Chimney Swift
Chaetura pelagicaOverview 1
A recognizable component of the eastern North American avifauna, this small, agile, fast-flying swift is easily identified by its characteristic "cigar on wings" profile. It breeds throughout much of southern Canada east of Saskatchewan, south through Texas and all states to the east, and is a newly established breeder (in small numbers) in southern California. In some locations, Chimney Swifts are most noticeable during migration, when flocks numbering in the thousands circle in large tornado-like flocks above roosting chimneys at dusk, and then suddenly descend in ever-narrowing vortices into their depths to spend the night.
While once probably thinly distributed across its breeding range, nesting in scattered hollow trees in old-growth forests, this swift increased dramatically with the arrival of European settlers and the multitude of nesting cavities provided by chimneys on their buildings. Over the past 20 years, however, Chimney Swift populations have been decreasing as old chimneys deteriorate and new ones are less suitable for nest sites.
Chimney Swifts spend winter months in the upper Amazon basin of Peru, Ecuador, Chile, and Brazil. We know little of the biology of these swifts while they are there. When they return to North America in March or April as flocks, pairs of birds soon break away to individual nest sites in chimneys or the walls of abandoned buildings. There the pair builds a nest of loosely woven twigs, cemented together and to the wall of the chimney with the bird's glue-like saliva. The female lays 4 or 5 eggs, which hatch in about 19¿20 days. It is not uncommon for an unmated helper to assist with the rearing of the young, which fledge in about 30 days. The relative importance of helpers to nesting success remains largely unstudied.
Large flocks of unmated birds commonly roost together in large chimneys throughout the summer, often leading to the misconception that the birds are nesting as a colony. Some of these flocks may even roost in a chimney occupied by a single nesting pair. When the young have fledged, small groups of parents and young from several chimneys move to larger staging chimneys in the area. At summer's end, they amass to migrate to South American wintering areas. In south-central Kansas, as many as 10,000 birds have been observed in one roosting flock.
Surprisingly, much of the life history of the Chimney Swift remains unknown, primarily because so much of this bird's day is spent in wide-ranging, fast flight and its nesting and roosting occur in dark, largely inaccessible chimneys and widely scattered tree cavities. Some important details of nest life of single pairs were observed in an artificial chimney in Iowa (Sherman 1952). Impressive long-term studies of breeding behavior, nesting biology, growth and development, survivorship, and fidelity to nest sites of many pairs were made in situations where nests were more readily accessible inside old buildings or where nesting sites were relatively close together on accessible rooftops (Dexter 1946 ¿ 1992, Fischer 1958, Cink in press a). Several studies have pieced together aspects of migratory pathways through the use of banding data (Calhoun and Dickinson 1942, Lowery 1943, Bowman 1952). Environmental influences on flocking, roosting, and feeding have been documented (Michael and Chao 1973, Zammuto and Franks 1978 ¿ 1981c). Some physiological discoveries on seasonal salivary-gland changes and use of torpor have been published (Johnston 1958, Ramsey 1970). Still, most observations were not continuous, the individual identities of all birds associated with nest sites or roosts were not known, and most young or nests were not followed long enough to document their fates. Thus, substantial gaps in our knowledge remain. Many studies are dated, with few new studies in the last 30 years.
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