Page:Natural History of the Ground Squirrels of California.djvu/112

690 predators that dig, such as badgers and coyotes. The mouth of the burrow is kept open, and is flush with the surface of the ground; and there is usually no trace of any mound. Sometimes there is a small pile of fresh earth adjacent to a hole, but this is subject to quick dissipation by the winds or the much more infrequent rains. The mouth of the burrow is subtriangular in outline, the flattish base of the triangle horizontal at the bottom. It is not often circular, as with pocket gophers and kangaroo rats, and usually can be recognized accordingly. There is evidence that these squirrels use the burrows of other rodents, too, such as those of wood rats, kangaroo rats, and even badgers. And in places where such retreats are afforded, individuals seem to have their headquarters in the interstices of rock slides. Suffice it to say that in the Antelope Ground Squirrel we do not find a good digger. It takes a temperamentally phlegmatic animal to dig effectively. The "Ammos" are too fidgety.

This species does not live in colonies in the restricted sense in which this term should be used, but the burrows are scattered out pretty evenly over the general territory occupied. There is less of interdependence between the individuals of this species than in most other ground squirrels.

In traveling through their domain one sees few of these ground squirrels as compared with their real numbers. They are adepts at dodging behind bushes, and at eluding observation by skipping off out of sight considerably in advance of the intruder. For example, in a census of animal life taken near Mohave, March 14, 1918, during a three-hour walk, but two Antelope Squirrels were seen, whereas six were found to have been caught in a line of rat-traps during the same length of time. Then, too, the characteristic tracks in the sand on a quiet day after it has been laid by a norther leave a graphic record of the multitudinous peregrinations of these active rodents. They can make more tracks in a given length of time than any other mammal with which we are acquainted!

Some notes made by the senior author the second week of March, 1918, near Mohave will help to give a clear idea of the characteristics of the animal under discussion. Nearly all individuals seen would run very fast across open spaces between the bushes, but would hesitate a moment or so when passing through the bushes. When approaching its burrow each animal would stop stock still just short of the mouth of the burrow, and watch the intruder intently with head turned to one side sufficiently so that it could look back past its rump. Meanwhile the tail was vibrated intermittently as usual. Presently the animal would dive down out of sight. One was seen to go down into a hole situated in the side of a mound of sand accumulated about the base of a very large creasote bush. This hole was one yard from the nearest upright stem, but was directed downward diagonally toward the root-system, and it was overshadowed by the radiating branches. The diameter of this burrow at its mouth was just 40 millimeters (about one and three-fifths inches). The last that was seen of another squirrel as he dived for his burrow, he had his tail over his back twitching as violently as ever. He, too, had hesitated just an instant before the final plunge.