Swifts

Swifts are the fastest fliers of all of the small birds , reaching speeds of 172-218 mph (275-349 kph), although 35-80 mph (56-128 kph) is more common. They belong to the family Apodidae, a name meaning "without feet" and a reference to the fact that a swift in flight appears to have no legs or feet. Indeed, the legs of swifts are small and weak so that a swift that lands on the ground may have difficulty taking off again.

Swifts gather food, drink, bathe, court, and mate all while on the wing. They are more closely related to the hummingbirds than to the swallows, which they resemble. There are about 80 species of swifts, and they are found throughout the world except in the Arctic and Antarctic. Swifts are generally small birds, ranging from the size of a sparrow to the size of a small hawk. They are generally gray or brown, although some species are marked with white.

The wings of swifts are slender and pointed, the ideal shape for a rapid flier. The tail contains 10 feathers, and may be forked or short and stiff. Although their legs are weak, swifts' claws are strong and ideally suited to clinging to chimneys or rock walls on which they roost. The bill of swifts is tiny, but the gape is large, and well-suited for catching insects while in flight. Among the insects eaten by swifts are spiders, aphids , ants , bees , wasps , midges, mayflies , beetles , and termites . One Alpine swift was found to have a ball (called a bolus) of 600 insects in its throat, which it was taking back to feed its young.

Swifts can be distinguished from the superficially-similar swallows by their style of flight. Swifts alternate a short glide with a series of shallow, rapid wingbeats, and in flight can be mistaken for bats . Swallows, on the other hand, are more fluid fliers. It was thought that swifts alternated their wing beats in flight—using first the left then the right, but stroboscopic studies have confirmed that the wings in fact beat in unison (if jerkily) because of the swifts' short, massive wing bones.

Not only are swifts rapid flyers, but they also have great endurance. One bird was estimated to have flown more than million miles in its nine-year life span. Since swifts are long-lived birds (some have been known to live for nearly 20 years), it is not unreasonable to assume that some individuals may have flown far more miles than that. Swifts migrate seasonally with species from North America generally wintering in South America . However, one North American species, the white-throated swift, becomes torpid during periods of cold weather , much like its relative the hummingbird.

Swifts are gregarious. A large colony of chimney swifts nested in an air shaft at Kent State University in Ohio. When chimney swifts prepare to roost for the night, a flock will circle about a chimney for as long as an hour. The bird closest to the chimney will be the first to enter, and the rest follow, looking like a puff of smoke going down the chimney.

Nesting is usually a solitary affair. Swifts are loyal to both their traditional nesting site and to their mate. The male and female gather twigs for the nest by grabbing the twig while in flight; if it breaks off, the bird adds it to the nest. Nests are cup-shaped agglomerations of twigs, mud, moss , and saliva (building materials vary by species), usually in a spot secluded and inaccessible to predators, such as a crevice in a high cliff face. Because the birds need so much saliva during breeding season, their salivary glands increase in size accordingly, swelling to as much as 12 times the normal size.

The glutaneous saliva is considered by some people a delicacy. In Southeast Asia , swift nests are harvested for use in bird's-nest soup, which some believe keeps people young. The nests of these Asian species are constructed entirely of fast-drying saliva. Some swift species have become rare because of the harvesting of the nests. And, predictably, as the nests have become more rare, they have become more expensive, commanding as much as $1,000 per pound. The escalating price has not reduced demand, and nest collectors are traveling farther afield in China, Thailand, Vietnam, and other Asian countries in search of nests.

Depending on her species, the female lays between one and six white eggs. Both the male and female incubate the eggs, which hatch 17-28 days after being laid. The young swifts fledge at about 30 days old.

The chimney swift (Chaetura pelagica) is the only North American species generally found east of the Mississippi River. Other species include Vaux's swift (Chaetura vauxi), the smallest North American species, which weights just 0.66 oz (18.9 g), and the black swift (Cypseloides niger), the largest North American swift, which is rarely seen because of its high mountain habitat . The swift is not a songbird, and its voice consists of high, piercing screams.