Editing Feather (section)

===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>