White-throated Swift Life History

Habitat

Habitat Scrub

White-throated Swifts nest in mountainous and hilly areas, where they forage above forests, meadows, canyons, cliffs, and pinnacles. For nesting, they require crevices in cliffs, but they have adapted to human-modified environments and also nest in highway overpasses, quarries, buildings, and bridges. They nest from very low elevations, such as Death Valley (180 feet below sea level), up to well over 11,000 feet in elevation. The terrestrial habitat in nesting areas varies from grasslands to shrubsteppe to forests; nest sites and access to insect prey appear to be more important for nesting than terrestrial habitat itself. They readily nest on islands offshore. When foraging, White-throated Swifts may travel great distances from the nest, and during migration they may turn up just about anywhere, from the coast to the high peaks. Like many other swift species, they visit lakes and ponds to drink water early in the morning or late in the afternoon.

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Food

Food Insects

White-throated Swifts eat insects and spiders, which they capture in the mouth while flying. Their flight is dizzyingly rapid, twisting, and acrobatic, and they often turn sharply to sweep back through a particularly insect-rich part of the air column. They forage both singly and in groups of a few dozen (sometimes up to hundreds or rarely thousands of individuals). They often hunt in places where rising air concentrates insects, such as along canyons or cliffs, but they also hunt along the leading edges of storms. Prey includes many types of flies, weevils, hister beetles, leaf beetles, rove beetles, skin beetles, flower beetles, stinkbugs, treehoppers, leafhoppers, squash bugs, bees, wasps, and flying ants.

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Nesting

Nest Placement

Nest Cliff

Male and female visit potential nest sites together. The nest is set in crevices in rocky terrain, usually a vertical surface such as a canyon wall or cliff but sometimes a human-made structure, usually higher than 20 feet above the ground. Occasionally, they take over disused nests of other bird species.

Nest Description

The nest is a shallow cup made of feathers, grasses, mosses, plant down, and bark that at least one of the pair collects in flight and glues together with sticky saliva. Nests vary greatly in dimensions, probably based on the shape of the nest cavity. Average measurements are about 5 inches across and 2 inches tall, with a shallow interior cup about 3 inches across and 1 inch deep.

Nesting Facts

Egg Description:

White

Condition at Hatching:

Naked and helpless.

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Behavior

Behavior Aerial Forager

As they return to nesting areas in spring, White-throated Swifts immediately commence aerial courtship in pairs or small groups, chasing each other through the skies near nesting cliffs, calling frequently. In pairs, one will chase another, which raises the wings into a V-shape for several seconds. Sometimes the following bird then overtakes and clings to the back of the other in flight, and the two then plummet hundreds of feet toward earth. Whether this is only a form of courtship, or involves mating, is unknown. Male and female sometimes mate at the nest crevice. White-throated Swifts do not appear territorial; pairs often nest close together, almost in a colony, and are highly social year-round. Both adults feed the nestlings. During the nesting season, White-throated Swifts form small flocks that often depart the nest area to forage together, calling to each other as they gather and also on their return to the nest area. After the young fledge, larger flocks gather for communal roosting (including dozens to hundreds of birds).

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Conservation

Conservation Low Concern

White-throated Swift numbers are hard to track with precision. The North American Breeding Bird Survey indicates a possible decline of about 1.7% per year between 1968 and 2015, but notes considerable uncertainty about this trend. If this estimate is correct, it would correspond to a cumulative decline of 56% over that period. A 2016 Partners in Flight report estimates a 48% decline since 1970. Partners in Flight estimates the global breeding population at 3.2 million and ranks the species a 10 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. The reasons for the decline of this species are not known, but it fits an overall pattern of widespread declines in many species of aerial insectivores. It is possible that pesticides, which reduce prey and are potentially lethal to birds, could be involved in declines.

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Credits

Lutmerding, J. A. and A. S. Love. (2019). Longevity records of North American birds. Version 1019 Patuxent Wildlife Research Center, Bird Banding Laboratory 2019.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Rosenberg, K. V., J. A. Kennedy, R. Dettmers, R. P. Ford, D. Reynolds, J. D. Alexander, C. J. Beardmore, P. J. Blancher, R. E. Bogart, G. S. Butcher, A. F. Camfield, A. Couturier, D. W. Demarest, W. E. Easton, J. J. Giocomo, R. H. Keller, A. E. Mini, A. O. Panjabi, D. N. Pashley, T. D. Rich, J. M. Ruth, H. Stabins, J. Stanton, and T. Will (2016). Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee.

Ryan, Thomas P. and Charles T. Collins. (2000). White-throated Swift (Aeronautes saxatalis), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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