During the nonbreeding season, passerine birds may spend more than half their day roosting (Skutch 1989). Nocturnal roost sites are potentially important resources, serving primarily to reduce risk of predation and reduce costs associated with energetic and physiological constraints during inactive periods (Walsberg 1986, Skutch 1989) . Vulnerability and low nighttime temperatures during winter are probably strong selective forces in avian life history; a safe roost site increases a bird's chances of survival in the same way that a safe nest site increases chances of fledging. Despite this apparent importance, little is known of intra- and interspecific patterns of passerine roosting behavior.