial evidence supporting this theory<ref name=":3" />.

==== Origin of ornamental feathers ====
One possible origin of ornamental feathers is in the megalosauroid ''[[Sciurumimus]]'', which have a simple, monofilamentous morphology. Monofilamentous feathers have a single, thread-like structure, as opposed to branches or barbs, and are considered to be the earliest form of feather<ref name=":1" />. Monofilamentous feathers have also been found in a wide range of taxa, though ''Sciurumimus'' was the earliest. Monofilamentous feathers have also been found in the tyrannosauroid ''[[Yutyrannus]]'' and the therizinosauroid ''[[Beipiaosaurus]]'', with proportionally broader monofilaments that were likely a form of early specialized ornamental feathers<ref name=":1" />. 

An analysis of feathers discovered in Burmese [[amber]] revealed unusual coloration along the [[rachis]], suggesting they bore striking color patterns. Early ornamental feathers in the genus ''[[Schizooura]]'' suggest an aerodynamic use as well as an ornamental one, with the pin-tailed shape being too narrow to impact aerodynamics<ref name=":1" />.