Natural History of the Ground Squirrels of California/Death Valley Round-tailed Ground Squirrel
DEATH VALLEY ROUND-TAILED GROUND SQUIRREL.
Citellus tereticaudus eremonomus Elliot.
Other names.—Death Valley Spermophile; Citellus eremonomus.
Field characters.—Exactly as for the Yuma Round-tailed Ground Squirrel.
Description.—As for the Yuma and Palm Springs Round-tailed Ground Squirrels, but coloration decidedly darker than in either, near wood brown. This feature is characteristic in all of the eight skins of eremonomus at hand.
Color variations.—The time of the spring molt is indicated by a specimen of date April 10, in which new summer pelage shows on the head and rump; an example of May 3 is in absolutely new summer pelage except, of course, for the tail. One specimen has a bobbed tail, with an abnormal tuft of hairs at the end, showing conspicuously a band of black and then a terminal band of white. Most of the skins show a curious spotting of the rump which is clearly not due to color markings on the hairs, but to places where hairs are absent, so that the dark-colored skin and dark bases of adjacent hairs show through. These may indicate scars from insect bites.
Measurements.—Average and extreme measurements, in millimeters, of eight adult female specimens from Death Valley are as follows: total length, 249 (240–255); tail vertebræ, 91 (87–93); hind foot, 35 (34–36); ear from crown, 2.1 (2.0–3.0); greatest length of skull, 36.0 (34.8–36.6); zygomatic breadth, 22.5 (22.0–23.4); interorbital width, 8.7 (8.3–8.8). No males are available.
Weights.—Average and extreme weights, in grams, of eight adult females from Death Valley are as follows: 144.3 (121–158). The average, in ounces, is 5.1.
Type locality.—Furnace Creek [Ranch], Death Valley, Inyo County, California (Elliot, 1903, p. 243).
Distribution area.—Floor of Death Valley, in Inyo County. Life-zone, Lower Sonoran. Only known locality of occurrence, vicinity of Furnace Creek Ranch (Greenland Ranch), -240 to -175 feet altitude. Apparently cut off from its nearest relative, tereticaudus proper, by the elevated rim of the Death Valley basin.
Specimens examined.—A total of 8, all from the near vicinity of Furnace Creek Ranch, -178 feet. Death Valley, Inyo County.
As far as known, this race of Round-tailed Ground Squirrel is limited in its distribution to the bottom of the deep sink known as Death Valley, and even there to the belt of mesquites immediately around the margin of the alkali flats at the lowest level. The entire habitat of this Death Valley subspecies thus lies below sea level, a distinction probably not shared by any other rodent in America.
Our experience with this squirrel was obtained during April and early May, 1917, in the immediate vicinity of old Furnace Creek Ranch, now known as Greenland Ranch. The animals at the time of our visit were not invading the cultivated land, though we were assured by the foreman that they had come into the alfalfa fields in previous seasons. Since this was the type locality of the subspecies, special efforts were made to obtain a series of specimens. The animals were not abundant, and proved practically impossible to trap. Shooting was resorted to, though with but little better results. The following notes were made on April 10 by the senior author while hunting them.
During a two hours hunt at midday at least five individuals were heard on the mesquite-crowned sand dunes within a mile southwest of the ranch. The warmth had seemingly brought them out, for the previous two or three days had been relatively cool, and none had been seen. A temperature of over 100° in the shade seemed to be necessary to bring the animals out into full activity. "I caught sight of one standing upright at the mouth of its burrow, squeaking, and of two others running over the sand beneath the trailing green mesquite branches. The lines of footprints in the sand centering at the mouths of their burrows are diagnostic. The animals are extremely shy, going below ground at the slightest alarm. By standing ten minutes or so 'at attention' about fifteen yards from the mouth of a burrow down which one vanished, I finally saw the top of its head reappear to the level of its eyes. This position was maintained for many minutes, until the animal suddenly raised its whole head and neck into view, when I shot it.
"Later, while I was lying prone on the sand under a mesquite, one came up to within eight feet of me and gave its shrill, wiry cry, or squeak. A mere movement on my part, and it vanished, quick as thought." It was found that a little "screeping" (lips to back of hand) would often bring one of the squirrels stealthily investigating through the brush, provided the observer kept perfectly motionless himself and was possessed of patience. The squirrel would sometimes squeak, apparently in answer, and thus be called into very close "aux" range. The burrows were as a rule located in the periphery of a large mesquite clump, where they were shaded by the radiating leafy branches which trailed down the sandy slopes. Not more than three burrows certainly of this rodent were to be found about any one clump.
The mesquites during early April were just coming out into full new foliage. The stomachs of the squirrels shot were distended with masses of finely chewed mesquite leaves and nothing else. This, in fact, was absolutely the only kind of vegetation anywhere in sight for hundreds of yards. In one instance the total weight of the freshly killed animal was found to be 154.5 grams; of the full stomach alone, 28.7 grams, or 19 per cent (near one-fifth) of the total weight. In other words, a Death Valley Round-tailed Ground Squirrel may eat close to one-fourth its own weight of green mesquite leaves.
No young were seen by us up to the time of our departure, but they are probably born about the first of May. Two old females captured April 10 and 12 contained four and three embryos, respectively.