Natural History of the Ground Squirrels of California/San Bernardino Golden-mantled Ground Squirrel
SAN BERNARDINO GOLDEN-MANTLED GROUND SQUIRREL.
Callospermophilus chrysodeirus bernardinus (Merriam).
Other names.—San Bernardino Ground Squirrel; San Bernardino Spermophile; Yellow-headed Chipmunk, part; Spermophilus bernardinus; Spermophilus chrysodeirus brevicaudus; Citellus chrysodeirus bernardinus; Callospermophilus bernardinus; Tamias chrysodeirus brevicaudus; Tamias lateralis, part.
Field characters.—The same as for the Sierra Golden-mantled Ground Squirrel. The slight shortness of tail characterizing this race is certainly not a sufficient difference for notice at any distance.
Description.—In all pelages: Coloration, as far as we can see after comparing large series of specimens, exactly as in the Sierra Golden-mantled Ground Squirrel. None of the paleness is apparent such as characterizes the Inyo race.
Variations.—Of the same sort as discussed under the Sierran race.
Measurements.—Average and extreme measurements, in millimeters, of twenty full-grown specimens from the San Bernardino Mountains are as follows: Ten males total length, 260 (240–278); tail vertebræ, 80 (68–90); hind foot, 40 (36–43) greatest length of skull, 43.5 (42.0–45.6); zygomatic breadth, 26.6 (25.5–27.6) interorbital width, 10.7 (10.1–11.3). Ten females: total length, 251 (236–271) tail vertebræ, 78 (72–86); hind foot, 38.5 (35–42); greatest length of skull, 41.8 (40.4–43.0); zygomatic breadth, 25.5 (24.2–26.8); interorbital width, 10.2 (9.7–10.8).
Unfortunately, ear measurements from fresh specimens are not available; but dried skins look to have decidedly smaller ears than in either the Sierra or Inyo race, this character being especially noticeable in the young. It will be noted from the above measurements in comparison with those given for chrysodeirus and perpallidus, that the body size of bernardinus is just the same as in the others, while the tail length is decidedly less. This, then, is the character of the subspecies bernardinus, shortness of tail; and it shows up well in a series of specimens, even very young ones. However, this difference in tail length between adults of bernardinus and of chrysodeirus averages but somewhat less than half an inch, and individual variation brings overlapping in a certain proportion of specimens. In other words, an extra short-tailed chrysodeirus might even have a longer tail than an extra long tailed bernardinus. The race bernardinus is but slightly and incompletely differentiated.
No weights are available for this subspecies.
Type locality.—San Bernardino Peak, San Bernardino Mountains, San Bernardino County, California (Merriam, 1893, p. 134).
Distribution.—Restricted to the relatively small area, not more than twenty-five miles in greatest width, comprised in the higher parts of the San Bernardino Mountains (see fig. 24). Belongs to the Boreal zone and upper part of the Transition. Extends up to the very summit of San Gorgonio Peak, 11,485 feet altitude, and down locally, as near Bear Lake, to 6,700 feet (Grinnell, 1908, p. 141).
Specimens examined.—A total of 84, from the following localities, all in San Bernardino County, California: San Gorgonio Peak, 2; Dry Lake, 3; South Fork of Santa Ana River, 14; Sugarloaf Mountain, 2; Bluff Lake, 61; Bear Valley, 2.
Far separated by desert and lowland from the habitat of its near relative on the Sierras, the Golden-mantled Ground Squirrel of the San Bernardino Mountains has developed slight peculiarities which make it recognizable as a distinct race. It has the most restricted range, probably, of any species or subspecies of ground squirrel in the state. It seems strange that it should be wholly lacking as an inhabitant of the San Gabriel and San Jacinto mountains, so near by on either hand and seemingly of quite similar environment to the San Bernardinos. On the higher parts of the San Bernardino Mountains it is certainly not on the wane, but thrives greatly, perhaps outnumbering all the other members of the squirrel family put together.
In July, 1905, we found the Golden-mantled Ground Squirrels especially numerous around Bluff Lake, altitude 7,500 feet. Here they were to be seen all over the floor of the pine and fir woods, foraging among the chinquapin and deer-brush thickets. None was ever seen to climb a tree, though individuals were often seen perched motionless on stumps, logs or boulders. No matter where encountered, they always sought safety in holes in the ground or in crevices among rocks. They were notably quiet animals, giving only occasionally a single sharp note of alarm, or else, rarely, a low chuckle.
Fig. 25. San Bernardino Golden-mantled Ground Squirrel as taken from nest while dormant during period of hibernation. Note that the animal is curled into an almost globular shape, with head down and nose snuggled against stomach between fore and hind feet; tail curled underneath, partly concealing head.
Around Bear Lake the Yellowheads were common through the woods down to the water's edge. On the north slopes of Sugarloaf, on August 22, they were very busy gathering cheek-pouchfuls of seeds of a lupine, and the fruits of the deer-brush (Ceanothus cordulatus) and of a recldish-fruited currant (Ribes sp.). Elsewhere they were seen carrying to their burrows quantities of the green burrs of the chinquapin (Castanopsis sempervirens) . The burrows usually opened out under logs, rotten stumps, or boulders. There was seldom any mound of earth to mark an entrance.
A female squirrel captured at Dry Lake, 9,000 feet altitude, on June 22, was found to contain four embryos. The young must have been born generally during the early part of July, in a few eases as late as early August, to judge from the relative sizes of the young seen abroad. The first to appear aboveground were noted on July 17 at Bluff Lake. These were about one-third grown and seemed quite able to forage independently of their parent. The latter paid no attention whatever to them, only giving the sharp alarm note if an intruder was sighted.
Two young ones trapped alive were taken home to Pasadena and kept in a cage. Early in the autumn one killed the other. The remaining individual survived for three years, latterly inhabiting a rock-pile in the yard and ranging freely where he would. Each winter he spent about seven months, October to April, inclusive, in hibernation (see fig. 25), with only occasional periods of activity for a day or two during spells of warm weather. It is interesting to note that this inclination to lie dormant was thus shown strongly at the low altitude of Pasadena, where the winter temperature scarcely ever reached the freezing point. There could have been no practical reason for it as regards failure of food, for a supply was always provided the animal in abundance. The annual program seems to require the dormant period, and this comes on at a regular time, and lasts the usual period, whether or not it happens to be essential to the survival of the individual. It is an inherited trait of the race.