The Chimney Swift (Chaetura pelagica) is a bird belonging to the swift family. It commonly nests in chimneys in eastern North America, and migrates in large flocks to northwestern South America for the winter.
Taxonomy and systematics
When he first described the Chimney Swift in 1758, Carl Linnaeus named it Hirundo pelagica, 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 the Vaux's Swift. Scientists believe that the two species evolved from a common ancestor which was forced to the continent's southeastern and southwestern corners by glacial advances. Separated for centuries 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 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.
This is a medium-sized swift, measuring from 12 to 15 cm (4.7 to 5.9 in) in length,[nb 1] with a wingspan of 27 to 30 cm (11 to 12 in) and a weight ranging from 17 to 30 g (0.60 to 1.1 oz). 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.
The Chimney Swift's wings are slender, curved and long, extending as much as 1.5 in (3.8 cm) 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 further 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 1.90–2.15 in (4.8–5.5 cm) in length. All ten of its tail feathers have shafts which extend as much as 0.5 in (1.3 cm) 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, has two fovea—small depressions in the retina where visual acuity is highest—in each eye. These help to make its vision especially acute. Like most vertebrates, it is able to focus both eyes at once; however, it is also able to focus a single eye independently.
Its bill is very small, with a culmen that measures a mere 5 mm (0.20 in) 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 looks very much like the closely related Vaux's Swift, but is slightly larger, with relatively longer wings and tail, slower wingbeats and a greater tendency to soar. It tends to be darker on the breast and rump than the Vaux's Swift, though there is some overlap in plumage coloring. It can be as much as 30 percent heavier than the Vaux's Swift, and its wings, which are proportionately narrower, show a pronounced bulge in the inner secondaries. The Chimney Swift is smaller, paler and shorter tailed than the Black Swift. In Central America, it is most similar to the 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 the more uniformly colored Chapman's Swift.
Range and habitat
A widespread breeding visitor to much of the eastern half of the United States (and barely into the southern reaches of eastern Canada), the Chimney Swift migrates to South America for the winter. It is a rare summer visitor to the western U.S, and has been recorded as a vagrant in Anguilla, Barbados, Greenland, Jamaica, Portugal, United Kingdom and the U.S. Virgin Islands. It is found over open country, savanna, wooded slopes and humid forest.
The Chimney Swift's wintering grounds were only discovered in 1944, when bands from birds banded (ringed) in North America were recovered in Peru. An indigenous Peruvian had been wearing the bands as a necklace.
Like all swifts, the Chimney Swift is a superb aerialist, and only rarely seen at rest. It is incapable of perching; instead, it clings to vertical surfaces.
The Chimney Swift is a gregarious species, and is seldom seen alone. It generally hunts in groups of two or three, migrates in loose flocks of 6–20, and (once the breeding season is over) sleeps in huge communal roosts of hundreds or thousands of birds.
The Chimney Swift is a monogamous breeder which normally mates for life, though a small percentage of birds change partners. Pairs perform display flights together, gliding with their wings upraised in a steep "V", and sometimes rocking from side to side. Returning birds arrive as early as mid March in the southern U.S., and as late as mid-May in the Canadian provinces.
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 in chimneys, with smaller numbers in airshafts, the dark corners of lightly used buildings, cisterns, or wells. The 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.
The female typically lays 4–5 eggs, though clutch sizes range from 3 to 6. The eggs, which are long and elliptical in shape, are moderately glossy, smooth and white, and measure 20 mm × 13 mm (0.79 in × 0.51 in). They are incubated by both parents, and hatch after 19 days. 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 4.6 years, but one is known to have lived more than 14 years. It was originally banded as an adult, and was recaptured in another banding operation some 12.5 years later.
Like all swifts, the Chimney Swift forages on the wing, feeding on flying insects. It generally flies quite high, though it descends during cold or rainy weather. When feeding, it regularly occurs in small groups, and sometimes hunts with swallows, particularly Barn Swallows and Purple Martins. It is an important predator of pest species such as the red imported fire ant and the clover root curculio.
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 migration is smaller than that of some passerines, suggesting that it must refuel en route at various stopover points.
The Chimney Swift has a twittering call, consisting of a rapid series of hard, high-pitched chips. It sometimes gives single chips.
Conservation status and threats
In 2010, the International Union for the Conservation of Nature changed the Chimney Swift's status from "Least Concern" to "Near Threatened". Although its population is estimated at 15 million, it has declined fairly precipitously over most of its range.
Their population may have increased historically with the introduction of large chimneys as nesting locations. With suitable man-made habitat becoming less common, their numbers are declining in some areas. In Canada, they were listed as Threatened by COSEWIC for several years with a likely future listing as a Schedule 1 species of the Species at Risk Act.
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 biting lice species Dennyus dubius. Its nest is known to host the Hemiptera species Cimexopsis nyctali, which is similar to the bedbug and can (on rare occasions) become a pest species in houses.
Severe storms, such as hurricanes, 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.
- 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.
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