The Chimney Swift ( Chaetura pelagica ) is a familiar component of the eastern North American avifauna. This small, agile, fast-flying aerial insectivore is easily identified by its characteristic “cigar on wings” profile. Chimney Swifts are among the most aerial of birds, spending the majority of their lives in the air, only stopping to roost or to nest. Because of the height at which they feed above the ground, the mechanics and ecology of foraging is just beginning to be studied.
Physical Characteristics and Habitat
Chimney Swifts are small birds with slender bodies and very long, narrow, curved wings. When observed overhead, passing swifts are frequently described as resembling “flying cigars,” a visual analogy attributable to the birds’ five-inch-long, tube-shaped bodies, comparatively long, narrow wings, and muted grey-brown plumage. They have small round heads, short necks, and short, tapered bills. They can grow to sizes of 5.9 inches in length with an 11.8 inch wingspan and can weigh up to 1.1 ounces. Chimney Swifts are generally a dark grayish to brownish-gray, sooty color. Males and females look alike.
Chimney Swifts breed in urban and suburban habitats across the eastern half of the United States and southern Canada. Our region is part of the species’ summer range, an enormous portion of eastern North America stretching from the Gulf Coast to just north of the Great Lakes. They are most common in areas with a large concentration of chimneys for nest sites and roosts. In rural areas, they may still nest in hollow trees, tree cavities, or caves. Chimney Swifts forage mostly over open terrain but also over forests, ponds, and residential areas. During migration they forage in flocks over forests and open areas and roost in chimneys at night. They spend the winter in the upper Amazon basin of Peru, Ecuador, Chile, and Brazil, where they are found in open terrain and on roosts in chimneys, churches, and caves.
Chimney Swifts are incapable of perching like most birds. Instead, they cling to vertical surfaces with their feet, and use the stiff shafts that protrude from the ends of their tail feathers as a brace. Chimney Swifts have specially designed feet that enable them to cling to vertical surfaces.
Dietary Habits
Chimney Swifts eat entirely in flight, dining on numerous species of flies, beetles, termites, flying ants, bees, wasps, and moths. The birds’ aerial maneuvers are a mix of rapid wing beats and dynamic glides, and much of the action relates to feeding. Chimney Swifts eat on the wing, using their unusually large mouths to capture up to 5,000 flying insects per day. Chimney swifts feed exclusively while in flight. They take a variety of insect and spider prey. Chimney Swifts feed on flying insects including flies, mosquitos, beetles, wasps, bees, and other insects. They grab large insects with their bills; small ones go right down the throat.
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Chimney Swifts feed over urban and residential neighborhoods, fields, grasslands, shrublands, orchards, forests, and marshes, usually some distance away from nest sites. They can also pick insects from branch tips and “helicopter” down through the foliage to flush out prey. Normally diurnal foragers, they sometimes hunt for insects at night around streetlights or lit windows. They have been reported taking berries from elderberry bushes.
Foraging Behavior
Chimney Swifts feed in open fields, forests, or shrublands, usually away from their nest sites. They are noted for their ability to flush out insects by flying low and using the air pressure from concentrated downdrafts to disturb potential prey. Typically seen foraging in small flocks, Chimney Swifts forage in the sky over any kind of terrain, wherever there are flying insects.
Nesting Behavior
The architectural reference in the species’ common name alludes to commensalism involving birds and people that dates to the European settlement of eastern North America. As a biology term, commensalism denotes situations in which one species obtains benefits from another, without harming or benefiting the provider. Historic records indicate that before colonial times the species now known to science as Chaetura pelagica used hollow trees for roosting and nesting. Within hollow trees and chimneys, sheltered interior walls meet the birds’ requirements for nesting and roosting.
Although they originally nested in natural sites such as caves and hollow trees of old-growth forests, Chimney Swifts now nest primarily in chimneys and other artificial sites with vertical surfaces and low light (including air vents, old wells, abandoned cisterns, outhouses, boathouses, garages, silos, barns, lighthouses, and firewood sheds).
Chimney Swifts perform aerial courtship displays within 2 weeks of arriving to their North American breeding grounds. In one of the best known displays, two birds fly close together, calling; first the rear bird and then the leader snaps its wings into a V-shape and the two glide together in a downward curve. Both members of a breeding pair may fly toward several potential nest locations, then cling side by side at one particular site, with one member of the pair giving a rhythmic chipping call.
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The nest is a half-saucer of loosely woven twigs, stuck together and cemented to the chimney wall with the bird’s glue-like saliva. Both parents independently contribute to the nest: they break off small twigs with their feet while flying through branches, then return to the nest site with the twigs in their bills. The completed nest measures 2-3 inches from front to back, 4 inches wide, and 1 inch deep. Nests are built into a half saucer shape from loosely woven twigs. The nests are attached to vertical surfaces with the birds glue-like saliva. Both parents contribute to the construction of the nest. Nests, on average, measure 2-3 inches long, 4 inches wide, and an inch deep.
Females normally lay 3-5 white eggs that are incubated by alternating adults for 18-19 days. After hatching, both parents alternate catching insects for their young. Hatchlings are pink and completely naked at birth with sharp claws that enable them to cling to textured surfaces. Within a few days, black pin feathers begin to appear. Once they are 8-10 days of age, the nestling’s feathers begin to unfurl. By 15-17 days of age, their eyes begin to open and most of the flight and body feathers will be unfurled. Close to a month after hatching, young Chimney Swifts will leave the nest for their first flight.
Social Behavior
Solitary birds will roost together in large flocks. Often, an unmated individual may assist a breeding pair with rearing the young. After the breeding season, Chimney Swifts join larger flocks to migrate to South America. During migration, as many as 10,000 swifts may circle in a tornado-like flock at dusk and funnel into a roosting colony to spend the night. Unmated birds roost together in large flocks, sometimes even in a chimney occupied by a nesting pair. Often an unmated helper may assist a breeding pair with rearing the young, behavior called extra-parental cooperation or cooperative breeding.
Conservation Status
The 2025 State of the Birds report lists Chimney Swift as an Orange Alert Tipping Point species, meaning that it has lost more than 50% of its population in the past 50 years and has shown accelerated declines within the past decade. According to the North American Breeding Bird Survey, this species declined by an estimated 2.3% per year between 1966 and 2023, resulting in a cumulative decline of 74% over that period. Numerous environmental pressures have precipitated long-term population reductions of many insect species. Population declines in aerially foraging insectivorous birds have also been detected.
Chimney Swifts probably became much more numerous with European settlement and the building of millions of chimneys. But traditional brick chimneys are now deteriorating, and modern chimneys tend to be unsuitable for nest sites. Adding to the problem, some homeowners now cap their unused chimneys. Chimney cleaning during the nesting season can inadvertently destroy nests and kill swifts. Logging of old-growth forests can reduce the availability of natural nest sites.
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The Chimney Swift Conservation Program, through the Maryland Bird Conservation Partnership, seeks to assess local Chimney Swift populations as well as increase nesting areas for local birds. To help local Chimney Swifts, consider helping with the program through reporting active chimney/tower sites, providing homes for Chimney Swifts, and/or volunteering for the program. The Audubon Society of Western Pennsylvania (ASWP) launched a regional initiative to publicize the species’ plight and address reductions in Chimney Swift nesting and roosting habitat. The 106-year-old conservation organization has since led a broad coalition of partners in an ongoing effort to construct, install, and monitor more than 150 Chimney Swift towers at appropriate locations in southwestern Pennsylvania.