Consequences of a Temporally and Spatially Variable Food Supply for an Unexploited Gray Squirrel (Sciurus carolinensis) Population

Abstract

-The demography and spatial distribution of a gray squirrel (Sciurus carolinensis) population was studied with respect to differences in habitat quality and food production in a heterogeneous Delaware woodlot from 1972-1973. In 1971 a large mast crop was produced, followed by a poor 1972 crop and a partial recovery in 1973. The squirrel population declined from 116 individuals in summer 1972 to 82 in fall 1973. Major components of the decline were losses of 1972 juveniles and 2-5-year-old females, and curtailed breeding in 1973. Squirrels were segregated among five study plots that represented areas of differing habitat quality and food production within the woodlot. The distribution of the sexes among the plots was significantly heterogeneous in summer and fall 1972 and summer 1973 (P < 0.10, G-test); plots with poorer mast production had a preponderance of females (R percent of individuals = 62%) while males predominated in plots with the best mast resources (R = 64%). In particular, adult males and yearlings (both sexes) were skewed towards high-mast plots while adult females were more abundant in low-mast plots. Juveniles showed no discernable pattern of distribution among plots. Losses were greater than expected from low-mast plots and less than expected from high-mast plots, especially for juveniles, yearlings, and females. The pattern of spatial variation of food abundance, sex (and possibly age) ratios and disappearance rates suggests a model of population regulation in which subordinates are relegated to suboptimal sites and bear major stress and losses when population density is high and food resources dwindle.