Roosting behavior and group territoriality in American Crows

Cooperative groups of American Crows (Corvus brachyrhynchos) maintain group territories year-round while often traveling long distances to roost communally at night. Our goal was to discover how territorial crows resolve the conflict between the cohesive nature of group behavior with requirements of dispersal to roost communally. We color-marked crows to study group composition over true years, and radio-tagged crows to study movement among roosts, territories, and feeding areas. Most crows showed diurnal fidelity to the group territory throughout the year. Yet, most birds frequently left territories during the day to forage up to 4 km away. At night, crows roosted either on their territory or 18 km away at a large roost adjacent to a landfill. Crows roosted on territories more often in spring (87%) than in winter (42%). Group cohesion was high on territories, yet we found no evidence for group behavior away from territories. Crows arrived singly both to territories in the morning and to the communal roost in the afternoon. Group cohesion for territorial crows appears to be based on decisions of individuals to return to territories from distant roosting and foraging sites. Group cohesion on territories is tied to retention of breeding sites, whereas dispersal for communal roosting likely is linked to benefits derived from foraging away from territories, particularly in winter when physiological stress is greatest and territorial food supplies are lowest.