Natural History of the Ground Squirrels of California/Los Baños Antelope Ground Squirrel
LOS BAÑOS ANTELOPE GROUND SQUIRREL.
Ammospermophilus nelsoni amplus Taylor.
Other names.—Nelson Ground Squirrel, part; Antelope Chipmunk, part; Ammospermophilus nelsoni, part.
Field characters.—Exactly the same as for the Nelson Antelope Ground Squirrel.
Description.—General coloration in all pelages exactly as in nelsoni proper, but clay color of upper surface a trifle paler, more buffy, and white side-stripes less distinct. Size somewhat greater, especially as regards ears.
Measurements.—Average and extreme measurements, in millimeters, of twenty full-grown specimens from twenty miles south of Los Baños, in western Fresno County, are as follows: Ten males: total length, 246 (234–253); tail vertebræ, 73 (66–75); hind foot, 41 (40–43); ear from crown, 7.8 (7.0–9.0); greatest length of skull, 41.8 (41.0–42.7); zygomatic breadth, 24.8 (24.0–26.2); interorbital width, 10.1 (9.4–10.4). Ten females: total length, 236 (230–243); tail vertebræ, 73 (67–78); hind foot, 40 (37–43); ear from crown, 7.7 (6.5–9.0); greatest length of skull, 41.2 (39.8–42.0); zygomatic breadth, 24.3 (23.5–25.5); interorbital width, 10.0 (9.2–10.3).
Comparison with the measurements given for nelsoni will show that amplus is decidedly larger, with especially larger ear.
Weight.—Only one record of adult weight is available, that of an old male, 186.3 grams (6½ ounces).
Type locality.—Twenty miles south of Los Baños, Merced County [really near mouth of Little Panoche Creek in Fresno County], California (Taylor, 1916, p. 15).
Distribution.—Known as yet only from a limited section of the floor of the San Joaquin Valley within 35 miles south of Los Baños, in southwestern Merced County and northwestern Fresno County. Life-zone, Lower Sonoran.
Specimens examined.—A total of 34 from the following localities in California. Merced County: Sweeney's ranch in hills "22 miles south of Los Baños," 2. Fresno County: mouth of Little Panoche Creek, 18 or 20 miles south of Los Baños, 29; Hayes Station, B. M. 502, on Panoche Creek, 19 miles southwest of Mendota, 2; one mile east of Mendota, 1.
The Los Baños Antelope Ground Squirrel very closely resembles the Nelson Squirrel, and is doubtless practically identical with that form in general habits and locality preferences. More thorough exploration will probably show that the distribution of the two is continuous, in other words that the Los Baños race has resulted from a northward extension of the ancestral stock which has allowed the acquisition of the slight differences of greater size and paler tone of coloration which characterize amplus.
Along the western rim of the San Joaquin Valley south of Los Baños this subspecies is common locally. The type series was taken by R. H. Beck June 20, 1912, near the mouth of Little Panoche Creek, where the animals were found occupying holes on common territory with California Ground Squirrels. In one instance a "chipmunk" was shot at the same hole with a "ground squirrel."
Near the point where Panoche Creek breaks out of the hills, a few miles farther south, the last of June, 1918, museum collectors found a few Antelope Squirrels along roads between barley fields. The cheek-pouches of the two shot at the edge of such a field were full of barley grains. The breeding season on both the above dates was long passed; young were nearly or quite full-grown. Remains of Ammospermophilus were found about the mouth of the burrow of a kit fox, evidence of the identity of one kind of enemy.
The sort of country inhabited by this Ground Squirrel is arid and as yet to but a small extent under cultivation. Water is not available for extensive irrigation. The economic status already set forth for the Nelson Squirrel probably also holds for the Los Baños race.