Reproductive behaviour and operational sex ratio in Richardson's ground squirrels

Abstract

Activity budgets, use of space and social interactions of adult Richardson's ground squirrels, Spermophilus richardsonii, during the annual mating season were documented in relation to daily operational sex ratio (OSR) for males and in relation to reproductive status for females. For males, mating was a stressful period characterized by weight loss and injury. Male–male conflict was highest when receptive females were most abundant and OSR was least male-biased. Neighbouring males seemed to jockey for position on a daily basis to increase their proximity to those females in oestrus that day. Males spent more time monitoring conspecifics and less time feeding during the mating period than at other times, especially in the late afternoon of the few days on which most females copulated, often with several males. Between emergence from hibernation and emergence of the litter 8 weeks later, the activity budget of females changed little except for the day of oestrus, when females fed less and spent time hiding. Some oestrous females spent more than 20% of their time above-ground hiding, and some precipitated aggression between males by using a hide-then-run behavioural pattern to move outside their usual area of residence. Females in oestrus temporarily expanded their home range, and they had some ability to determine the identity and sequence of their mating partners.