Richardson's Ground Squirrels

Habitat & Home Range of Richardson's Ground Squirrels
(also known as gophers)

Richardson's ground squirrel

Richardson's ground squirrels inhabit the short and mixed-grass prairies of North America, including portions of Alberta, Saskatchewan, and Manitoba in Canada and parts of Montana, North Dakota, South Dakota and Minnesota in the United States. Richardson's ground squirrels prefer open terrain with high visibility, allowing them to detect approaching predators. Although about 80% of natural prairie habitat has been converted to agricultural and urban areas, Richardson's ground squirrels fare well in human-modified habitats such as city parks, over-grazed pastures, edges of cultivated fields, and perennial crop fields.

As adults, each Richardson's ground squirrel occupies a home range including one or several burrow systems, and allows only its closest kin to intrude. The core area of the home range includes the main burrow system as well as favourite feeding sites, and covers 20-40 m2 during the active summer season. The size of each squirrel's territory varies, depending on season, sex, and age of the squirrel.

Adult female Richardson's ground squirrels

At the time she is ready to mate, a female's range is overlapped by the ranges of several males, but overlap between males and females decreases post-mating. The size of a female's home range increases from early spring to summer, with maximum size occurring shortly after juveniles have become independent. Home range during the summer months averages about 240 m2, and the range often overlaps the ranges of neighbours, especially if those neighbours are close kin such as sisters or adult daughters. With increasing home-range size, extent of overlap with neighbouring females increases, although the core areas where females concentrate 50% of their time usually do not overlap. Range size decreases as hibernation approaches.

Adult male Richardson's ground squirrels

During the mating season, male squirrels do not defend a well-defined territory. Instead, on a daily basis, males adjust the location of their range to increase their proximity to the females that are in estrus on that day. On average, a male Richardson's ground squirrel's range overlaps the ranges of at least one neighbouring male and 10 estrous females during the mating season.

After the mating season, the home ranges of males decrease in part due to the behaviour of pregnant and lactating females, who exclude males. As hibernation approaches, the ranges of males decrease further.

Juvenile Richardson's ground squirrels

litter of Richardson's ground squirrels

When they first emerge from the natal burrow at about 29-30 days of age, juveniles initially stay close to home. Throughout the summer, juvenile Richardson's ground squirrels maintain a core area that overlaps extensively with those of their mother and siblings, but rarely overlaps with core areas of unrelated squirrels. As the active season progresses, juveniles acquire their own distinct areas and overlap declines.

Juvenile female Richardson's ground squirrels tend to be sedentary, appropriating a section of their mother's home for their own use. In areas of high population density, juvenile females may move a short distance away from the natal area as a result of limitations to the number of offspring that can share a mother's home range.

Long-distance dispersal from the natal territory is usually male biased. Juvenile male Richardson's ground squirrels typically disperse in June and July, when they are 2-3 months old, or disperse as yearlings after hibernation. Because of the difficulty of tracking males once they start to disperse, very little information is known about how far they travel or how many of them are successful at establishing themselves in another population. One ear-tagged male was found 6 km from where he was born. Males may stay in the natal area if population density is low and the number of siblings is small, but males that remain near their birth area do not subsequently mate with nearby close kin (sisters or mothers).

The spatial patterns established as juveniles are maintained into adulthood; hence, most female squirrels spend their lives surrounded by female kin, whereas most males do not live near kin of either sex. Sex-biased dispersal, characterized by males being more likely to leave the natal area and moving father than females when they do, is typical of all species of ground squirrels. One consequence of sex-biased dispersal is separation of close kin of opposite sexes, which reduces the likelihood of inbreeding.

Related Pages:
Reproductive behavior
Social organization

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.
  • van Staaden, M. J., R. K. Chesser, and G. R. Michener. 1994. Genetic correlations and matrilineal structure in a population of Spermophilus richardsonii. Journal of Mammalogy, 75: 573-582.
  • 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.
  • Michener, G. R. 1981. Ontogeny of spatial relationships and social behaviour in juvenile Richardson's ground squirrels. Canadian Journal of Zoology, 59: 1666-1676.
  • Michener, G. R. 1979. Spatial relationships and social organization of adult Richardson's ground squirrels. Canadian Journal of Zoology, 57: 125-139.
  • Michener, G. R. and D. R. Michener. 1977. Population structure and dispersal in Richardson's ground squirrels. Ecology, 58: 359-368.
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