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ROCK SQUIRREL<br />
Spermophilus vat iegatus<br />
Distribution.--The rock squirrel is found from southern Mexico to<br />
northern Utah and Colorado and is locally abundant in rocky habitats.<br />
In Colorado it is found in Front Range canyons and quarries north to the<br />
Cache la Poudre drainage. In the course <strong>of</strong> this study the rock squirrel<br />
was observed in a wall at the south end <strong>of</strong> the Mesa Trail.<br />
Description. --The rock squirrel is distinguished from other ground<br />
squirrels by its large size and long tail. The tail is not as bushy as<br />
the tail <strong>of</strong> a tree squirrel. The color is grayish black mixed with<br />
cinnamon brown, sometimes with the head and face blackish. There is a<br />
slightly mottled effect over the whole body.<br />
Mean (and extreme) external measurements <strong>of</strong> five females from southern<br />
Colorado were: total length, 470 (440-498); length <strong>of</strong> tail, 197.2 (176-<br />
223); hindfoot, 59.2 (58-60); ear, 30 (29-31). Mean weight <strong>of</strong> females<br />
in Utah was 550 grams in the spring and 750 grams in the autumn. Greatest<br />
length <strong>of</strong> skull varies from 57.6 to 63.5 (mean, 60.56); zyg-omatic breadth<br />
varies from 35.6 to 39.1 (mean, 37.38).<br />
Natural History.-The rock squirrel occurs over a remarkably wide<br />
clhtic range. Everywhere It is found it is restricted to rocky .habitat.<br />
. . nests are consctructed <strong>of</strong> dry leaves, grass, bark, and pine needles<br />
in burrows under rocks. The animals hibernate from one to six months<br />
per year, depending on elevation and food availability.<br />
There are two breeding periods. In Utah average litter size<br />
was 6.1 (three to nine). Young emerge from the nest at about 56<br />
days <strong>of</strong> age. Rock. squirrels are not particularly social, There is<br />
no dcaninance heirarchy and conrmdcation is poorly developed. Mean<br />
home range is about 0.7 acres, larger for males than for females.<br />
Densities in Utah ranged from 2.3 per acre in spring to 6.1 per acre in fall.<br />
Seeds, nuts, berries, insects, and carrion make up the diet.<br />
The squirrels are sonetimes pests in orchards. Bobcats and badgers<br />
are known to prey on them. This is one <strong>of</strong> our least-studied ground<br />
squirrels. There have been no studies <strong>of</strong> the species in Colorado.<br />
Further study would be interesting, because the rock squirrel<br />
has traits not common in northern ground squirrels; such as two litters<br />
per year and short hibernation,<br />
Selected References. --Johnson (1981) ; Juelson (1970) ; Steiner<br />
(1975).
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