Spermophilus tereticaudus
round-tailed ground squirrel

Round tailed ground squirrels, Spermophilus tereticaudus, live in desert areas of the southwest United States and Mexico, including Arizona, California and northern Mexico. They are present in portions of the Mojave, Yuma, and Colorado deserts (Cockrum, 1982). (Cockrum, 1982)

Spermophilus tereticaudus "inhabits sandy arid regions of the Lower Sonoran Life Zone (Ernest and Mares, 1987)." It often occupies dunes and shrubs in lower flatter areas. Its burrows have been found among shrubs, and in sand of dunes, especially in areas with dense sand. Its habitats are normally characterized by extreme temperatures with low humidity (eg. -5 C to 39 C during one week)(Ernest and Mares, 1987). (Ernest and Mares, February 27 1987)

Spermopilus tereticaudus is a small ground squirrel. It has a long round tail; and long, broad, and hairy hind feet (Ernest and Mares, 1987). Their fur is uniform and without markings or stripes. The underside or their body is paler, and it appears uniform from tip to tail (Hall, 1981). The summer fur color is paler and brighter than the winter pattern. Spermophilus tereticaudus molts two times per year, once in the spring and once in fall.

The skull is rounded with a short rostrum, and a post orbital process is present. Body mass fluctuates according to season, however, the average mass is 125 g (Ernest and Mares, 1987).

Spermophilus tereticaudus does not hibernate. Instead, they go into torpor during the winter months. They emerge in January and February, during the precopulatory phase, and after the juvenile disperal in June and July they resume their inactive phase (Aug. or Sept until January). Short periods of activity have been noted during the inactive season, (Ernest and Mares, 1987). In laboratory settings, food deprivation can trigger torpor (Ernest and Mares, 1987).

While active, these squirrels show two peaks in their activity, one in the morning, and one in the late afternoon. This pattern may lower the amount of time S. tereticaudus is exposed to the heat. These squirrels have been shown to have long periods of activity on overcast afternoons. When active, they spend about 50% of their time foraging (Ernest and Mares, 1987).

Spermophilus tereticaudus communicates using whistles. Their warning is a single whistle. When emitted, it causes the other animals in the area to run to their burrows and then look around. Females sound warning whistles more often than males. Since the females have been found to be more closely related to the their neighbors than the males, it is suspected that this behavior enhances inclusive fitness (Dunford, 1977).

Spermophilus tereticaudus have a semicolonial social organization, but their burrows are individual, and other individuals are chased away if they get too close. It is interesting to note that males are dominant from January until March (during breeding season) and females are dominant from March to April (during raising of young)(Dunford, 1977). (Dunford, 1977; Ernest and Mares, February 27 1987)

Spermophilus tereticaudus communicates using whistles. Their warning is a single whistle. When emitted, it caused the other animals in the area to run to their burrows and then look around (Dunford 1977). (Dunford, 1977)

Spermophilus tereticaudus is an omnivore like many other sciurids. Their diet includes a large proportion of green vegetation, but also seeds, and to a lesser extent, insects. During the spring, 80% of their diet consists of green vegetation, while 15% is represented by seeds, and 5% is represented by insects. In the summer, all of their diet is composed of green vegetation. In winter, however, their reliance on vegetation drops, and they again use seeds. When they do eat insects, they consume mainly ants, termites and grasshoppers (Ernest and Mares, 1987). They focus their diet on foods that have a high water concentration. This is necessary because they live in desert conditions, and cannot survive on dry foods. The average water content of the food they eat is 80% (Ernest and Mares, 1987). (Ernest and Mares, February 27 1987)

Although not specifically reported upon, it is likely that these squirrels are prey for other animals. Because of their diurnal and semi-fossorial habits, likely predators include canids, felids, snakes, and hawks. This species uses alarm signals, and these may help the squirrels evade predators.

The role of these ground squirrels in their ecosystems has not been documented. Because they are omnivorous, it is likely that they have some impact on plant and insect populations. As a possible prey species, S. tereticaudus is likely to have some influence on predator populations as well. Because they dig burrows, these animals contribute to soil aeration.

They tend to live near cultivated fields, and may eat the alfalfa and dates grown. Thus, they come into conflict with humans, but it is not much of a problem (Ernest and Mares, 1987) (Ernest and Mares, February 27 1987)

These animals are not documented to have any positive economic effect on humans.

Spermophilus tereticaudus seems to be doing relatively well. Its habitat is not being destroyed significantly, and it seems to have a relatively good hold in its native areas (Ernest and Mares, 1987). (Ernest and Mares, February 27 1987)