Scientific Name: Genus Spermophilus and allied genera
Colorado is home to several different species of ground squirrel: the thirteen-lined and the spotted ground squirrels; the grizzled brown rock squirrel, with its distinctive long tail; the brownish gray, obscurely dappled Wyoming ground squirrel; the white-tailed antelope squirrel and the golden-mantled ground squirrel. Nearly every part of Colorado is home to at least one species of ground squirrel. All ground squirrels are active in the day; most are common and readily identified and observed. Ground squirrels range in size from tiny spotted ground squirrels, barely larger than a chipmunk, to rock squirrels 20 inches long, as large as some tree squirrels.
On the grasslands of the eastern plains (and also in the southwest) are the thirteen-lined and spotted ground squirrels. Along the foothills and on western mesas and canyons lives the rock squirrel. The Wyoming ground squirrel lives in mountain parks and the 13-lined ground squirrel is a common ground squirrel in Colorado. The white-tailed antelope squirrel lives in the hot desert shrub-lands of western valleys. And the golden-mantled ground squirrel lives throughout the mountains.
Ground squirrels feed mostly on seeds and fruits, although most will eat flowers, buds and some leaves and insects as available. In fact, the thirteen-lined ground squirrel thrives on grasshoppers in season, making it a valuable citizen on grazing lands. Most ground squirrels store fat for the winter and are deep hibernators. The rock squirrel is an exception, arousing to feed periodically on stored seeds and acorns through the winter.
Most ground squirrels mate in spring and have a single litter of a half dozen or more young a year after a gestation period of about a month. The rock squirrel is, again, the exception to the rule, females often have two litters.
By David M. Armstrong Department of Ecology & Evolutionary Biology Environmental Studies Program, University Museum of Natural History University of Colorado-Boulder