white-tailed prairie dog
Range: Western Colorado and eastern Utah to central Arizona and New Mexico.
Habitat: Grassy meadows and mountain parks mainly in the Transition Life Zone although they are often found both above and below this area.
Description: A ground-dwelling rodent somewhat resembling a ground squirrel but several times larger than the biggest species of that genus. Total length 12½ to 15 inches. Tail 2¼ to 2½ inches. Weight 1½ to 2½ pounds. Color buff to cinnamon buff, the short fully-haired tail tipped with white. Sides of face darker with a dark area over the eyes. Legs, feet, and underparts pale cinnamon buff. Young, usually five in number, born in early summer.
Cynomys gunnisoni is the representative species of the western group of prairie dogs. The two remaining of the group, Cynomys leucurus and Cynomys parvidens, both white-tailed species, are very similar and possibly will be classified with Cynomys gunnisoni in the future. Cynomys leucurus is found in northwestern Colorado and northeastern Utah, while Cynomys parvidens is native to mountainous valleys in central Utah.
The common name “white-tailed prairie dog” is usually applied to Cynomys gunnisoni, the most widely distributed member of the race. The range of this species borders on but seldom overlaps that of the black-tailed prairie dog which lives farther east and at lower elevation. Climatic and geographic barriers separating these two races are largely responsible for pronounced differences in their habits. Prairie dogs are gregarious creatures, perhaps more so than any other rodent. Formerly the black-tail species inhabited countless thousands of acres in the Great Plains region. A single colony might occupy an area several miles in diameter and number many thousands. On this relatively flat land, every home site was equally advantageous and the grass and herbage all ideally suited to the prairie dog’s use. Periodic flooding of their burrows on these level prairies was avoided by building conical mounds with a rim of earth around the entrance. This ingenious practice, simple though it seems, represents a long step in the adaptation of these animals to their environment.
White-tailed prairie dogs, on the other hand, are limited to the narrow valleys and infrequent open meadows of the mountains. Here there is neither room nor food to maintain the huge colonies characteristic of the black-tailed. Under these conditions the number of individuals in a town will vary from a few to 200, seldom more. If the town becomes crowded, many of the inhabitants may migrate to some more favorable location. This sometimes entails a trip of several miles, a hazardous undertaking for a small animal whose only escape from large predators is in an underground burrow.
Food of this mountain prairie dog is varied. The standard diet of grass and roots is augmented with browse, bark, and tubers. Bulbs of mariposas are taken wherever available. Coarse-leaved annuals such as sunflowers are not passed by. In addition to this vegetable diet, worms, beetles, and larvae as well as mature forms of most insects are eaten whenever possible.
Burrows of white-tailed prairie dogs, though comfortable, are not made with the painstaking care found in those of the lowland species. There is no need for a conical mound or built-up rim because there is virtually no drainage problem on the sloping terrain of the mountains. Naturally the burrows will not be excavated in the path of flood waters, but on higher ground. Earth brought out from the underground workings is piled to one side or in front of the entrance. The mound thus formed is used as a place to sun bathe or, even more important, as a look-out post from which to see all that goes on. Because these small colonies do not have the advantage of numbers, each individual must be especially alert to approaching danger. Burrows often have more than one entrance, each with its well-packed sentry post at hand, the underground plan is simple. It consists of a more or less vertical shaft from which one or more tunnels extend horizontally. It is common supposition that the prairie dog digs deeply enough to strike water. This is not so; many burrows do not go deeper than 6 feet. In any event, they penetrate just far enough to insure a comfortable average temperature in both summer and winter. Water requirements of prairie dogs are met largely by the succulent nature of their food. It is also presumed that during late summer months when the diet consists to some extent of seeds, a chemical process within the system transforms some of the starches to water.