Reproductive Behaviour of Richardson's Ground Squirrels
(also known as gophers)
When male Richardson's ground squirrels arouse from torpor for the final time in the spring, they often remain below ground feeding on cached food for several days, during which time their weight increases and their testes enlarge and become spermatogenic. Males then emerge from hibernation and continue to gain weight until females start emerging above ground.
Once the mating season commences, males spend time monitoring all nearby squirrels, chasing off potential male competitors and assessing the reproductive condition of females. Male Richardson's ground squirrels engage in vigorous male-male competition for access to estrous females, resulting in numerous injuries to the back, hips, face, forearms, and shoulders. Increased time interacting with other ground squirrels and decreased time spent feeding results in dramatic weight loss for males.
Male Richardson's ground squirrels attempt to assess a female's reproductive status by sniffing her genital region. Non-receptive females either avoid the male's approach entirely or respond aggressively by pouncing on the male and pushing him away with the forepaws. Sexually receptive females tolerate a male's approach, and may even initiate contact with a male. Male ground squirrels persistently approach pre-estrous and estrous females, but avoid or ignore pregnant females.
On their day of estrus, most female Richardson's ground squirrels spend more time hiding and less time feeding than before or after estrus. Estrous females often adopt a hide-then-run strategy, consisting of short sprints interspersed with periods of hiding. This behaviour allows females to avoid the local male or initiate contact with a neighbouring male. If the local male sees the female leaving his area, he usually follows her. This often leads to aggressive encounters with neighbouring males. In this manner, females seem to incite competition amongst males.
Female ground squirrels are in estrus for only one day, and show a marked tendency to mate in the late afternoon. Copulation may occur above ground or in the female's burrow. At least half of female Richardson's ground squirrels mate with several males, resulting in multiple paternity of the litter.
Once pregnant, 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.
Sources: PDFs of many of these articles can be downloaded from the Michener Publications page
- Michener, G. R., and I. G. McLean. 1996. Reproductive behaviour and operational sex ratio in Richardson's ground squirrels. Animal Behaviour, 52:743-758.
- Michener, G. R., and L. Locklear. 1990. Differential costs of reproduction for male and female Richardson's ground squirrels. Ecology, 71:855-868.
- Michener, G. R. 1989. Reproductive effort during gestation and lactation by Richardson's ground squirrels. Oecologia, 78:77-86.
- Michener, G. R. 1985. Chronology of reproductive events for female Richardson's ground squirrels. Journal of Mammalogy, 66:280-288.
- Michener, G. R. 1983. Spring emergence schedules and vernal behavior of Richardson's ground squirrels: why do males emerge from hibernation before females? Behavioral Ecology Sociobiology, 14:29-38.
- Michener, G. R. 1980. Estrous and gestation periods in Richardson's ground squirrels. Journal of Mammalogy, 61:531-534.
By other authors:
- Hare, J. F., G. Todd, and W. A. Untereiner. 2004. Multiple mating results in multiple paternity in Richardson's ground squirrels, Spermophilus richardsonii. Canadian Field-Naturalist, 118:90-94.