Nests singly or in small colony. Clutch size is 3-7 (usually 4-7). Incubation lasts 18-20 days (Stiles and Skutch 1989; Baicich and Harrison 1997). Young leave nest after 20-21 days; will perch on interior wall the nest is built on, but may not fly freely for up to another 7 days (Baldwin and Zaczkowski 1963). At least some birds nest at one year of age (Bull and Collins 1996). Will return to same nest site (Baldwin and Zaczkowski 1963; Bull and Collins 1996). In an Oregon study, 70% of 46 nest trees were re-used in subsequent years, and nest site fidelity was also high, with 14 of 15 marked birds recaptured at the same nest tree (Bull and Collins 1996).