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How the Chimney Swift, Chaetura pelagica, roosts, nests, and eats
© Rosemary Drisdelle
JUli 5,2014
North American chimneys east of the Rockies are often occupied by roosting flocks of Chimney Swifts. These birds are also tireless fliers-masters of the air.
Bird or bat?
The sun is setting in a clear summer sky when your eye is drawn skyward by an odd twittering sound. Even stranger, you observe a gathering of some flying creatures wheeling above an old brick chimney. Around and around they circle, with a few individuals dipping suddenly toward the chimney top then returning to the rest. Their darting dipping movement and the twittering sound reminds you of bats, but something is wrong: bats emerge at dusk and fly away—these flyers seem to be congregating. Then, one or two drop abruptly into the chimney, and soon the whole wheeling darting flock spirals suddenly into the chimney like a small tornado being sucked down a manhole; like something out of Harry Potter. Now the air is empty and silent. What have you seen? They’re not bats, and they’re not chimney sweep birds, they’re Chimney Swifts, Chaetura pelagica.
Chimney Swifts
The Chimney Swift, sometimes called the American Swift (the similarity of chimney swift to chimney sweep no doubt accounts for another common name—chimney sweep birds), spends its days on the wing hunting insects, and nights clinging to vertical inner walls of hollow trees, chimneys, abandoned buildings and old stone wells. Before Europeans colonized North America and removed many of the old hollow trees, Chimney Swifts roosted almost exclusively in trees. They adapted readily to chimneys, however, and actually increased in numbers.
Chimney Swifts are migratory birds, spending their winters in Peru and the Amazon Basin. They appear in North America in early spring, and nest in May, with each pair raising three to five chicks. Young birds fledge by about the thirtieth day and join their parents in flight. In the fall, young and old congregate in large numbers and as soon as the weather turns cold and flying insects start to decrease, they are gone.
Interesting facts about Chimney Swifts
Chaetura pelagica is a fascinating bird. Here are some interesting facts about Chimney Swifts:
• A Chimney Swift can eat a third of its weight in insects every day. Many annoying and biting insect pests are removed from our environment by these voracious birds.
• Chimney Swifts do not perch or walk on the ground: their feet are designed for clinging to vertical surfaces. From the time they exit the chimney to the time they reenter it, they never land.
• The tail feathers of Chimney Swifts are tipped with stiff bristles, which help them stay in place while clinging to a vertical surface.
• Chimney Swifts have to do everything while in flight—catch flying insects, grab airborne nesting materials, and break twigs off trees for nest building.
• The nest is built mostly of twigs, glued to each other and to a vertical wall with saliva. While building, the bird’s salivary gland greatly enlarges to meet the demand.
• There is usually only one active nest in any one chimney or tree—thus, the funnel of birds you see entering the chimney are roosting, not nesting there.
• Some flocks of migrating birds contain both swifts and swallows.
The Chimney Swift is apparently declining once again, partly due to the disappearance of many old chimneys. To help conserve Chaetura pelagica, some people are preserving old brick chimneys, saving them from demolition, or building chimney-like structures where Chimney Swifts can roost and nest.
