Litter Size in Columbian Ground Squirrels (Spermophilus columbianus)

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Abstract
Measures of litter size, based on counts of corpora lutea, placental scars, embryos, and juveniles emerging from natal burrows, were determined from 181 Columbian ground squirrels (Spermophilus columbianus) collected in three areas in southwestern Alberta, Canada, and from observations of 88 litters that emerged in these areas. Most measures of litter size differed between areas and were lower at a high elevation site (2,170 m) than at the other two sites (elevation 1,500 m). We suggest that differences between areas may be related to timing of snow melt and onset of vegetative growth. Columbian ground squirrels have smaller litters than most other North American species of ground squirrel, perhaps reflecting different life history tactics.