Editing Hummingbird (section)

===Heat dissipation===

The high metabolic rate of hummingbirds &ndash; especially during rapid forward flight and hovering &ndash; produces increased body heat that requires specialized mechanisms of [[thermoregulation]] for heat dissipation, which becomes an even greater challenge in hot, humid climates.<ref name="powers">{{Cite journal |last1=Powers |first1=Donald R. |last2=Langland |first2=Kathleen M. |last3=Wethington |first3=Susan M. |last4=Powers |first4=Sean D. |last5=Graham |first5=Catherine H. |last6=Tobalske |first6=Bret W. |year=2017 |title=Hovering in the heat: effects of environmental temperature on heat regulation in foraging hummingbirds |journal=Royal Society Open Science |volume=4 |issue=12 |page=171056 |doi=10.1098/rsos.171056 |issn=2054-5703 |pmc=5750011 |pmid=29308244}}</ref> Hummingbirds dissipate heat partially by [[evaporation]] through exhaled air, and from body structures with thin or no feather covering, such as around the eyes, shoulders, under the wings ([[patagium|patagia]]), and feet.<ref name="evang">{{Cite journal |last1=Evangelista |first1=Dennis |last2=Fernández |first2=María José |last3=Berns |first3=Madalyn S. |last4=Hoover |first4=Aaron |last5=Dudley |first5=Robert |year=2010 |title=Hovering energetics and thermal balance in Anna's hummingbirds (''Calypte anna'') |url=https://www.researchgate.net/publication/42638033 |journal=Physiological and Biochemical Zoology |volume=83 |issue=3 |pages=406–413 |doi=10.1086/651460 |issn=1522-2152 |pmid=20350142 |s2cid=26974159}}</ref><ref name="soniak">{{Cite web |first=Matt|last=Soniak |date=2 February 2016 |title=Infrared video shows how hummingbirds shed heat through their eyes and feet |url=https://www.mentalfloss.com/article/74571/infrared-video-shows-how-hummingbirds-shed-heat-through-their-eyes-and-feet |access-date=14 January 2020 |publisher=Mental Floss}}</ref>

While hovering, hummingbirds do not benefit from the heat loss by [[convection|air convection]] during forward flight, except for air movement generated by their rapid wing-beat, possibly aiding convective heat loss from the extended feet.<ref name=powers/><ref name="udvardy">{{Cite journal |first=Miklos D.F.|last=Udvardy |date=1983 |title=The role of the feet in behavioral thermoregulation of hummingbirds |url=https://sora.unm.edu/sites/default/files/journals/condor/v085n03/p0281-p0285.pdf |journal=Condor |volume=85 |issue=3 |pages=281–285 |doi=10.2307/1367060|jstor=1367060 }}</ref> Smaller hummingbird species, such as the calliope, appear to adapt their relatively higher [[surface-to-volume ratio]] to improve convective cooling from air movement by the wings.<ref name=powers/> When air temperatures rise above {{Convert|36|C}}, thermal gradients driving heat passively by convective dissipation from around the eyes, shoulders, and feet are reduced or eliminated, requiring heat dissipation mainly by evaporation and [[exhalation]].<ref name=powers/> In cold climates, hummingbirds retract their feet into breast feathers to eliminate skin exposure and minimize heat dissipation.<ref name=udvardy/>