Rock squirrel (Otospermophilus variegatus) – Estes Park Trail-Gazette

The rock squirrel is a prairie dog-sized ground squirrel, approximately 10 to 12 inches in body length, with a tail of approximately 8 inches. They are light brown to mottled gray with a white eyering and ears that extend over the top of the head. They are native to North America and are found in the arid regions of the southwestern states of Colorado, Utah, Arizona, Nevada, New Mexico, Texas and even Mexico. Preferred habitat is rocky terrain, cliffs, talus slopes, and disturbed areas along roadsides with shrubby vegetation. They dig burrows that serve as refuge, birthing, and food storage chambers.

The diet of rock squirrels is mainly vegetarian and consists of leaves and shoots of plants. They also consume seeds, nuts, acorns and fruits. They will take eggs from birds and insects, and may also forage for carrion. While foraging, rock squirrels will eat some food right away, but will also collect a large number of hard mast items such as acorns for later consumption. They carry these items back to the burrow in cheek pouches, which can be very distended and in quantities of acorns and other food. Although they are primarily ground squirrels, rock squirrels climb shrubby vegetation and even taller trees to forage for leaf buds and other food, or to escape a ground predator if they are far from a burrow. They also bask on promontories such as rocks or in trees, where they can simultaneously be alert for approaching predators and warn members of the colony with their loud, piercing alarm chirp. Rock squirrels are fairly drought tolerant and can go long periods without access to water.

The social structure of rock squirrels is called polygyny, in which a dominant male mates with a group of females in a colony. The male will defend his mates and young against other males, ensuring that all young are sired by him. Females produce two litters a year, one in spring from April to June and a second in late summer from August to September. After a gestation period of one month, the 3-9 youngsters nurse in the burrow for a couple of months. Once they emerge and begin surface activity, the young are able to forage on their own. They remain close to the natal burrow during the first summer and fall, protected by their mother. During the following season, female offspring typically remain close to the home colony, while males often disperse to establish their own colony. Members of a family colony of rock squirrels maintain contact and reduce stress through tactile greetings, touching noses, and sniffing to confirm identity.

Rock squirrels may hibernate through the winter in cooler northern regions, but are active year-round in warmer southern habitats. In especially hot weather, they will enter the burrow and become inactive. This state of aestivation is similar to hibernation, but takes place to avoid hot conditions rather than subzero temperatures. Resting squirrels will adopt a slower metabolic rate and wait until temperatures moderate before becoming active again.

As with all small ground-dwelling mammals, a variety of predators will take rock squirrels when they can catch them. Hawks, snakes, and carnivores like coyotes, bobcats, foxes, and raccoons take some. As diurnal mammals, rock squirrels are primarily vulnerable to daytime predators, although snakes that hunt at night can catch them in their burrows. They have some defensive ability, sometimes rushing an attacker or throwing trash at them. Rock squirrels can also be aggressive towards other species, including humans, going after them if they feel their colony’s territory is being invaded. Their ecological role as potential food for a variety of predatory species makes rock squirrels a vital part of the arid Southwestern ecosystems where they are found. They also serve to disperse the seeds of many plant species and their burrows, when abandoned, provide shelter for other wildlife.

The IUCN lists the rock squirrel population as stable and of least concern at this time.

James Taulman is a semi-retired wildlife biologist who travels observing wildlife in New Mexico and the Southwest.