Richardson's Ground Squirrels

Annual Activity Cycle of Richardson's Ground Squirrels
(also known as gophers)

Although Richardson's ground squirrels can be seen above ground from mid-February to late October, no individual animal is active throughout this period. Adult males and adult females are active for about 4 months of the year and hibernate for the remaining 8 months. Juveniles are born underground and first appear above ground when about 1 month old, by which time their parents have been out of hibernation for about 2 months. Juveniles then remain active for about 3.5 months if female or 5-6 months if male.

ground squirrel active seasons
Timing of the active season differs for each age and sex class of Richardson's ground squirrels. All age and sex classes are simultaneously active for only a few weeks in May and June in southern Alberta.

Dates of annual events may vary by several weeks between years, and events usually occur several weeks later in more northerly and easterly locations of the geographic range compared with southern Alberta.

Hibernating adult male Richardson's ground squirrels terminate their final torpor bout in mid-February in southern Alberta. They usually spend several days underground in the hibernaculum in a state of euthermy, eating cached seeds, before they resume above-ground activity in mid- to late February. Access to cached food in the hibernaculum allows males to gain weight and initiate testicular recrudescence in preparation for the mating season even before they first emerge above ground. Adult female Richardson's ground squirrels emerge from hibernation in March, about two weeks after the males. Unlike males, females do not store food in the hibernaculum and they emerge above ground almost immediately after termination of their final torpor bout.

emergence data graph
Cumulative percent of adult (≥1 year) male and female Richardson's ground squirrels emerged from hibernation.
Source: Michener (1983).

Within a few days of emergence from hibernation, females enter a short estrous period. Female Richardson's ground squirrels mate with 1 to 4 males. Once pregnant, females become intolerant of all males.

Parturition occurs underground after 23 days of gestation, in late March to early April in southern Alberta. Females have only one litter a year, with an average of 6-7 young. Infants remain underground for 29-30 days, entirely dependent on mother's milk for nutrition. Litters emerge from the natal burrow system in late April to early May, and juveniles immediately begin to eat solid food. As soon as the litter is weaned, the mother begins fattening in preparation for hibernation.

All age and sex classes are simultaneously active above ground for only about 5-6 weeks, just the period from when litters emerge until adult males resume hibernation. Adult male Richardson's ground squirrels immerge into hibernation in June in southern Alberta. Adult females start to hibernate about 2 weeks later than adult males, immerging in late June to early July.

Juvenile females immerge into hibernation in August, by which time they have attained 80% of adult size. Juvenile males remain active until mid-September to October, by which time they have attained full adult size.

From November through mid-February, all Richardson's ground squirrels are in hibernation. Then the annual cycle repeats, with yearling and older males emerging from hibernation synchronously, despite the several-month difference in when they entered hibernation the previous year. Yearling and older females also emerge synchronously, about 2 weeks after the males.

Related pages:
Hibernation Physiology
Annual Weight Cycle

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

  • Michener, G. R. 2002. Seasonal use of subterranean sleep and hibernation sites by adult female Richardson's ground squirrels. Journal of Mammalogy, 83: 999-1012.
  • 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 J. W. Koeppl. 1985. Spermophilus richardsonii. Mammalian Species, 243:1-8.
  • 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 and Sociobiology, 14:29-38.
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