Comments: Found in mature forests but also forages and migrates over open country (Tropical to Temperate zone) (AOU 1983; Bull and Collins 1993). Forages over land and water. Often roosts in large flocks in hollow trees or chimneys just prior to and during migration (Bull and Blumton 1997, Eshbaugh 2000).
BREEDING: In North America, prefers late seral stages of coniferous and mixed deciduous/coniferous forests; more abundant in old-growth forests than in younger stands (Manuwal and Huff 1987, Gilbert and Allwine 1991, Huff and Raley 1991, Lundquist and Mariani 1991; Manuwal 1991; Bull and Collins 1993). In Washington, found more abundant in old-growth (> 250 years old) than in younger (< 165 years old) forest stands (Manuwal and Huff 1987), and more abundant in wet old-growth than mesic or dry old-growth (Manuwal 1991). In the southern Washington Cascade Mountains, abundance was positively correlated with high density of live trees >100 cm in diameter at breast height (mainly Douglas-fir [Pseudotsuga menziesii], Western Hemlock [Tsuga heterophylla], and Western Redcedar [Thuja plicata]) and with large snags (Douglas-fir and Western Hemlock; Lundquist and Mariani 1991). The multi-layered broken overstory of old-growth forests may also provide easier access to aerial insects than closed, continuous canopies of younger forests (Lundquist and Mariani 1991). In northern California, uses Douglas-fir forests but highest densities are in coastal redwood (Sequoia sempervirens) habitats (Sterling and Paton 1996; CDFG 2000).
BREEDING AND WINTERING: In the neotropics, found in mixed coniferous-broadleaf, deciduous broadleaf, and broadleaf evergreen forests (Rappole et al. 1995). In Mexico, breeds in highlands, ranging into lowlands in migration or winter; although a disjunct population is resident on the Yucatan Peninsula (Howell and Webb 1995). In Honduras, common in humid Caribbean lowlands to interior highlands up to 2000m; one breeding record in cloud forest; flock also recorded feeding around a large almendro tree (Dipteryx oleifera) in an open field (Monroe 1968). In Costa Rica, resident in highlands (700-2000 m), occasionally ranging higher or into lowlands (Stiles and Skutch 1989).
NEST SITES: Nests are usually in large-diameter hollow trees, broken-top trees, or stumps; also in chimneys. Nest is a saucer-shaped structure of twigs and spruce or pine needles glued to interior vertical wall of hollow tree, stump, chimney, dark attic, or similar dark cranny. Usually locates nest near bottom of cavity (Baicich and Harrison 1997; Bull and Collins 1993).
In Oregon, nests have been recorded in live or dead Grand Fir (Abies grandis) and Bigleaf Maple (Acer macrophyllum) with hollow chambers where heartwood had decayed (Bull and Cooper 1991; Bull and Collins 1993). For 21 nests located in a northeastern Oregon study, nest trees averaged 67.5 cm diameter at breast height (range 45-96 cm) and 25 m tall (range 15-37 m), and usually occurred in old-growth forest with an average canopy closure of 71%. All of these nests were in trees hollowed out by Indian paint fungus (ECHINODONTIUM TINCTORUM) and with an entrance hole excavated by Pileated Woodpeckers (Bull and Cooper 1991). In Washington, one nest recorded in a broken-topped Western Redcedar (Thuja plicata) 10 m tall and 76 cm diameter at breast height in old-growth forest (Lundquist and Mariani 1991). In Montana, three nests recorded in old broken-topped Western Hemlock (Tsuga heterophylla; Baldwin and Zaczkowski 1963). Less typical records in cottonwood (POPULUS spp.) and sycamore (Platanus spp.; Taylor 1905). In British Columbia, the only confirmed tree nest was in a hollow Bigleaf Maple; there are several other records of birds seen entering or leaving Western Redcedars and Black Cottonwoods (Populus trichocarpa), but nesting was not confirmed (Campbell et al. 1990, M. G. Shepard, pers. comm.).
ROOSTS: Two roosts were recorded in northeastern Oregon, both in Grand Fir trees 200-300 years old, > 100 cm diameter at breast height in old-growth forest stands (Bull 1991). Postfledging swifts in Oregon roosted in the nest tree (44% of juveniles, 64% of adults) or in trees up to 9.2 kilometers away. Roost trees were hollow, live or dead grand firs (94%) or ponderosa pines (6%), with an average DBH of 77 cm and an average height of 26 m (Bull and Blumton 1997). One record of birds roosting in the open: in southern California a large tight cluster was found on the trunk of a tamarisk tree (Tamarix spp.; Stager 1965). In Oregon, the largest migratory roost (15,000 to 40,000 birds) is in a large brick chimney at a school in Portland (Eshbaugh 2000).