When male Richardson's ground squirrels arouse from torpor for the final time in the spring, they remain below ground feeding on cached food (see Hibernation) and will often begin testicular regrowth. (see Reproductive Physiology) They then emerge from hibernation and acquire territories before the emergence of females.
As the breeding season commences, males spend more time monitoring all nearby squirrels, chasing off potential competitors and assessing the reproductive condition of females than they do at other times of the year. They also spend less time feeding, resulting in a dramatic weight loss. (see Annual Weight Cycle)
Males undergo vigorous intrasexual competition for access to estrous females, resulting in numerous injuries to the back, hips, face, forearms and shoulders. In contrast, females are rarely injured. Male ground squirrels also shift the location of their core areas on a daily basis in an attempt to remain near estrous females. While females tend to be sedentary, male ground squirrels show little fidelity to particular burrows during the breeding season.
Male Richardson's ground squirrels identify females by sniffing her nose and body, and then attempt to assess her reproductive status by sniffing the genital region. Females may either avoid the male's approach entirely or will respond aggressively by pouncing on the male and pushing him away with the forepaws. Sexually receptive female ground squirrels will tolerate a male's approach, and may even initiate approaches. Male ground squirrels will persistently approach pre-estrous and estrous females, but avoid or ignore pregnant females.
On their day of estrus, female Richardson's ground squirrels undergo a change in behaviour. Females spend more time hiding and less time feeding than before or after estrus. This results in a brief interruption in weight gain. (see Annual Weight Cycle) They may also adopt a hide-then-run strategy of short sprints followed by periods of hiding. This behaviour brings them outside their normal range, and may be used to avoid the local male or initiate contact with a neighboring male. If the local male sees the female leaving her territory, he usually follows. This often leads to aggressive encounters with other males. In this manner females seem to incite competition.
Female ground squirrels are in estrus for only one day, and show a marked tendency to mate in late afternoon. Copulation may occur above ground or in the female's burrow. At least half of female ground squirrels mate with several males, resulting in multiple paternity of the litters. A female can only produce one litter a year.
After estrus, females devote more
time to grass gathering and excavation. They do not tolerate the
presence of any males, not even their mate(s). Males play no part
in rearing offspring.