Page:The Common Ground Squirrels of California.djvu/3

 UNIVERSITY OF CALIFORNIA


 * COLLEGE OF AGRICULTURE
 * BERKELEY, CALIFORNIA

(, 1912.)

THE COMMON GROUND SQUIRRELS OF CALIFORNIA

H. C. BRYANT.

Two rodents in the State of California give the rancher more trouble than all the other animal pests combined, insects excepted. One, the pocket gopher (Thomomys sp.), feeds largely on the roots of plants and trees and hence is one of the worst pests of the garden and orchard. The other, the ground squirrel (Citellus sp., Ammospermophilus sp., Callospermophilus sp.) is especially destructive to grain, but it is also destructive to nuts and fruit. The established fact that the California ground squirrel is instrumental in spreading bubonic plague has made these animals of more than ordinary economic importance. These two principal rodent pests are easily distinguished by their general appearance, size, habits, and burrows. The pocket gophers have very short ears, small eyes, short tails, and cheek pouches which open externally; they are relatively small (6 to 10 inches), largely nocturnal, and live almost entirely in their burrows. Ground squirrels have relatively large ears and eyes, longer tails, and the cheek pouches do not open externally ; most of them are larger in size, diurnal, and forage for food above ground. The burrow of the pocket gopher can be distinguished by a mound of earth surrounding the entrance, and by the fact that the opening is nearly always kept plugged full of earth. The burrow of the ground squirrel on the other hand is usually open, with the excavated earth thrown out on one side of the entrance only. One or more runways lead away from the burrow.

According to Merriam, the ground squirrels of California may be arranged in four groups: (a) the large, long-eared gray ground squirrel (subgenus Otospermophilus) (b) the small, short-eared, brownish species (genus Citellus); (c) the small, white-striped, antelope ground squirrel of the deserts (genus Ammospermophilus) (d) the golden-mantled ground squirrel of the mountains (genus Callospermophilus).

The "digger" ground squirrels (Citellus sp.), which belong to the subgenus Otospermophilus, are not only the most destructive, but are the disease carriers (Fig. 1). These ground squirrels usually live in colonies, their burrows often being connected for a considerable distance. Food in the shape of grain, seeds, and fruit is stored for the winter season. The call note is a single loud whistle. The warning note is a similar short whistle followed by two or three chattering trills. Young, numbering from five to ten, are usually born in March and April. This ground squirrel has been found infected with bubonic plague, and several cases of human plague have been traced to a bite