{{short description|Area of bare skin on the underside of nesting birds}} [[File:Riparia riparia-Brutfleck.jpg|thumb|250px|alt=A bird on its back, revealing a patch of featherless skin|Brood patch of a sand martin]] A '''brood patch''', also known as an '''incubation patch''' in older literature,<ref>{{Cite journal |last=Jones |first=Richard E. |date=1971 |title=The incubation patch of birds |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1469-185X.1971.tb01048.x |journal=Biological Reviews |language=en |volume=46 |issue=3 |pages=315–339 |doi=10.1111/j.1469-185X.1971.tb01048.x |issn=1464-7931|url-access=subscription }}</ref> is an area of featherless skin on the underside of birds that exists during the nesting season. Feathers act as inherent insulators and prevent efficient incubation, to which brood patches are the solution. This patch of skin is well supplied with blood vessels at the surface, enabling heat transfer to the eggs when incubating.<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=2020-07-23|archive-date=2022-10-20|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><ref name="Ehrlich 1988">{{Cite web|last=Ehrlich|first=Paul|date=1988|title=Brood Patches|url=https://web.stanford.edu/group/stanfordbirds/text/essays/Brood_Patches.html|url-status=live|archive-url=https://web.archive.org/web/20150512043416/http://web.stanford.edu:80/group/stanfordbirds/text/essays/Brood_Patches.html |archive-date=2015-05-12 |access-date=2020-08-03|website=web.stanford.edu}}</ref>
== Location ==
The positions of brood patches can vary. Many have a single brood patch in the middle of the belly, while some shorebirds have one patch on each side of the belly. Great Auks and Razorbills develop two brood patches on the side of the body.<ref>{{cite web |last1=Birkhead |first1=Tim |author1-link=Tim Birkhead |title=The Great Auk had two brood patches |url=https://bou.org.uk/blog-birkhead-auk-brood-patches/ |website=British Ornithologists' Union |access-date=31 January 2026 |date=14 October 2021}}</ref> Gulls and Galliformes may have three brood patches.{{cn|date=February 2026}} American kestrels develop three brood patches.<ref name="Wiebe1993">{{cite journal |last1=Wiebe |first1=Karen L. |last2=Bortolotti |first2=Gary R. |author1-link=Karen L. Wiebe |title=Brood Patches of American Kestrels: An Ecological and Evolutionary Perspective |journal=Ornis Scandinavica |date=July 1993 |volume=24 |issue=3 |pages=197 |doi=10.2307/3676735 |url=https://www.jstor.org/stable/3676735 |access-date=1 February 2026|url-access=subscription }}</ref>
Pelicans, boobies, and gannets do not develop brood patches but cradle the eggs on their feet.<ref name="Ehrlich 1988" /> Brood parasitic cuckoos do not develop brood patches.<ref>Payne, R. B. 2005. ''The Cuckoos''. Oxford University Press. p. 128.</ref> In species where both parents incubate, brood patches may develop in both sexes,<ref name="Ehrlich 1988" /> though the size of the patch may vary by sex and size of the bird.<ref name="Wiebe1993" />
== Formation ==
Shortly before egg laying, hormones such as oestrogen, prolactin, and progesterone cause a bird’s belly feathers to loosen and fall out, thus forming a patch of bare skin.<ref name="RRP2025" /> In most species, the feathers in the region shed automatically, but ducks and geese may pluck and use their feathers to line the nest. Feathers regrow sooner after hatching in precocial birds than for those that have altricial young.<ref name="Ehrlich 1988" />
== Function == === Incubation === Brood patches help carry heat close to the skin surface during incubation. Additionally, birds may accumulate fat around the patch to increase its pliability.<ref name="RRP2025">{{cite web |title=What is a brood patch? |url=https://www.raptorresource.org/2025/02/03/what-is-a-brood-patch/ |website=Raptor Resource Project |access-date=31 January 2026 |date=3 February 2025}}</ref> Upon settling on a nest, birds will shift in a characteristic side to side manner to ensure full contact of the brood patch with eggs or young.<ref name="Ehrlich 1988" />
=== Clutch size === Brood patch can help regulate number of eggs produced in one cycle, or clutch size. Once eggs are laid, the touch sensors in the brood patch detect the eggs and trigger hormonal responses to limit ova production. However, if the eggs are removed or broken shortly after the eggs are laid, this hormonal regulation will not happen, and eggs can be continuously produced.<ref name="RRP2025" />
==See also== * Broodiness
==References== {{reflist}}
==External links== * [https://www.stanford.edu/group/stanfordbirds/text/essays/Brood_Patches.html Brood patches] * [https://web.archive.org/web/20070912205858/https://www.esf.edu/efb/turner/incubation%20energetics.html Incubation energetics]
Category:Bird anatomy Category:Bird breeding