Editing Bird (section)

===Flight===
{{Main|Bird flight|Flightless birds}}
[[File:Restless flycatcher04.jpg|left|alt=Black bird with white chest in flight with wings facing down and tail fanned and down pointing| thumb|[[Restless flycatcher]] in the downstroke of flapping flight]]
Most birds can [[Flying and gliding animals|fly]], which distinguishes them from almost all other vertebrate classes. Flight is the primary means of locomotion for most bird species and is used for searching for food and for escaping from predators. Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb ([[Bird wing|wing]]) that serves as an [[airfoil|aerofoil]].<ref name="Gill"/>

Wing shape and size generally determine a bird's flight style and performance; many birds combine powered, flapping flight with less energy-intensive soaring flight. About 60 extant bird species are [[Flightless bird|flightless]], as were many extinct birds.<ref>{{Cite book|last=Roots |first=Clive |year=2006 |title=Flightless Birds |location=Westport |publisher=Greenwood Press |isbn=978-0-313-33545-7}}</ref> Flightlessness often arises in birds on isolated islands, most likely due to limited resources and the absence of [[mammal]]ian land predators.<ref>{{Cite journal|last=McNab |first=Brian K. |date=October 1994 |title=Energy Conservation and the Evolution of Flightlessness in Birds |journal=The American Naturalist |volume=144 |issue=4 |pages=628–642 |doi=10.1086/285697 |jstor=2462941 |bibcode=1994ANat..144..628M }}</ref> Flightlessness is almost exclusively correlated with [[Island gigantism|gigantism]] due to an island's inherent condition of isolation.<ref>{{cite book |doi=10.1016/B978-0-323-99931-1.00012-X |chapter=Dwarfing and gigantism in Quaternary vertebrates |title=Encyclopedia of Quaternary Science |date=2025 |last1=Palombo |first1=Maria Rita |last2=Moncunill-Solé |first2=Blanca |pages=584–608 |isbn=978-0-443-29997-1 }}</ref><ref>{{cite book |doi=10.1016/B978-012226865-6/00517-1 |chapter=Oceanic Islands: Models of Diversity |title=Encyclopedia of Biodiversity |date=2007 |last1=Gillespie |first1=Rosemary G. |pages=1–13 |isbn=978-0-12-226865-6 }}</ref> Although flightless, penguins use similar musculature and movements to "fly" through the water, as do some flight-capable birds such as [[auk]]s, [[shearwater]]s and [[dipper]]s.<ref>{{cite journal |last1=Kovacs |first1=Christopher E. |last2=Meyers |first2=Ron A. |title=Anatomy and histochemistry of flight muscles in a wing-propelled diving bird, the Atlantic Puffin, ''Fratercula arctica'' |journal=Journal of Morphology |date=May 2000 |volume=244 |issue=2 |pages=109–125 |doi=10.1002/(SICI)1097-4687(200005)244:2<109::AID-JMOR2>3.0.CO;2-0 |pmid=10761049 }}</ref>
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