Medium-sized swallow, tail not sharply forked. Total length, tip of bill to tip of longest tail feather is about 14.0 cm. Bicolor. Mostly steely greenish blue above, white below. Upperside body feathers either iridescent greenish blue (males and older females) or mixture of brown and greenish blue. A highly social bird. Outside the breeding season, it often forms large flocks, up to several hundred thousand birds at some nighttime roosts (Robertson et al. 1992).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.
Western Hemisphere Range
In the Bozeman area, normal migration periods are from April 9 to May 15 and August 10 to September 1.
Open fields, meadows, marshes, beaver ponds, lakeshores and other wetland margins. Uses trees only for nesting and occasional roosting (Robertson et al. 1992).
Mostly flying insects, though vegetable matter is eaten during unfavorable weather conditions. Forage over open water, marshes, ponds, and fields, as well as in shrubby habitat (Robertson et al. 1992).
Usually one brood per year. A hole nester. It depends on woodpeckers and other species that excavate and abandon cavities in dead trees (typically along beaver ponds and wetland margins) and to a lesser extent on nest boxes. Mean clutch size 5.46. (Robertson et al. 1992). Near Fortine, egg dates are May 15 to June 12. Young left the nest June 23 to July 10. Statewide, incubation is usually in late June and early July.