Forages and migrates during day. May enter torpor in periods of cold weather (Terres 1980). Number of birds at two tree roosts monitored in northeastern Oregon ranged from 9 to 479, with highest counts in spring (Bull 1991). During migration can gather in very large roosting flocks; up to 40,000 regularly roost in one large chimney in Portland (Eshbaugh 2000), and other large chimney roosts occur in a variety of Oregon cities (Bull 2000) and in Los Angeles, California.