The chimney swift (Chaetura pelagica) is a bird belonging to the swift family Apodidae. A member of the genus Chaetura, it is closely related to both Vaux's swift and Chapman's swift; in the past, the three were sometimes considered to be conspecific. It has no subspecies. The chimney swift is a medium-sized, sooty gray bird with very long, slender wings and very short legs. Like all swifts, it is incapable of perching, and can only cling vertically to surfaces.
The chimney swift feeds primarily on flying insects, but also on airborne spiders. It generally mates for life. It builds a bracket nest of twigs and saliva stuck to a vertical surface, which is almost always a human-built structure, typically a chimney. The female lays eggs. The altricial young hatch after and fledge a month later. The average chimney swift lives .
Taxonomy and systematics
When Carl Linnaeus first described the chimney swift in 1758, he named it , believing it to be a swallow. This misconception continued well into the 1800s, with ornithologists calling it "American Swallow" (e.g. Mark Catesby) or "Chimney Swallow" (e.g. John James Audubon). In 1825, James Francis Stephens moved this and other small, short-tailed New World swifts to the genus Chaetura, where it has since remained, although some authorities in the 1800s assigned it to a variety of now obsolete genera. It has no subspecies. The chimney swift's closest relative is Vaux's swift. Scientists believe that the two species evolved from a common ancestor that was forced to North America's southeastern and southwestern corners by glacial advances. Separated for millennia by vast ice sheets, the survivors evolved into two species which are still separated by a wide gap across the continent's midsection. It is also closely related to the Chapman's swift; in the past, the three were sometimes treated as a single species.
The chimney swift's genus name, Chaetura, is a combination of two Ancient Greek words: chaite, which means "bristle" or "spine", and oura which means "tail". This is an apt description of the bird's tail, as the shafts of all ten tail feathers (rectrices) end in sharp, protruding points. The specific name pelagica is derived from the Greek word pelagikos, which means "of the sea". This is thought to be a reference to its nomadic lifestyle rather than to any reference to the sea, a theory strengthened by the later assignment of the specific name pelasgia (after the nomadic Pelasgi tribe of ancient Greece) to the same species by other ornithologists. Its common name refers to its preferred nesting site and its speedy flight.
Description
This is a medium-sized swift, measuring from in length, with a wingspan of and a weight ranging from . The sexes are identical in plumage, though males average slightly heavier than females. The adult's plumage is a dark sooty olive above and grayish brown below, with a slightly paler rump and uppertail covert feathers, and a significantly paler throat. Its upperparts are the most uniformly colored of all the Chaetura swifts, showing little contrast between back and rump. Its beak is black, as are its feet and legs. Its iris is dark brown. Juvenal plumage (that held by juvenile birds) is very similar to that of adults, but with whitish tips to the outer webs of the secondaries and tertials.
The chimney swift's wings are slender, curved and long, extending as much as beyond the bird's tail when folded. Its wingtips are pointed, which helps to decrease air turbulence (and therefore drag) during flight. Its humerus (the bone in the inner part of the wing) is quite short, while the bones farther out (more distally) along the wing are elongated, a combination which allows the bird to flap very quickly. 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. 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.
The legs of the chimney swift, like those of all swifts, are very short. Its feet are small but strong, with very short toes that are tipped with sharp, curved claws. The toes are 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 scales; instead, they are covered with smooth skin.