Vaux's Swift, a slightly smaller counterpart of the Chimney Swift (Chaetura pelagica) of eastern North America, breeds from just south of the Yukon through the western United States to Mexico, Central America, with a disputed subspecies in northern Venezuela. During winter months, northern migrant populations of this species overlap southern residents. Best known for its quick flight and dazzling aerial agility, this bird seldom perches except when nesting or roosting, and it probably mates on the wing. Hollow trees and unlined chimneys are its favored nesting and roosting sites, making the Vaux's Swift vulnerable to loss of old-growth forest and aging masonry structures. Indeed, recent declines in Vaux's Swift populations have been documented throughout its range where mature forest is dwindling. Its nest, an open half-circle of loosely woven twigs, is glued together and attached to the inside of a hollow tree or chimney with sticky saliva. In migration, large flocks of this species circle roosts at dusk, feigning entry until the first few birds take the plunge—then the whole flock follows abruptly, literally pouring out of the sky and disappearing into the roost.
Like other swifts, the Vaux's Swift is almost entirely insectivorous—a consumer of aerial plankton—hawking a variety of ants, bugs, flies, moths, spiders, and aphids from the air. An adult feeding young collects boluses of food in its mouth and carries these back to its nestlings. Each parent makes up to 50 trips per day, delivering more than 5,000 small insects from dawn to dusk.
This swift is named for William S. Vaux (1811–1882), a member of the Academy of Natural Sciences of Philadelphia and a friend of John K. Townsend, who described this species in 1839 from specimens collected on the Columbia River.
Many of the life history traits of the Vaux's Swift remain poorly known, although extensive studies in forests of northeastern Oregon have provided information on nest and roost site characteristics (1, 2, 3), diet and foraging activity (4), and nesting chronology (5). Comparative studies in other parts of its range are desirable.