Vaux's Swift, a slightly smaller counterpart of the eastern North American Chimney Swift (Chaetura pelagica), breeds from southwestern Canada through the western United States to Mexico, Central America, and northern Venezuela. In winter, 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 are its favored nesting and roosting sites (chimneys are used on occasion), making this swift vulnerable to loss of old-growth forest. Indeed, recent declines in Vaux's Swift populations have been documented in the Pacific Northwest where mature forest is dwindling. Its nest, an open half-circle of loosely woven twigs, is glued together and to the inside of a hollow tree or chimney with the bird's 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 tree.
Like other swifts, the Vaux's is almost entirely insectivorous-a strainer 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 this species are still unknown, although extensive studies in forests of ne. Oregon have provided information on nest and roost site characteristics ( Bull and Cooper 1991 ; Bull and Blumton 1997 ; Bull 2003b ), diet and foraging activity ( Bull and Beckwith 1993 ), and nesting chronology ( Bull and Collins 1993a ). Comparative studies in other parts of its range are desirable.