Animal of the High Desert: Townsend's Ground Squirrel

Townsend's Ground Squirrel (Spermophilus townsendii)

Ground Squirrel

The Townsend’s Ground Squirrel is a small ground squirrel, only 6-11 inches long. They are plain gray on their backs with a lighter belly. They are often found on farms and in the desert in eastern California, southeastern Oregon, southern Idaho, western Utah, and all of Nevada. The squirrels eat mostly green plants and seeds. Townsend’s Ground Squirrels have an unusual adaptation to Idaho’s weather extremes. As soon as the grasses start turning green in the spring, the ground squirrel awakens from hibernation. Males awaken before females. They will breed soon after becoming active, and females usually have litters of 2-8 pups after a 24-day gestation period, though periods of drought may suppress breeding.

The squirrels remain active for four or five months until grasses dry out in summer. During this time period, they must store energy by gaining weight because as soon as the grasses turn brown, they begin an estivation period, or summer-time hibernation, that may continue right into winter. In Idaho, if weather conditions allow, they may awaken for a separate period of activity in the fall before entering hibernation.
During hibernation, the ground squirrel’s heart rate slows to 1-2 percent of normal and their body temperature drops to 2 degrees above the surrounding soil. When they emerge in the spring, they will have lost 25-55 percent of their body weight.

Townsend’s Ground Squirrels will form large colonies, yet they are not very social. Except when mothers have pups, there is only one Townsend's ground squirrel per burrow. They often dig two burrows—a small one in the feeding area, used as an escape hatch if predators approach, and a much bigger home burrow that is at least 50 feet long and up to 6 feet deep. Entrances to large burrows have 4-6 inch piles of dirt surrounding them. Ground squirrels dig burrows in the ground as a method of shelter and safety, and a way to get out of the heat.

The burrow network is created for communal safety. Townsend ground squirrels are an important prey animal for hawks and falcons, as well as crows, badgers, coyotes, weasels, rattlesnakes, and gopher snakes. When in danger, a ground squirrel will give alarm calls to warn closely related individuals of danger. Their calls include single-note and multi-note calls, and they also will emit faint, high pitch calls while partly or completely underground, which may serve to confuse their ground predators.

Townsend’s ground squirrels are strictly diurnal, coming above ground only during daylight hours. Their eyes are adapted to make the transition from the total darkness of the burrow to the bright light above ground. Ground squirrels have dark-yellow lenses. These yellow lenses, much like sunglasses, reduce glare from bright light and increase the contrast between colors, giving the squirrel sharper vision.

Squirrels also have exceptional focusing ability. Human eyes have a fovea centralis or a small area of the retina where cones are most densely packed and vision is most acute. Squirrels, on the other hand, have sharp vision across the entire retina, which allows a motionless squirrel to see clearly what is next to it and above it at the same time without moving its head.

Townsend’s ground squirrels are important to the desert habitat. Their digging mixes subsurface materials with surface soils, litter, and feces. This helps fertilize the soil and buries carbon, which benefits many plants and soil microorganisms. Their burrows and tunnels also allow water from high intensity storms to rapidly infiltrate into the soil instead of running off. Burrows carry oxygen deep into the soil, helping to aerate the soil around plant roots.