Annual Variation of Spring Emergence and Breeding in Columbian Ground Squirrels (Spermophilus columbianus)

Abstract

Times of breeding were documented over 6 and 7 years for two populations of Columbian ground squirrels at different elevations in southwestern Alberta, Canada. The pattern of spring emergence from hibernation at the low elevation was typical for ground squirrels; adult males emerged first, adult females slightly later, and yearlings of both sexes last. Time of conception was highly correlated with time of emergence. Breeding was always later and year-to-year variation was greater in the population at the high elevation, where snow depth in spring, an index of the time of melt-off, was correlated with breeding dates. At this site reproductive success, but not survival, was greater in years when breeding was early. At the lower site, cold temperatures in spring appeared to delay emergence and breeding, and most females emerged during periods of relatively high temperature; neither survival nor reproductive success varied consistently with time of breeding. Overall, survival was greater and reproductive success was lower in the population at the higher elevation.