Natural History of the Ground Squirrels of California/Mohave Ground Squirrel
YUMA ROUND-TAILED GROUND SQUIRREL (AT LEFT). MOHAVE GROUND SQUIRREL (AT RIGHT).
Other names.—Mohave Desert Spermophile; Mohave Desert Ground Squirrel, part; Spermophilus mohavensis; Citellus tereticaudus mohavensis, part.
Field characters.—A small-sized, brown-colored ground squirrel, without stripes or special markings whatsoever on the body, but with short broadly haired tail, white underneath; ear a mere rim; length of body alone, about 6½ inches, with tail about 2½ inches more.
Description.—Adult in full winter pelage: General tone of whole upper surface from nose to base of tail cinnamon drab; hairs on back when examined closely are seen to be lead-color at base, then ashy white, then army brown, and tipped with white; mixed with these hairs are a few of solid black color, and on the rump some which are black with a white interval near end. Eyelids white, but cheeks like back; rim of ear and upper sides of feet tinged with light pinkish cinnamon; palms of fore feet naked; soles of hind feet clothed with long buffy hairs; claws black with horn-colored tips. Under surface of body silvery white, but slaty bases of hairs show through making the general effect light gray. Under surface of the flattish stubby tail pure white; upper side like back at base, becoming mixed black and white toward end; extreme end with white fringe. Adult in summer pelage: Coat very much coarser and shorter than in winter; general color tone browner, close to cinnamon, but a grizzling effect is produced by white hair-tippings everywhere on upper surface. Sides of face paler than in winter, and lower surface of body pure white, owing to lack of lead-color at bases of individual hairs.
Color variations.—Specimens of dates May 3 and 12 are in process of molt from winter to summer pelage. Patches of worn and yellowed winter hairs remain on the fore back and rump. The tail is seemingly not included in the spring molt, and the old tail hairs become crinkled and broken at the ends; the white of the under side is dingy, and a dark subterminal band around the end of the tail shows through.
Measurements.—Average and extreme measurements, in millimeters, of seven adult specimens (5 males, 2 females), from the northern part of the Mohave Desert are as follows: Total length, 224 (212–230); tail vertebræ, 62 (42–72); hind foot, 36 (34–37); greatest length of skull, 38.6 (38.1–39.0); zygomatic breadth, 24.3 (23.6–25.3); interorbital width, 8.7 (8.2–9.2).
The two sexes appear to be alike in measurements as well as in coloration.
Weights.—An adult male, not particularly fat, was found to weigh 104 grams (about 3⅔ ounces).
Type locality.—Mohave River, California (Merriam, 1889, p. 15). More exactly, near Rabbit Springs, about 15 miles east of Mohave River at Hesperia, in San Bernardino County (Stephens, in conversation, January 1, 1916).
Distribution area.—Not continuous; western parts of the Mohave Desert, from Haiwee, Inyo County, south to Rabbit Springs, San Bernardino County (see fig. 18). Life-zone, Lower Sonoran, though only in its upper portion apparently. Altitudinal range, 2,500 to nearly 4,000 feet.
Specimens examined.—A total of 8, from the following localities in California: Inyo County: Haiwee Meadows, 3,750 feet alt., about ten miles south of Owens Lake, 2 (in coll. U. S. Biol. Surv.); Little Lake, 3,100 feet, 2 (Mus. Vert. Zool.). San Bernardino County: Salt Wells Valley (eastern edge near Inyo County line), 2,500 feet, 3 (U. S. Biol. Surv.); Rabbit Springs, 2,900 feet, east of Mohave River, 1 (in coll. F. Stephens).
The Mohave Ground Squirrel, although first discovered in 1886 by Mr. Frank Stephens of San Diego, has remained about the least known of all our rodents. Only four rather scattered localities of occurrence are definitely known, as listed above under "Specimens examined." The dates represented are March 22 and 24, May 3 and 12 and June 5. The two specimens in the Museum of Vertebrate Zoology were trapped on the first two specified dates, in 1918, on the hillsides immediately west of Little Lake. They were daytime-taken in oat-baited rat-traps set beneath creasote bushes on gravelly ground. In spite of diligent search by the collectors everywhere in the neighborhood, not one of this species was seen alive. No information is available to us in regard to either behavior or food.
This ground squirrel is altogether distinct from Citellus tereticaudus. There is no indication of intergradation with that species, as stated by Elliot (1904, p. 291). In fact, the animals reported by that author from Daggett were all probably in reality tereticaudus, which species is known to us to be present at Daggett. The tail of mohavensis is always much shorter and more broadly haired than in tereticaudus, the claws are stouter, the cheeks are brownish instead of white, the under side of the tail is white, instead of buffy with brown mottlings toward the end, the quantity of winter pelage is greater, and the general tone of coloration is always decidedly dark.
The fact that the under side of the tail is white, as in the Antelope Ground Squirrel, leads us to suspect some such special habit of displaying this member as is possessed by the latter animal. But this is mere speculation. The relationships of mohavensis as indicated by structural features are thought to lie rather with Citellus than with Ammospermophilus.