Richardson's Ground Squirrels

Sexual Differences in Behaviour of Richardson's Ground Squirrels
(also known as gophers)

The majority of differences in behaviour between male and female Richardson's ground squirrels relate to a fundamental sexual difference in how most mammals maximize their reproductive success. In general, male mammals expend energy on finding mates whereas female mammals expend energy on rearing offspring. Male and female Richardson's ground squirrels follow this typical pattern. During the mating season, male ground squirrels move longer distances, occupy larger ranges, engage in more injury-producing fights, feed less, lose more body weight, and are more likely to die than females.

The timing of the active season is based on different criteria for males and females. Female Richardson's ground squirrels time their emergence in spring such that a month later, when they give birth, they will have access to the lush green vegetation that is needed to support lactation. Males, on the other hand, time their emergence from hibernation to maximize their access to estrous females by being above ground and in breeding condition by the time the first females emerge from hibernation. During the mating season, males shift their home ranges on a daily basis in relation to daily changes in the availability of estrous females.

Both as adults and juveniles, male Richardson's ground squirrels disperse further and more often than females. Males form no lasting social bonds and they play no role in care of offspring. In contrast, females usually settle near their female kin and form life-long social bonds with close relatives such as mother, sisters, daughters, aunts, and nieces.

After the mating season has ended, adult male ground squirrels start to fatten and they are ready to immerge into hibernation in early summer. Adult female ground squirrels do not start to fatten until after they have weaned the litter, so they start hibernation several weeks later than adult males. In contrast, amongst juveniles, males enter hibernation later than females. This sex difference arises because juvenile males require more time for growth than juvenile females. The following spring, all male ground squirrels emerge from hibernation earlier than females, regardless of age.

Many males cache seeds in the hibernaculum, whereas female Richardson's ground squirrels do not store food. Males spend less time in the physiological state of torpor during hibernation than females, partly because they spend several days in the hibernaculum at the end of the hibernation season eating their food stores before they resume above-ground activity.

Related Pages:
Reproductive Behaviour
Hibernation Behavior
Population Composition
Social Organization
Annual Activity Cycle

Sources: PDFs of many of these articles can be downloaded from the Michener Publications page

  • Michener, G. R. 1998. Sexual differences in reproductive effort of Richardson's ground squirrels. Journal of Mammalogy, 79:1-19.
  • 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. 1992. Sexual differences in over-winter torpor patterns of Richardson's ground squirrels in natural hibernacula. Oecologia, 89:397-406.
  • Michener, G. R. and L. Locklear. 1990. Overwinter weight loss by Richardson's ground squirrels in relation to sexual differences in mating effort. Journal of Mammalogy, 71:489-499.
  • 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. 1984. Sexual differences in body weight patterns of Richardson's ground squirrels during the breeding season. Journal of Mammalogy, 65:59-66.
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