Spatial and temporal partitioning between eastern gray and fox squirrels in a Central Hardwood forest

Abstract Congeneric fox squirrels (Sciurus niger) and eastern gray squirrels (S. carolinensis) compete for resources within North American temperate forests. Both species exhibit regional variation in morphology and behavior—potentially due to differences in geography, community composition, or ecological pressures between forested regions. While many have studied these species in other forested regions of the United States, recent assessments of partitioning between these species in Central Hardwood forests remain scarce. We investigated spatial and temporal partitioning between squirrel species using photographic captures from camera traps at 2 scales (i.e., camera location and camera cluster) across a 16,058-km2 region of southern Illinois, United States, during January to April 2008 to 2010. We fitted single-season single-species and co-occurrence occupancy models to assess spatial partitioning at both scales and used kernel density analysis to assess temporal partitioning. We recorded 3,044 photographic captures of focal species (n = 918 fox squirrels and 2,126 eastern gray squirrels). Fox Squirrel occupancy was 0.26 ± 0.09 (SE) and 0.50 ± 0.17 at the camera location and camera cluster scales, respectively. Eastern Gray Squirrel occupancy was 0.47 ± 0.07 and 0.84 ± 0.23 at the camera location and camera cluster scales, respectively. Fox Squirrel occupancy increased with further distances to roads and had scale-dependent relationships to forest structure. Eastern Gray Squirrel occupancy increased with more hardwood basal area. Co-occurrence was influenced by distance to road at the camera location scale. We found a moderate level of activity overlap between species (Δ = 0.63, CI = 0.60 to 0.67); however, no evidence of temporal partitioning was observed. Habitat characteristics and spatial scale appear more influential in partitioning eastern gray and fox squirrels in Central Hardwood forests than peak activity.