Habitat Specialization and Social Factors in Distribution of Red and Gray Squirrels

Abstract

The spatial distribution, habitat specialization, use of food supply, and interspecific behavior within coexisting populations of red squirrels ( Tamiasciurus hudsonicus ) and gray squirrels ( Sciurus carolinensis ) and the social organization of red squirrels were examined in a 10.2-ha mixed forest in northern Wisconsin during June 1974–March 1976. Habitat specialization, not interspecific aggression, determined differences in distribution of red and gray squirrels. Distribution and abundance of each species were related to production of principal seed foods. Population densities of red squirrels were highest in fir ( Abies )-cedsir ( Thuja ) cover and in pine ( Pinus ) cover in months following high production of cones. Sighting densities of gray squirrels were highest in mature cover of maple ( Acer )-oak ( Quereus ) throughout the year and were correlated with tree size of red oak ( Quercus rubra ). Both species consumed seeds of maple, oak, and hazel ( Corylus ); red squirrels also fed on conifer seeds. Interspecific aggression between red and gray squirrels was rare. Adult red squirrels usually established territories defended solely against conspecifics. Territories were less stable than those found in western conifer forests.