Editing Feather (section)

===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}}</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>