. The Canadian field-naturalist. 148 The Canadian Field-Naturalist Vol. 86. 1 1 r 10 MAY ADULT MALES - —A ADULT FEMALES Q YOUNG J \ L D^ J \ \ L J \ \ L 20 31 10 20 30 10 20 31 10 20 31 10 20 30 iO JUNE JULY AUG. SEPT OCT Figure 2. Mean weights of adult and young ground squirrels. Sample sizes shown for each point. from Wisconsin (Jackson, 1961). At that time, adult males became inactive or hibernated and were not caught. Adult females appeared to remain active for up to a month longer, but in both sexes heavy squirrels were seldom caught after the middle of August. Mean adult weights (Fig. 2)
. The Canadian field-naturalist. 148 The Canadian Field-Naturalist Vol. 86. 1 1 r 10 MAY ADULT MALES - —A ADULT FEMALES Q YOUNG J \ L D^ J \ \ L J \ \ L 20 31 10 20 30 10 20 31 10 20 31 10 20 30 iO JUNE JULY AUG. SEPT OCT Figure 2. Mean weights of adult and young ground squirrels. Sample sizes shown for each point. from Wisconsin (Jackson, 1961). At that time, adult males became inactive or hibernated and were not caught. Adult females appeared to remain active for up to a month longer, but in both sexes heavy squirrels were seldom caught after the middle of August. Mean adult weights (Fig. 2) for both sexes declined after mid- August, and 3 of 4 individuals caught in September had lost weight from their August peaks. Young squirrels gained weight faster than adults (Fig. 2) and reached approximately the mean hibernating weight of adult females by mid-September. Young frequently remained active until late September and early October, allowing more time for weight gain. Regression of weight of young-of-the-year ground squirrels on time showed no significant differences in slope or intercept between the three years (1968, y = ±: + , N = 46, r = ; 1969, y =r ± + , N = 55, r = ; 1970, y = ± + , N r= 44, r = ). The zero intercept for 1969 is about 12 days earlier than 1970, indicating that littering may have occurred earlier that year as had adult emer- gence. By August however, the weights of all cohorts were very similar. Food Habits Stomach contents of 26 ground squirrels were examined. Seven contained animal ma- terial, primarily insects, but none contained identifiable mammal material. Vegetative ma- terial was present in all, but no identification to species was attempted. Green vegetation is available upon emergence from hibernation but species of vegetation utilized change as summer progresses (Sowls, 1948). Nine young squirrels housed in the laboratory for several months readily killed and ate labo
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