Chronology of Reproductive Events for Female Richardson's Ground Squirrels

Abstract

Timing of reproductive events for adult (≥ 1-year old) female Spermophilus rich-ardsonii in southern Alberta was determined from 1979 to 1984 by daily monitoring of squirrels following emergence from hibernation until litters emerged from the natal burrow. Females typically mated 3 to 5 days after emergence from hibernation and gave birth 22 to 23 days later. Juveniles were usually 28 to 30 days old when they first left the natal burrow. Thus most litters (130/175) appeared 53 to 58 days after the mother had emerged from hibernation. The reproductive chronologies of yearling and older females were virtually identical. The 22.5-day gestation period of S. richardsonii is the shortest documented for the genus. Interspecific comparison of reproductive chronologies of ground squirrels indicated that at least five species in the subgenus Spermophilus typically wean litters ca. 8 weeks after the mother's emergence from hibernation, whereas for several species in other subgenera the mother emergence-to-litter emergence interval exceeds 10 weeks.