Long-Term Population Dynamics of The North American Beaver Castor Canadensis on Quabbin Reservation, Massachusetts, and Sagehen Creek, California

Abstract

Long-term research and monitoring activities on the Quabbin Reservation in west-central Massachusetts have provided an opportunity to follow changes in numbers and dynamics of a local unexploited beaver Castor canadensis population over a 45-year period. Beavers returned to the area in the early 1950s, following an absence of more than 200 years. Since then interpretation of aerial photographs, anecdotal reports from early researchers and watershed managers, and starting in 1968, complete annual censuses of all active beaver sites on the 5,018 ha Prescott Peninsula, have identified distinct periods of population change. The first 15 years were characterized by relatively slow growth. This period was followed by another 15 years of very rapid growth of the population. By the early 1980’s growth had slowed, and the population experienced a period of rapid decline finally stabilizing at a level approximately 23% of its peak. Various changes in productivity, colony composition, dispersal and interactions with other wildlife species were associated with these periods of population change. The changes observed in the Quabbin Reservation beaver population are comparable to changes in an unexploited beaver population in California. Research on the California beaver population has documented similar periods of rapid growth and subsequent decline.