Arctic ground squirrels (Spermophilus parryii plesius) were studied in southwestern Yukon during the summers of 1977, 1978, and 1979. Samples of feces were collected from every adult captured every 2 weeks in 1978. Legumes were predominant in the diet until the fall, when squirrels switched to Artemisia. Females switched to Artemisia 1 month earlier than males, which correlates with the females' earlier entry into hibernation. Low abundance of legumes in areas in which squirrels preferred to feed indicated that squirrels fed selectively, although proximity of burrows also influenced selection of feeding sites.
Although equal numbers of males and females were weaned in a population of Richardson's ground squirrels studied in southern Alberta, interyear survival was lower for males than for females in each year of life. Consequently, the sex ratio was biased toward females in both the yearling and older adult cohorts (overall ≤ 23 males per 100 females), and maximum life-span of males was 4 years, whereas that of females was 6 years. Compared with several other species of Spermophilus, Richardson's ground squirrels have a larger litter size at birth and a shorter life-span.
Sexual Differences in Reproductive Effort of Richardson's Ground Squirrels