They feed on the bark, cambium, twigs, leaves, and roots of deciduous trees and shrubs, such as willow, alder, birch, and aspen, and on various parts of aquatic plants, especially the young shoots of water lilies. Beavers anchor sticks and logs underwater to feed on during winter. Beaver populations are divided into colonies usually comprising four to eight related individuals, generally a mated pair of adults and the young of 2 years. Beavers apparently are monogamous, there usually being only a single breeding female in a colony. In favorable areas there may be as many as 3 colonies per sq km, but more typical density is 0.4-0.8 colonies per sq km.
Females appear to be dominant over both males and young, at least at certain times.
The members of a beaver colony generally get along amiably with one another, often working together to build dams. Both sexes display territorial behavior and will threaten and fight intruding beavers. Communication is through postures, scent marking, tail slapping, and several vocalizations, including a whistling or whining call. There is a single annual breeding season, with mating usually taking place about January or February and births occurring from April to June. The estrous cycle lasts about 2 weeks, during which females are receptive for 10-12 hours.