Seasonal and year-to-year differences in food selection by beavers.

Selection of trees for food by a colony of beavers in central Massachusetts was studied from September 1972 through April 1974. The beavers exhibited both seasonal and year-to-year differences in preference for certain genera. Pine was selected against during fall but not spring, and there was a switch in preference from birch during fall 1972 to oak and witch hazel in fall 1973. These differences may partly reflect greater seasonal stability in concentrations of stored nutrients in coniferous tree bark than in deciduous tree bark, and greater year-to-year stability in bark concentrations of stored nutrients in non-mast-seeding species than in mast-seeding species (1972 was a mast year for oaks in central Massachusetts).