Effects of a late snowstorm and rain on survival and reproductive success in Columbian ground squirrels (Spermophilus columbianus)

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Abstract
Body mass changes, reproductive success, and mortality were studied in Columbian ground squirrels (Spermophilus columbianus) in southern Alberta from 1994 to 1996. Spring weather conditions varied widely between years: 1994 was a dry, warm spring, 1995 was extremely rainy, and in 1996 a major snowstorm during the first 2 weeks of May stopped foraging by ground squirrels during the latter part of their mating season. We predicted that adverse weather conditions during the mating season in general, and this snowstorm specifically, would influence reproductive success and survival. Mass changes during the first 2 weeks of May varied from year to year and reflected major differences in spring weather. Female reproductive success was highest in 1994 and lowest in 1996. In 1996, we observed a higher mass loss during the first 2 weeks of May in females that subsequently did not wean a litter than in those that did. Weaning success was higher for females that mated after the snowstorm than for those that mated before or during the snowstorm. The mortality rate during mating in 1996 was higher in males than in females and was higher than in 1994 or 1995 for both sexes. Overall weaning success of females was highest in 1994 and lowest in 1996. We concluded that the energetic costs of mating can lead to a high mortality rate for males and low reproductive success for females.