They can be very aggressive to other birds and mammals. Apparently, this group unity imposes demands of regimentation, as ill, injured and old crows are driven from the flock and often killed. Perhaps, because crows function as a group and the safety of the group depends in large measure upon unity and conformity within the group, it becomes important that all function together. Flocks of crows often roost together during the night and then separate to feed during the day. Some birds will visit the same areas each day to feed while others have no apparent routine.
Crows often post sentinels while they feed to alert each other to impending dangers.
American crows are partially migratory. In many colder areas of the country, crows will migrate south seasonally. In Connecticut, most crows will remain throughout the winter. Commonly, crow roosts are found in stands of mature trees and can be located near homes, buildings, walkways and parking lots. Fecal droppings can accumulate under a crow roost, presenting a health hazard and nuisance by covering cars, walkways and other objects.