Natural History of the Ground Squirrels of California/Belding Ground Squirrel
Other names.—Belding Spermophile; Bob-tailed Spermophile; Prairie Dog, part; Picket-pin, part; Spermophilus elegans; Spermophilus beldingi; Colobotis beldingi.
Field characters.—A medium-sized, short-tailed, "picket-pin" type of ground squirrel, without side-stripes or other conspicuous markings, but with bright reddish brown back. Length of body alone about 74⁄5 inches, with tail 22⁄3 inches more. (Closely similar to Oregon Ground Squirrel, but smaller and with back reddish brown instead of brownish gray; compare figs. 20a and 20b.)
Description.—Adult in full fall pelage: Sides of head, hind neck, shoulders, sides of body and flanks continuously yellowish brown (numerous fine hairs which are chiefly black, though light-tipped, lend a dusky tone to these areas); a tinge of olive-ochre pervades the lower margins of those areas adjoining the light underparts; eyelids white; whiskers black; ears dusky, finely haired, not tufted; crown of head to nose, tawny-olive; a broad sharply outlined band of bright hazel brown running down middle of back from between shoulders, narrowing to base of tail. Tail short, full-haired, flatfish; above mixed hazel and black, black predominating toward end, where also a well-defined buffy white fringe; under surface of tail conspicuously deep cinnamon-rufous, with subterminal black interval, and buffy white fringe all around. Upper sides of feet buffy white; claws chiefly black, with horn-colored tips; palms naked; soles naked save for sparse hairing from heel halfway to tubercles. Under side of head and neck, and inner sides of fore and hind legs, buffy white; belly cream-color, with lead-color of bases of hairs showing through.
Color variations.—As far as we can see from the series of specimens studied, adults molt but once a year, during July. May and June specimens show clearly the effects of wear and fading, and are grayer, with the mid-dorsal brown area much duller than in the fresh pelage described above. Young not one-fourth grown are like adults in color, but with mid-dorsal area paler, snuff brown, and under side of tail clay color.
Measurements.—Average and extreme measurements, in millimeters, of twenty mature specimens from the Yosemite section of the high Sierra Nevada are as follows: Ten males: total length, 263 (230–280); tail vertebræ, 66 (60–74); hind foot, 44 (41–45.5); ear from crown, 9 (7–11); greatest length of skull, 44.5 (42.2–46.3); zygomatic breadth, 28.0 (26.4–29.5); interorbital width, 10.5 (9.7–11.0). Ten females: total length, 260 (240–288); tail vertebræ, 66 (55–74); hind foot, 43 (40–46); ear from crown, 10 (8–13); greatest length of skull, 44.0 (41.3–46.5); zygomatic breadth, 28.2 (26.7–28.9); interorbital width, 10.4 (9.7–11.0).
Relatively old individuals show greatest size, especially of skull, which also has acquired more conspicuous ridges and sharper angles. Males average a trifle larger than females.
Weights.—Average and extreme weights, in grams, of twenty mature specimens from the Yosemite section of the high Sierra Nevada are as follows: Ten males, 222 (125.5–285.0); ten females, 240 (172–305). Average, in ounces, both sexes, about 8.
The example showing the least weight was fully adult, but was very lean. Like other ground squirrels this species varies greatly in weight according to the amount of fat present. Specimens taken in August and September are, as a rule, fattest.
Type locality.—Donner, Placer County, California (Merriam, 1888, pp. 317–320).
Distribution area.—Higher parts of the central Sierra Nevada (chiefly Hudsonian life-zone), from vicinity of Independence Lake, Nevada County, south to southeastern border of Yosemite National Park in vicinity of Mount Lyell (see fig. 18). Altitudinal range, from 11,800 feet (as on Mt. Conness) down on western flank of Sierras to as low as 8,100 feet (Porcupine Flat, Yosemite Park); on eastern flank to as low as 6,500 feet, at western border of Mono Lake (Mus. Vert. Zool.).
Specimens examined.—A total of 48 from the following localities in California: Nevada County: Independence Lake, 13. Placer County: "Johnson's Pass, High Sierras" [= Summit], 1. El Dorado County: Mt. Tallac, 1. Alpine County: Hope Valley, 4. Mono County: Mono Lake P. O., 1; Farrington's, Mono Lake, 3; Mono Pass, 1; Tioga Pass, 1; Walker Lake, 1. Tuolumne County: Tuolumne Meadows, 8; middle Lyell Canyon, 1; head Lyell Canyon, 5. Mariposa County: Mt. Hoffman, 10,700 ft., 1; Tioga Road, southeast Mt. Hoffman, 3; near Vogelsang Lake, 2; two miles east Porcupine Flat, 1; one mile east Lake Merced, 1.
