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. Many fly around all day and only come down at night when roosting.
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 .
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 (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 Pelasgians of ancient Greece) to the same species by other ornithologists. Its common name refers to its preferred nesting site and its speedy flight.
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.
Its tail is short and square, measuring only in length. All ten of its tail feathers have shafts which extend as much as beyond the vanes, ending in sharp, stiff points. These help the bird to prop itself against vertical surfaces.
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. It is far-sighted and, like some birds of prey, this swift is bifoveal: each eye having both a temporal and a Fovea centralis. These are small depressions in the retina where visual acuity is highest, and help to make its vision especially . Like most , it is able to focus both eyes at once; however, it is also able to focus a single eye independently.
Its beak is very small, with a culmen that measures a mere in length. However, its gape is huge, extending back below its eyes, and allowing the bird to open its mouth very widely. Unlike many insectivorous birds, it lacks rictal bristles at the base of the beak.
The chimney swift's wintering grounds were only discovered in 1944, when bands from birds ringed (ringed) in North America were recovered in Peru. An indigenous Peruvian had been wearing the bands as a necklace.
During the breeding season, at least half of the chimney swift's forays occur within of its nest; however, it ranges up to away. While most of its food is seized following aerial pursuit, some is gleaned from the foliage of trees; the bird hovers near the ends of branches or drops through upper canopy levels. The chimney swift generally flies quite high, though it descends during cold or rainy weather. When feeding, it regularly occurs in small groups, and sometimes hunts with , particularly and ; in mixed-species flocks, it is typically among the lower fliers. There is at least one record of a chimney swift attempting to kleptoparasitism a dragonfly from a purple martin, and it has been observed chasing other purple martins. In general, it is a diurnality feeder which remains active into early evening. However, there are records, particularly during migration periods, of chimney swifts feeding well after dark over brightly lit buildings.
The species shows two-weight peaks each year: one at the start of the breeding season, and a higher one shortly before it begins its migration south in the autumn. Its lowest weights are typically recorded during the breeding season, when it also begins a complete molt of its plumage. The chimney swift's weight gain before bird migration is smaller than that of some passerines, suggesting that it must refuel en route at various stopover points.
Before the arrival of European colonists into North America, the chimney swift nested in hollow trees; now, it uses human-built structures almost exclusively. While the occasional nest is still built in a hollow tree (or, exceptionally, in an abandoned woodpecker nest), most are now found inside , with smaller numbers in airshafts, the dark corners of lightly used buildings, , or water well. The bird nest is a shallow bracket made of sticks, which the birds gather in flight, breaking them off trees. The sticks are glued together (and the nest to a vertical surface) with copious amounts of the bird's saliva. During the breeding season, each adult's more than double in size, from in the non-breeding season to during the breeding season.
Unlike some swift species, which mating in flight, chimney swifts mate while clinging to a vertical surface near their nest. They daily, until the clutch is complete. The female typically lays , though clutch sizes range from . The eggs, which are long and elliptical in shape, are moderately glossy, smooth and white, and measure . Each weighs nearly of the female's body weight. avian incubation by both parents, the eggs hatch after . Baby chimney swifts are altricial—naked, blind and helpless when they hatch. Fledglings leave the nest after a month.
The average chimney swift's life span is , but one is known to have lived more than . It was originally banded as an adult, and was recaptured in another banding operation some later.
The chimney swift carries a number of internal and external parasites. It is the type host for the nematode species Aproctella nuda, the feather mite species Euchineustathia tricapitosetosa, and the bird louse species Dennyus dubius, and is also known to carry the tapeworm species Pseudochoanotaenia collocaliae. Its nest is known to host the Hemiptera species Cimexopsis nyctali, which is similar to the bed bug and can (on rare occasions) become a pest species in houses.
After sudden temperature drops, the chimney swift sometimes hunts low over concrete roads (presumably following insect prey drawn to the warmer road), where collisions with vehicles become more likely. Severe storms, such as , encountered during migration can seriously impact the chimney's swift's survival rates. Swifts caught up in 2005's Hurricane Wilma were swept as far north as Atlantic Canada and Western Europe. More than 700 were found dead. The following year, roost counts in the province of Quebec, Canada showed a decrease of 62 percent, and the overall population in the province was halved.
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