Natural resource managers faced with resolving beaver damage may make decisions based on classic literature suggesting that beavers (Castor canadensis) are monogamous breeders that live in colonies composed of a breeding pair of adults, their offspring, and occasionally the offspring from the previous year; and that beavers typically breed during the winter months and bear their offspring in the spring. We analyzed colony composition at 89 damage sites in seven southeastern states and found deviations from these classic studies. Colony size ranged from 2 to 18 individuals (χ = 5.66, SE = 0.36). Eleven colonies contained one male and one female only, yet only five of those were breeding pairs. Colonies contained from 1 to 11 males, whereas the number of females among colonies ranged from 0 to 8. Mean age of beaver within a colony across all states was 3 years (SE = 0.2); age ranged from 1 to 20 years; but 30% of all individuals comprised the 1-year age class. Breeding females were found in every age class except the 0- and 1-year age classes. At least one breeding female was found in 78% of all colonies and >1 breeding female was present in 17% of all colonies sampled. The youngest reproductively-active female was 2 years old; the oldest was 18 years old. Lactating and/or pregnant females were captured in every month except September, October, and November, which suggests beavers exhibit a flexible or extended breeding season in the Southeast. Knowledge of the potential composition of beaver colonies may be important when making management decisions to reduce damage.
