Sympatric Behavior of Tree Squirrels in an Urban Environment

The eastern gray squirrel (Sciurus carolinensis) and fox squirrel (Sciurus niger) are ubiquitous in urban ecosystems like university campuses despite the habitat loss and fragmentation often associated with urbanization. While populations of both species usually do not overlap in their native geographic ranges, gray and fox squirrels are sometimes forced into coexistence in urban habitats where fewer green spaces are available. The coexistence of both species at Butler University in Indianapolis, Indiana refutes the competitive exclusion principle, and niche partitioning is likely necessary for them to coexist. This study assessed the activity patterns of fox and gray squirrels at Butler to determine if the two species partition the campus spatially or temporally to avoid interspecific competition. Different areas of a survey transect established throughout campus were characterized spatially into “high” or “low” canopy areas based on percentages of tree canopy cover, and observations of both species were made during three different time periods throughout the day. An analysis of observations between species in different canopy groups and at different times of day found evidence for spatial partitioning. In the summer, gray squirrels were more frequently active in high canopy areas, while fox squirrels were more frequently active in low canopy areas. There was little evidence for temporal partitioning throughout the day, as the activity of both species did not typically vary between time periods. Behavior of fox and gray squirrels did change between seasons. In the fall and winter, fox squirrels were equally active in high canopy areas as they were in low canopy areas, and they outnumbered gray squirrels in both types of habitat. Gray squirrels remained more active in high canopy areas as they were in low canopy areas. The difference in variation between seasons indicates temporal partitioning may occur seasonally.