Editing Chimney swift (section)

==Description==

This is a medium-sized swift, measuring from {{convert|12|to|15|cm|in|abbr=on}} in length,{{#tag:ref|By convention, length is measured from the tip of the bill to the tip of the tail on a dead bird (or skin) laid on its back.<ref name = "HBW"/>|group="nb"}} with a wingspan of {{convert|27|to|30|cm|in|abbr=on}} and a weight ranging from {{convert|17|to|30|g|oz|abbr=on}}.<ref name = "Cornell"/> The sexes are identical in plumage,<ref name = "Johnston"/> though males average slightly heavier than females.<ref name = "Johnston"/> The adult's [[plumage]] is a dark sooty olive above and grayish brown below, with a slightly paler rump and uppertail [[covert feather]]s, and a significantly paler throat.<ref name = "Ridgely"/> Its upperparts are the most uniformly colored of all the ''Chaetura'' swifts, showing little contrast between back and rump.<ref name = "Chantler185"/> Its beak is black, as are its feet and legs. Its [[iris (anatomy)|iris]] is dark brown.<ref name = "Barrows"/> The [[juvenile (organism)|juvenile]] plumage (held by young birds for their first few months after fledging) is very similar to that of adults, but with whitish tips to the outer webs of the [[Flight feather#Secondaries|secondaries]] and [[Flight feather#Tertials|tertials]].<ref name = "NatWeb"/>

The chimney swift's wings are slender, curved and long,<ref name = "Dunne2"/> extending as much as {{convert|1.5|in|cm|abbr=on}} beyond the bird's tail when folded.<ref name = "Blanchan"/> Its wingtips are pointed, which helps to decrease air turbulence (and therefore [[drag (physics)|drag]]) during flight.<ref name = "Henderson"/> Its [[humerus]] (the bone in the inner part of the wing) is quite short, while the bones farther out (more [[Anatomical terms of location#Proximal and distal|distal]]ly) along the wing are elongated, a combination which allows the bird to flap very quickly.<ref name = "Sibley2"/> In flight, it holds its wings stiffly, alternating between rapid, quivering flaps and longer glides. Its flight profile is widely described as a "cigar with wings"—a description first used by [[Roger Tory Peterson]].<ref name = "Dunne2"/> Although the bird often appears to beat its wings asynchronously during flight, photographic and stroboscopic studies have shown that it beats them in unison. The illusion that it does otherwise is heightened by its very fast and highly erratic flight, with many rapid changes of direction.<ref name = "Savile"/>

The legs of the chimney swift, like those of all swifts, are very short.<ref name = "Coues"/> Its feet are small but strong, with very short toes that are tipped with sharp, curved claws.<ref name = "Sibley2"/> The toes are [[dactyly#In birds|anisodactyl]]—three forward, one back—like those of most birds, but the chimney swift can swivel its back toe (its [[hallux]]) forward to help it get a better grip. Unlike the legs and feet of most birds, those of the chimney swift have no [[scale (anatomy)|scales]]; instead, they are covered with smooth skin.<ref name = "Kyle15"/>

Its tail is short and square,<ref name = "NatGeo"/> measuring only {{convert|1.90|to|2.15|in|cm|abbr=on|order=flip}} in length.<ref name = "Barrows"/> All ten of its tail feathers have shafts which extend as much as {{convert|0.5|in|cm|abbr=on|order=flip}} beyond the vanes, ending in sharp, stiff points.<ref name = "Kyle15"/> These help the bird to prop itself against vertical surfaces.<ref name = "Encyclopedia"/>

The chimney swift has large, deep set eyes. These are protected by small patches of coarse, black, bristly feathers, which are located in front of each eye. The swift can change the angle of these feathers, which may help to reduce [[glare (vision)|glare]]. It is [[far-sighted]] and, like some [[birds of prey]], this swift is bifoveal: each eye having both a temporal and a [[Fovea centralis|central fovea]].{{#tag:ref|For more information, see [[Bird vision#Anatomy of the eye|Anatomy of the eye]] section in the [[Bird vision]] article|group="nb"}} These are small depressions in the [[retina]] where [[visual acuity]] is highest,<ref name = "HBW5"/> and help to make its vision especially [[wikt:acute|acute]].<ref name = "Wood"/> Like most [[vertebrate]]s, it is able to [[accommodation (eye)|focus]] both eyes at once; however, it is also able to focus a single eye independently.<ref name = "HBW5"/>

Its [[beak|bill]] is very small, with a [[culmen (bird)|culmen]] that measures a mere {{convert|5|mm|in|abbr=on}} in length.<ref name = "Chantler187"/> However, its [[gape]] is huge, extending back below its eyes, and allowing the bird to open its mouth very widely.<ref name = "Americana"/> Unlike many insectivorous birds, it lacks [[beak#Rictal bristles|rictal bristles]] at the base of the beak.<ref name = "Surface"/>

===Similar species===
The chimney swift looks very much like the closely related Vaux's swift, but is slightly larger, with relatively longer wings and tail, slower wingbeats<ref name = "Sibley"/> and a greater tendency to soar.<ref name = "NatGeo"/> It tends to be darker on the breast and rump than the Vaux's swift, though there is some overlap in [[plumage]] coloring.<ref name = "Sibley"/> It can be as much as 30 percent heavier than Vaux's swift, and its wings, which are proportionately narrower, show a pronounced bulge in the inner secondaries.<ref name = "SibleyWeb"/> The chimney swift is smaller, paler and shorter tailed than the [[black swift]].<ref name = "Sibley"/> In [[Central America]], it is most similar to [[Chapman's swift]], but it is paler (matte olive rather than glossy black) and has a stronger contrast between its pale throat and the rest of its underparts than does its more uniformly colored relative.<ref name = "Ridgely"/>