Variability in Reproductive Output and Success of Spermophilus elegans Ground Squirrels

Abstract

Reproductive output and success of female Spermophilus elegans inhabiting a montane pasture in the Colorado Rockies were examined from 1977 to 1979. Females that successfully raised young to postweaning age occupied specific burrow sites each year. These sites were termed maternity-burrow sites and, based on frequency of annual reoccupancy, were classified as frequently-occupied (type 1) or occasionally-occupied (type 2) sites. Mean litter sizes at weaning for females that occupied type 1 sites were significantly greater in each year and overall than for females from type 2 sites. Of all young weaned, approximately an equal proportion survived to become yearlings from each site type. Significantly more surviving young from type 1 sites reproduced, however. Thus, females at type 1 sites were more fit than those at type 2 sites. Variability in reproductive output and success of Spermophilus elegans females was attributed to age of female in conjunction with type of maternity burrow site occupied.