Notes on age at dispersal of beaver (Castor fiber) in an expanding population

Movements of nine young beavers (Castor fiber) that were trapped at the front of an expanding population were monitored using radiotelemetry. Two years is generally considered the normal age at dispersal in beavers, but in this study the ages at dispersal were evenly distributed between 11 and 23 months. At least one of the females in the study gave birth at 2 years of age. Exploratory movements of three individuals outside the natal terrritory before the time of dispersal were observed. The observed plasticity in age at dispersal and parturition indicates that the rate of increase may be greater than expected at the front of expanding beaver populations.