This species of ground squirrel was named after Lyman Belding, an early resident of Stockton and a naturalist of considerable attainment. Belding found it in the summer of 1885 in the vicinity of Summit, Placer County, and sent a specimen to Dr. C. Hart Merriam, who later (1888) described the species, calling it Spermophilus beldingi.
The most notable thing about the Belding Ground Squirrel is the great altitude of most of the area it inhabits. It is very closely restricted to the alpine meadows of the high central Sierra Nevada. The warmer levels below seem to be just as inimical to its welfare as the cold upper zones certainly are to the other ground squirrels which inhabit the middle slopes or foothills. Reference to our diagram (fig. 23) will show some interesting facts in this regard. We would infer that the Belding Ground Squirrel is the hardiest of all our species as regards ability to endure long and cold winters, though here the habit of hibernation must come importantly into play as tiding it over the extremes.
This squirrel occurs in fair abundance on the preferred portions of its general range, namely, the grassy meadows in the neighborhood of timber line. Individuals rarely occur down as low as the belt of red firs and aspens (Canadian zone) on the west slope of the Sierras, though on the east slope a few do occur down through the Jeffrey pine belt. It is quite strictly an inhabitant of open levels; it is rarely or never seen in the woods or on steep or rocky slopes. Occasionally an individual ascends to the top of some glacier-borne boulder out in a meadow for a look around, but we have yet to observe any greater exploit in climbing.
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| (a) Oregon Ground Squirrel in meadow near Klamath Falls, Oregon. Photographed by H. C. Bryant, May 30, 1914. Note uniform coloration with no indication of a reddish brown patch on back. | (b) Female Belding Ground Squirrel at entrance to burrow; Tuolumne Meadows, Yosemite National Park. Photographed by T. I. Storer, July 27, 1915. Note patch on back rendered photographically nearly black, but which was reddish brown. Compare with a. |
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| (c) Same squirrel as shown in b standing upright in characteristic "picket-pin" attitude. | (d) Sierra Golden-mantled Ground Squirrel or "bummer," feeding on scraps from the camp table. Note the distended cheek. Bullfrog Lake, 10,600 feet, Fresno County. Photographed by J. Dixon, September 1, 1916. |
Fig. 20.
Probably because of the open nature of their forage ground, these squirrels seem exceptionally timid. The shrill cries of alarm greeting the invader of a meadow upon his approach are quickly followed by total disappearance of the animals, at least for the time being. Each individual seems not to wander usually more than a few yards from the mouth of its burrow, so that but a short run intervenes at any moment between it and safety. The tail is held down when running, not elevated nor waved. The gait is rather slow and clumsy, impressing one observer as resembling that of a short-legged dog. "Where the grass is short there is little up-and-down movement of the body shown in running; but in high grass, instead of parting the stalks and pressing them aside as it progresses, the animal advances by a series of jumps each of which carries it up clear of the grass so that it can glimpse about for a possible enemy" (T. I. Storer, MS).
When within but a few feet of the mouth of its burrow and first taking alarm, a squirrel will rise quickly on its haunches and assume the rigid, upright, "picket-pin" posture (see fig. 20c). This usually brings the animal's head well above the grass tops, so that it can get a good view all about. Also it can then be seen a long way, looking in the distance like a tent-stake or picket-pin out on the meadow. During this pose the fore limbs are pressed closely against the body. Sometimes the animal rises still higher, supporting its whole body on its hind feet and using its stubby tail as a prop (C. L. Camp, MS). The fact that the nose is continually twitched up and down, as if the animal were drawing in air, suggests that the sense of smell may be keen and that it may be used to determine the nature of a supposed enemy. If the observer continues his approach the squirrel suddenly deserts its "picket-pin" pose and dashes for its burrow, where it may hesitate a moment on all fours for one final look before diving out of sight.
The voice of this squirrel closely resembles that of the Oregon Ground Squirrel. The usual call of warning consists of a series of from five to eight short shrill whistles uttered in quick succession and weakening toward the last. Females warn their young when foraging abroad with a lower-pitched, double note, or bark, e-chert'. A single note, sirt, is also frequently heard.
