Chimney swift (Chaetura pelagica)

Oct 22, 2017 Features / Columnists, Interesting Creatures in Guyana

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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 the Vaux’s swift and the 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 grey 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 4–5 white eggs. The altricial young hatch after 19 days and fledge a month later. The average chimney swift lives 4.6 years.
This is a medium-sized swift, measuring from 12 to 15 cm (4.7 to 5.9 in) in length, with a wingspan of 27 to 30 cm (11 to 12 in) and a weight ranging from 17 to 30 g (0.60 to 1.06 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 greyish 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 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 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.
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 to 2.15 in (4.8 to 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, this swift is bifoveal: each eye having both a temporal and a central fovea. These are small depressions in the retina where visual acuity is highest, and 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.
During the breeding season, at least half of the chimney swift’s forays occur within 0.5 km (0.3 mi) of its nest; however, it ranges up to 6 km (3.7 mi) 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 swallows, particularly barn swallows and purple martins; in mixed-species flocks, it is typically among the lower fliers. There is at least one record of a chimney swift attempting to steal a dragonfly from a purple martin, and it has been observed chasing other purple martins. In general, it is a diurnal 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 migration is smaller than that of some passerines, suggesting that it must refuel en route at various stopover points. [Source: Wikipedia]

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