Urocitellus richardsonii (Sabine, 1822)
Richardson's Ground Squirrel
Basis for Listing
Richardson’s Ground Squirrel (Urocitellus richardsonii) is found in grassland habitats of Minnesota’s western counties (Prairie Parkland). Its range extends across the northern Great Plains, from Minnesota west to Montana. Minnesota is at the eastern boundary of the species’ range in the United States, and populations are declining due to a lack of suitable habitat and persecution by humans. Historically, the Richardson’s Ground Squirrel thrived in native prairie habitatas, but most of this landscape has been converted to agriculture (Minnesota's Remaining Native Prairie). Richardson's Ground Squirrel was listed in Minnesota as a species of special concern in 2013.
Richardson’s Ground Squirrels are 30 cm (11.8 in.) from snout to tip of tail and weigh 249.3-396.7 g (8.8-14 oz.) (Hazard 1982). They are the heaviest of Minnesota’s ground squirrels and have uniformly gray fur, with yellow on the face, shoulders, and sides. The species it is most often confused with is the Franklin’s Ground Squirrel (Poliocitellus franklinii). Richardson’s has a wider skull and a shorter tail, while the Franklin’s Ground Squirrel has a long head and a bushier tail (Hazard 1982).
Richardson’s Ground Squirrels are found in open habitat, preferring dry well-drained soils for burrowing. Short vegetation and high visibility is important for detecting potential predators. A species of the tallgrass and short grass upland prairies, Richardson’s Ground Squirrels can also be found in grazed pastures and open urban areas in western Minnesota.
Biology / Life History
Richardson’s Ground Squirrels have an interesting approach to hibernation that reduces competition between the sexes and age classes. Each sex or age group spends only four months of the year above ground, and much of that time is spent eating in order to create enough fat deposits to last through hibernation. Males are the first to awake from hibernation in late March; they mate, fatten up, and reenter hibernation in early July. Females emerge from hibernation in early April and usually mate after their third day out of hibernation (Michener 1999). Gestation lasts 22-23 days, and they give birth to litters of approximately six young. Juveniles quickly switch from nursing to eating leaves and seeds. Only a few weeks after the young have left the nest (late July), the adult females reenter hibernation (Hazard 1982). From August to mid-October, the first-year juveniles are the only Richardson’s Ground Squirrels that are not hibernating. Juvenile males remain above ground the longest in the fall and eat until they reach adult size before hibernating. Richardson's Ground Squirrels eat mostly green vegetation and forage above ground during the day. This species grows fatter and reaches larger skeletal size when living near cropland, rather than in native prairie vegetation (Hazard 1982).
The mating season is an intense time for Richardson’s Ground Squirrels, with many fights and long chases between males (Michener 1999). Between the serious wounds from fighting and their fat reserves becoming diminished, many males do not survive the mating season. In order to prepare for the demands of mating season, males store food in their hibernacula to replenish their fat reserves before they emerge in the spring. During mating season, females are only receptive to males for three hours. They will usually mate with multiple males but become aggressive towards all males once they are impregnated. They choose their nesting chamber and have their litter in isolation. Lactating females choose territories located in low spots on prairies that have access to abundant vegetation for food (Hazard 1982).
Richardson’s Ground Squirrels have two alarm calls, one for aerial predators and another for terrestrial predators. They give chirps of descending sound frequency when a hawk is spotted and a long high-pitched whistle when a weasel or coyote is spotted (Michener 1999). Responses differ depending on which type of call is given. The ground squirrels will run for cover if an aerial alarm call is given and stand up on their hind legs and look around if a terrestrial predator alarm is sounded.
Conservation / Management
The Richardson’s Ground Squirrel was historically found on tallgrass prairie; however, the landscape of western Minnesota has been largely altered from prairie to farmland. Richardson's Ground Squirrels have adapted and are able to live in open areas such as cow pastures and old fields. However, they are considered agricultural pests due to their burrowing habits and taste for grain and other agricultural products.
Conservation Efforts in Minnesota
More surveys are needed to locate new populations, and existing populations should be monitored to determine the current status of this species in Minnesota.