Natural History of the Ground Squirrels of California/Inyo Golden-mantled Ground Squirrel
INYO GOLDEN-MANTLED GROUND SQUIRREL.
Callospermophilus chrysodeirus perpallidus Grinnell.
Other names.—Sierra Golden-mantled Ground Squirrel, part; Yellow-headed Chipmunk, part; Callospermophilus chrysodeirus, part; Spermophilus chrysodeirus, part; Citellus chrysodeirus, part.
Field characters.—Exactly the same as for the Sierra Golden-mantled Ground Squirrel, save for pallor of coloration.
Description.—Adult in fresh late-summer pelage: Pattern of coloration and chief features throughout precisely as in the Sierra Golden-mantled Ground Squirrel, but general tone of coloration paler; middle of back, rump and sides tending towards ashy, head less richly coppery, and under surface of body and upper surfaces of feet whiter; under surface of tail medially ochraceous-tawny. Because the lighter colors are paler in tone, the jet black side-stripes stand out with greater sharpness than in the Sierran race.
Color variations.—As in the Sierra Golden-mantled Ground Squirrel. In some specimens in fresh pelage the throat is pure white without a tinge of buff. Half-grown young just out of their nest-burrows show the characteristic paleness of their subspecies to as great a degree as adults in new coat. The pallidness of the adults in old worn breeding dress is greater in degree than in the Sierran race, evidently due to the greater bleaching effects of the more intense sunlight and dryness to which the Inyo animals are exposed. The innate paleness of the Inyo race is thus accentuated by external factors.
Measurements.—Average and extreme measurements, in millimeters, of twenty full-grown specimens from the White Mountains, Mono and Inyo counties, are as follows: Ten males: total length, 268 (260–279); tail vertebræ, 92 (80–105); hind foot, 40 (38–43); ear from crown, 13.4 (11.0–15.0); greatest length of skull, 42.9 (42.0–44.0); zygomatic breadth, 26.2 (25.0–26.9); interorbital width, 10.0 (9.0–11.3). Ten females: total length, 264 (254–286); tail vertebræ, 85 (78–89); hind foot, 38 (36–42); ear from crown, 13.3 (10.0–16.0); greatest length of skull, 41.4 (39.6–42.3); zygomatic breadth, 25.9 (25.0–26.6); interorbital width, 9.8 (9.3–10.2).
As will be seen from the above measurements in comparison with those given for the Sierran race, there are no important size differences between perpallidus and chrysodeirus; indeed it seems likely that, with large enough series, such discrepancies as are here in evidence would disappear altogether. The same variations due to age and sex seem to be present.
Weights.—Average and extreme weights, in grams, of twenty full-grown specimens from the White Mountains, Mono and Inyo counties, are as follows: Ten males, 182 (166.5–199.5); ten females, 160 (141.0–209.1). Averages, in ounces: males, about 6½; females, about 5½.
There were no gravid females in this lot. All were taken before August 10 and so none had become very fat. These facts may account for the lesser weights than shown for the Sierran race.
Type locality.—White Mountains at 10,300 feet altitude, near Big Prospector Meadow, Mono County, California (Grinnell, 1918, p. 429).
Distribution area.—The upper portions of the arid mountain ranges of extreme eastern California lying east and north of Owens Valley, namely the Inyo and White Mountains, and the mountain mass lying southeast of Mono Lake. Northernmost station, Mono Craters, Mono County (Mus. Vert. Zool.); southernmost, summit of Inyo Mountains east of Lone Pine (Elliot, 1904, p. 288). Along this extent of territory the distribution of the animal is not continuous but is interrupted at the lowermost gaps between the Inyo and White Mountains and at the extreme head of Owens Valley. Zonally, this race belongs to Boreal, but it extends down locally as low even as Upper Sonoran (see fig. 23). In other words, it extends from above timberline down to as low as 7,000 feet altitude (lower edge of piñons), the latter level for it being recorded from the bottom of Silver Canyon east of Laws. The highest observed station of occurrence is McAfee Meadow, 11,600 feet, near White Mountain Peak (Mus. Vert. Zool.).
Specimens examined.—A total of 50, from the following localities in California: Mono County: Mono Mills, 4; Mono Craters, 1; McAfee Meadow, White Mts., 7; Big Prospector Meadow, White Mts., 22; Cottonwood Creek, White Mts., 1. Inyo County: Roberts Ranch, Wyman Creek, White Mts., 2; Silver Canyon, White Mts., 4; Black Canyon, White Mts., 5; Mazourka Canyon, Inyo Mts., 4.
This is simply a pale desert-range race of Golden-mantled Ground Squirrel, probably cut off but incompletely from its near relative, chrysodeirus, of the Sierra Nevada. There can hardly be expected to be any decided differences in habits between the two; yet the different "setting" of perpallidus—exceedingly dry, rocky slopes, with only sparse timber at best—has left in our minds an impression of distinctness. This only goes to show that we cannot conveniently, nor should we properly (from a scientific standpoint), consider any animal altogether apart from its normal surroundings.
In the Inyo Mountains this squirrel was found by H. S. Swarth (MS) to range from the level of the lowest piñons in Mazourka Canyon, about 7,500 feet altitude, to the highest summit visited by him, 10,500 feet. In the White Mountains, east of Laws, the senior author found it to range down Silver Canyon to as low as 7,000 feet altitude, and here this and the Antelope Ground Squirrel of the lower country overlapped in their ranges to a small degree. The "Callos," in such precipitous canyons as Silver Canyon, were essentially "rock" squirrels, in that they had their retreats in the slides of shale rock at the bases of the cliffs and even in the broken rock outcrops far up the canyon walls. Through and along these they clambered, a bit clumsily perhaps, but without loss of foothold so far as was seen.
Higher up, on the lofty rolling plateau forming the summit of this mountain range, the Golden-mantled Ground Squirrels were extremely abundant along the edges of the stunted forests of foxtail and lodgepole pines, and even far from timber out on the sagebrush flats, but in the latter locations there were always near at hand fractured granite outcrops which afforded safe retreats. Where there were grassy meadows the animals foraged all over them. It occurred to the observer that here in the White Mountains there was but this one species of ground squirrel and that it therefore had the run of the whole place, as it were, without meeting with any competitor, as is the case in the Sierras and elsewhere. This would account for the facts as observed, namely, that in the White Mountains the Copperheads were extraordinarily abundant and ranged widely into all sorts of associations.
Our lines of rat-traps baited with rolled oats brought in many "Callos," even youngsters but a third grown, and it was practically impossible to keep steel traps set during the day, as the bait, consisting of the bodies of the various birds and small mammals prepared for specimens, seemed to be especially attractive to the squirrels. Wherever the traps were set, they would be searched out and unwittingly sprung as the squirrels scrambled over them in quest of the bait. It seemed impossible that the "Callos" could have located some of the settings except through scent, and it is reasonable to suppose that the sense of smell is employed not only in seeking meat but when searching for the bulbs of certain plants.
Young were out in numbers the last week of July at the 10,000-foot level, being then one-third to one-half grown. Lower down, in Black Canyon at 8,000 feet altitude, half-grown young were seen on July 5 (1917); and at 10,500 feet altitude, on Cottonwood Creek, third-grown young were noted on August 8. This shows the usual variation of appearance of young with altitude, which of course has to do with advance of the season, and so with temperature.
In Mazourka Canyon, Inyo Mountains, two females, each containing six embryos, medium-sized and small, respectively, were taken May 19 and 22 (1912). We found no evidence of litters of a larger number than six; and there is certainly no more than one litter per year.