Editing Hummingbird (section)

=== Perception of sweet nectar ===

Perception of sweetness in nectar evolved in hummingbirds during their [[genetic divergence]] from insectivorous swifts, their closest bird relatives.<ref name="baldwin">{{Cite journal |last1=Baldwin |first1=Maude W. |last2=Toda |first2=Yasuka |last3=Nakagita |first3=Tomoya |last4=O'Connell |first4=Mary J. |last5=Klasing |first5=Kirk C. |last6=Misaka |first6=Takumi |last7=Edwards |first7=Scott V. |last8=Liberles |first8=Stephen D. |year=2014 |title=Sensory biology. Evolution of sweet taste perception in hummingbirds by transformation of the ancestral umami receptor |journal=Science |volume=345 |issue=6199 |pages=929–933 |bibcode=2014Sci...345..929B |doi=10.1126/science.1255097 |pmc=4302410 |pmid=25146290}}</ref> Although the only known sweet sensory receptor, called [[TAS1R2|T1R2]],<ref>{{Cite journal |last=Li|first=X. |year=2009 |title=T1R receptors mediate mammalian sweet and umami taste |journal=American Journal of Clinical Nutrition |volume=90 |issue=3 |pages=733S–37S |doi=10.3945/ajcn.2009.27462G |pmid=19656838 |doi-access=free}}</ref> is absent in birds, receptor expression studies showed that hummingbirds adapted a carbohydrate receptor from the [[TAS1R1|T1R1]]-[[TAS1R3|T1R3]] receptor, identical to the one perceived as [[umami]] in humans, essentially repurposing it to function as a nectar sweetness receptor.<ref name="baldwin"/> This adaptation for taste enabled hummingbirds to detect and exploit sweet nectar as an energy source, facilitating their distribution across geographical regions where nectar-bearing flowers are available.<ref name="baldwin"/>