California Ground Squirrel

California Ground Squirrel, Spermophilus beecheyi

California Ground Squirrel, Spermophilus beecheyi. Photographs taken in the greater San Diego area, May 2018.

The California Ground Squirrel, Spermophilus beecheyi, is a member of the Sciuridae Family of Squirrels, Chipmunks, Marmots and Prairie Dogs. The Sciuridae Family consists of two hundred seventy-nine species placed in fifty-one genera and five subfamilies. There are thirty-eight species in the Spermophilus genus. The California Ground Squirrel is also known as the Beechey Ground Squirrel and in Mexico as Ardilla de Tierra de California.

California Ground Squirrels have gray, white, light brown, and dark brown mottled fur. Their shoulders, neck, and sides are a lighter gray while their underside is a lighter combination of light brown, gray, and white. Their bushy tail is a mix of the colors that appear on their back. They have a white ring around each eye and black fur on the outer rim of their ears. They range from 33 cm (13 inches) to 51 cm (20 inches) in length and weigh between 280 g (10 oz) and 738 g (1 pound 10 oz). Their tail is typically 13 cm (5 inches) to 23 cm (9 inches) in length.

California Ground Squirrels have a polygynandrous mating system, meaning that both males and females in this species have multiple mates during the breeding season. Mating occurs in early spring, typically for only a few weeks. As with most ground-dwelling squirrels, breeding occurs just after the animals emerge from their winter burrows. The exact time of mating is highly dependent on the climate and area the squirrel inhabits, since the timing of hibernation varies with ecological factors such as elevation and geography. In general, populations at higher altitudes and in colder climates hibernate for longer periods and thus breed later than those found at lower elevations and in warmer climates. Male California Ground Squirrels possess abdominal testes which drop into a temporary scrotum during the breeding season only. Females produce one litter per year after a gestation period of approximately one month. Litters range in size from five to  eleven young and the sex ratio is typically 1:1. Young squirrels, called pups, are born altricial and do not open their eyes until they are about five weeks old. Females give birth to their pups in a burrow, and will move their young into new burrows frequently to avoid predation. Parental care is only provided by the mother. Pups first leave their burrows at five to eight weeks of age, shortly after opening their eyes, and are weaned between six to eight weeks of age. Pups may begin to burrow at eight weeks of age and reach sexual maturity not sooner than one year old. In their first year of life, some ground squirrels remain above ground and do not hibernate. California Ground Squirrels have live spans of six years in the wild and ten years in captivity.

California Ground Squirrels live in burrow systems that can house many generations. Each individual has an entrance of their own and they tend to stay within 150 yards (450 feet) of their burrow system, usually retreating only to their entrance of that burrow system. They frequently spend time sunning themselves and depending upon the climate, they may hibernate or aestivate to escape undesirable temperatures. Males are more aggressive than females and sometimes appear territorial. California Ground Squirrels have a primarily seed-based diet and use their cheek pouches while they are foraging to collect more food than would otherwise be possible in one sitting. In addition, they are also known to cache food. They consume seeds, barley, oats, acorns, gooseberries, pears, Quail eggs, roots, bulbs, and fungi. They include insects in their diets when they are available, and have been known to consume grasshoppers, Crickets, Beetles, and Caterpillars. In turn, the California Ground Squirrel is highly vulnerable to predation due to their diurnal habits, open habitat, and concentration of conspecifics found in any particular colony. They are preyed upon by Badgers, Bobcats, Coyotes, Dogs, Eagles, Foxes, Hawks, House Cats, Pumas, and large Snakes. 

The California Ground Squirrel is easily confused with the Fox Squirrel, Sciurus niger, due to their similar appearances and overlapping ranges. The Fox Squirrel can be distinguished by its rusty-colored belly, longer tail with a black outline,  and larger stature.

California Ground Squirrels are found in portions of southern Washington, most of Western Oregon, most of California,  western Nevada, and the northwestern part of the Baja Peninsula. They are terrestrial and semifossorial, requiring habitats with some loose soil where they can excavate burrows. They have successfully exploited many habitat types including, coastal areas, fields, pastures, grasslands, and oak woodlands. Although, they do not inhabit deserts. They can be found down in valleys and on mountains at elevations up to 2,200 m (7,200 feet). They also occupy urban, suburban, and agricultural areas.

From a conservation perspective, the California Ground Squirrel is listed as Least Concern due to their wide distribution, presumed large population size, and tolerance of a broad range of habitats. No major threats have been identified for this species.