The burrows of the Belding Ground Squirrel are generally located in the meadows which form their forage grounds. Sometimes, near timber line, one finds them in the scant gravelly soil between granite boulders, but always in or near patches of the kind of bunch grass occurring at such altitudes. The mounds are rarely conspicuous, and the holes open up to the surface steeply. Often there is no surplus earth at all around the mouths of the burrows, but this condition might be accounted for by the effects of washing from heavy rain or melting snow. Several measurements of burrows gave an average diameter of two inches. The extent of the underground burrow system has only been tested out in one instance (see fig. 21). In this case the burrow was located in a wet meadow, snowbanks melting all about at the time (June 28), and it proved to be shallow, reaching an extreme depth of only about thirteen inches. But blind branches directed downward indicated the probability of greater depth later in the season when the water table had lowered and the soil dried out. The total length of this burrow system, including all its branches, was close to 54 feet.
Fig. 21. Plot of a used burrow belonging to a female Belding Ground Squirrel, as excavated by J. Grinnell and T. I. Storer in a meadow near the Tioga Road, on Snow Flat, 8,700 feet altitude, Yosemite National Park, June 28, 1915.
Main opening of burrow at a (down this the squirrel went when shot, and was subsequently found at c); two other openings at a' and a"; at b and b' blind branches directed downward (the squirrel may have essayed to dig deeper at these points but was discouraged by water); food materials, including lily tubers, in chamber at f; in the enlargement at the point marked nest was an accumulation of dry grass, the remains of an old nest or the beginning of a new one (the young would not have been born for about two weeks); boulder at g bulged out over the portion of the burrow adjacent to it, affording protection to the supposed nest-chamber.
Diameter of burrow, 45 to 65 millimeters; average of several measurements, 52. Average depth beneath surface of ground, about 135 mm. Greatest depth, at b and b', 330 and 270, respectively. Total length of system, about 54 feet.
The burrow system above described belonged to just one squirrel, an adult female, which was found to contain five embryos, the only exact evidence we have as to the number of young to a litter. This was at 8,700 feet altitude, on Snow Flat, Yosemite Park, on June 28. Half-grown young were common on Tuolumne Meadows, 8,600 feet, July 16. Young two-thirds grown have been taken at Independence Lake, Nevada County, 7,000 feet altitude, as early as July 13. Three third-grown young were seen, and one of them photographed (fig. 22), at 6,800 feet altitude near Williams Butte, Mono County, June 28. There is thus probably some variation in time of appearance of the young, with altitude, the animals at the highest levels being born latest in the season. The young are out quite generally by the 15th of July. Only one litter is born each year. On July 31, on Tuolumne Meadows, Yosemite Park, young Picket-pins were out in parties of six mostly, and sat about the mouths of their burrows or foraged in the very near vicinity. When frightened all members of each group darted for their refuge at the same time, crowding into the hole with some difficulty.
Belding Ground Squirrels become very fat in late summer and hibernate regularly; but exact dates of beginning hibernation in the autumn and emerging in the spring are wanting. We do know that they are not averse to running about over the surface of the snow at high altitudes in June, and so probably come out much earlier, and that in one year, 1915, they were still out as late as October 7 in the vicinity of Ten Lakes, Yosemite Park, although a light snowfall had already occurred. They were numerous on the extensive meadows in Tioga
Fig. 22. Third-grown young Belding Ground Squirrel; photographed by J. Dixon, June 28, 1916, near Williams Butte, Mono County.
Pass on September 28. It is evident that, in spite of its more elevated habitat, the Belding Ground Squirrel goes into its winter sleep a full two months later than the Oregon Ground Squirrel.
Like the Oregon Ground Squirrel, the Belding feeds largely on grass stems and blades. An individual has been seen gathering seeds from grass heads, pulling the latter down to its mouth with its fore feet; but it is certainly not the seed-eater that the California and Golden-mantled ground squirrels are. Neither is there evidence that the Belding stores up much food. As with the Oregon species, its cheek-pouches are small (see fig. 13b). At Soda Springs, on Tuolumne Meadows, the Belding Squirrels have been seen foraging like rats about the mule corral.
The enemies of this species of squirrel probably include most of the carnivores of the high mountains. A Mountain Weasel (Mustela arizonensis) has been seen to kill one by biting it through the back of the neck (C. L. Camp, MS).
The Belding Ground Squirrel bears no decided economic importance, save as might be involved in the grass it eats. Its habitat falls only within the summer range of sheep and cattle, and its numbers are nowhere so great as to be likely to reduce the crop of pasture grass to any material extent.