About Chaetura pelagica (Linnaeus, 1758)
This description covers the species Chaetura pelagica, commonly known as the chimney swift, a medium-sized swift. It measures 12 to 15 cm (4.7 to 5.9 in) in length, with a 27 to 30 cm (11 to 12 in) wingspan, and weighs 17 to 30 g (0.60 to 1.06 oz). Males and females have identical plumage, though males on average are slightly heavier than females. Adult plumage is dark sooty olive on the upperparts and grayish brown on the underparts, with a slightly paler rump and uppertail covert feathers, and a noticeably paler throat. Among all Chaetura swifts, this species has the most uniformly colored upperparts, with very little contrast between the back and rump. Its beak, feet, and legs are all black, and its iris is dark brown. Juvenile plumage, which young birds keep for their first few months after fledging, is very similar to adult plumage, differing only by having whitish tips on the outer webs of the secondaries and tertials. The chimney swift has long, slender, curved wings that extend up to 1.5 in (3.8 cm) past the bird's tail when folded. Its pointed wingtips reduce air turbulence and thus drag during flight. The humerus (the inner wing bone) is quite short, while the more distal bones further along the wing are elongated; this combination lets the bird flap very quickly. In flight, the chimney swift holds its wings stiffly, alternating between rapid, quivering flaps and longer glides. Its flight shape is widely described as "a cigar with wings," a description first coined by Roger Tory Peterson. While the bird often looks like it beats its wings asynchronously during flight, photographic and stroboscopic studies have confirmed it beats them in unison. The illusion of asynchronous beating comes from its very fast, highly erratic flight that includes many rapid direction changes. Like all swifts, the chimney swift has very short legs. Its feet are small but strong, with very short toes tipped with sharp, curved claws. Its toes are anisodactyl (three facing forward, one facing back) like most birds, but the chimney swift can swivel its back toe (the hallux) forward to get a better grip. Unlike the legs and feet of most birds, the chimney swift's legs and feet have no scales and are instead covered in smooth skin. Its tail is short and square, measuring only 4.8 to 5.5 cm (1.90 to 2.15 in) in length. All ten of its tail feathers have shafts that extend up to 1.3 cm (0.5 in) beyond the feather vanes, ending in sharp, stiff points that help the bird prop itself against vertical surfaces. The chimney swift has large, deep-set eyes, each protected by a small patch of coarse, black, bristly feathers in front of the eye. The swift can adjust the angle of these feathers, which may help reduce glare. It is far-sighted, and like some birds of prey, it is bifoveal: each eye has both a temporal and a central fovea. These small retinal depressions are where visual acuity is highest, and they make the chimney swift's vision especially sharp. Like most vertebrates, it can focus both eyes at the same time, but it can also focus a single eye independently. Its bill is very small, with a culmen that measures only 5 mm (0.20 in) long. However, its gape is very large, 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 is a widespread breeding visitor to most of the eastern half of the United States and the southern portions of eastern Canada. It migrates to South America to spend the winter. It is a rare summer visitor to the western United States, and has been recorded as a vagrant in Anguilla, Barbados, Greenland, Jamaica, Portugal, the United Kingdom, and the U.S. Virgin Islands. It can be found over open country, savanna, wooded slopes, and humid forests. The chimney swift's wintering grounds were not discovered until 1944, when bands from North American banded (ringed) birds were recovered in Peru. An indigenous Peruvian person had been wearing the bands as a necklace.
