The costs of reproduction in female columbian ground squirrels

The cost of reproduction for female Columbian ground squirrels was assessed using seven years of data from three populations in southwestern Alberta, Canada. Short-term costs, measured as reduced survival or lowered subsequent fecundity, were not directly associated with whether a female reproduced or not, nor with the females' litter size. In one of the populations, females that first reproduced as yearlings had slightly shorter lifespans, but almost 1.5 times the lifetime reproductive success, compared to those that first reproduced when older. Although short-term reproductive costs were not apparent from our data, we cannot conclude that reproduction was not costly. Such costs might exist but be masked by females' adjusting reproductive investment to their body condition. A weak association of spring (minimum) body weight of females and subsequent reproduction supported this possibility, as did correlated increases in body weight and litter size in a population given supplemental food.