Survival and reproductive effort of female Columbian ground squirrels (Spermophilus columbianus) were examined for 1 year following experimental manipulation of litter size that either increased, decreased, or left their lactational cost of reproduction unmanipulated. Except for a trend towards females that incurred decreased costs in year 1 being heavier than other females at spring emergence in year 2, no short-term cost of reproduction was detected. The results fail to support the assumption of reproductive costs implicit in most life-history models, and are in accord with an earlier correlational study of reproduction of Columbian ground squirrels that found no trade off between current and future reproductive success.