White-throated Swifts are among the most accomplished fliers of all North American birds, streaking forward at high speed, then suddenly changing direction with lightning-fast adjustments of wing and tail. The generic name of this species is particularly apt: Aeronautes, or "sky sailor." Identified by its chattering staccato call, black-and-white coloration, and characteristic rapid, erratic flight, it is a familiar sight during summer months in the canyons, foothills, mountains¿and, increasingly the cities¿of the western United States.
The White-throated Swift breeds from the southern interior of British Columbia south to Mexico and Honduras, nesting in high cliffs and bluffs of this rugged country-side. By the mid-1900s it had begun to exploit holes and crevices of buildings, bridges, and highway overpasses for roosting and nesting. Resident from the southwestern United States south, migrants move northward from April to October to take advantage of numerous potential nesting areas and abundant aerial insects of the temperate summer.
Its nest is a simple cup constructed from materials gathered on the wing, stuck together with gluelike saliva. Remarkably little is known about the reproductive biology of the species. Early collectors used dynamite to obtain the first nests and eggs. The species exhibits a high degree of site tenacity; some sites have been attended by flocks for over 50 years. Populations appear stable, although it is unknown what effect pesticides, recreational rock-climbing, and increasing use of human-made structures for nesting sites may have on individual breeding success and survival.
These swifts spend their days on the wing foraging on "aerial plankton" and chasing one another, returning to roost in the evening. Their morning exit and evening entry times are governed by local climatic conditions. In evening they gather above a roost, ascending beyond view and then, at some unknown cue, descend as a group. First, the observer hears the wind in their wings, then a swirling in front of the roost crack; individuals enter the roost several abreast. Occasionally one misses, bouncing off the entrance to rejoin the swirling mass. The entire group disappears inside within minutes.
A highly social creature, this swift forages in groups; during the breeding season, chases intensify into spectacular Courtship Falls: Two individuals cling together, pinwheeling several hundred feet before releasing just above the ground.
Despite its spectacular behavior and affinity for human-made structures, little is known of the life history of this species. Awaiting discovery include basics such as intra-familial relationships, migratory behavior and routes, range of vocalizations, nest-site selection, reproductive parameters and success, causes of mortality, and population dynamics.
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