Natural History of the Ground Squirrels of California/Fisher Ground Squirrel
Other names.—Fisher Spermophile; Digger Squirrel, part; Spermophilus beecheyi, part; Spermophilus beecheyi fisheri; Spermophilus grammurus fisheri; Citellus variegatus fisheri; Citellus grammurus fisheri; Otospermophilus beecheyi fisheri; Spermophilus grammurus beecheyi, part.
Field characters.—As for the Beechey Ground Squirrel, differing in paler tone of general coloration, and in more extensive and purer white shoulder patches. Length of body alone about 9¾ inches, with tail about 6 inches more.
Description.—In all pelages: Closely like beecheyi, except for pallid tones of color predominantly light cinnamon-drab, and extension of light areas. The shoulder patches in typical fisheri are much clearer white and tend to meet on the fore back between the shoulders; in some specimens the mid-dorsal grayish brown stripe is almost obliterated by these white invasions. The back of the ear is usually grizzled buffy in fisheri instead of chiefly black, and its hinder margin and base are silvery white. The lower surface of the body and the upper surfaces of the feet are usually much whiter, less buffy, than in beecheyi.
Color variations.—The range of individual and seasonal variation in fisheri seems to be about the same as in beecheyi.
The extreme of the characters of fisheri are developed in the Inyo region, and gradual intergradation or blending takes place towards beecheyi chiefly through southern Tulare aud Kern Counties. The dotted line on the map (fig. 17) separating the ranges of fisheri and beecheyi represents no place of abrupt demarcation but only somewhere near the middle of the belt of intergradation. Many individuals from the vicinity of this hypothetical line are so nearly betwixt typical beecheyi and typical fisheri that they can only arbitrarily be placed under one name or the other. This has been done with such intermediate examples in the lists of specimens examined.
Measurements.—Average and extreme measurements, in millimeters, of thirteen mature specimens from Inyo County are as follows: Five males: total length, 417 (400–455); tail vertebræ, 163 (155–180); hind foot, 57 (50–65); ear from crown, 19 (16–22); greatest length of skull, 55.4 (54.1–57.0); zygomatic breadth, 34.7 (33.3–36.3); interorbital width, 13.3 (13.1–13.9). Eight females: total length, 396 (374–417); tail vertebræ, 157 (145–170); hind foot, 53 (51–55); ear from crown, 19 (18–23); greatest length of skull, 53.9 (52.3–55.7); zygomatic breadth, 33.2 (31.0–34.7); interorbital width, 13.2 (12.2–14.3).
The above figures show that the race fisheri is decidedly smaller in almost every particular than beecheyi. The disparity between the sexes is quite as well shown, however, and the rest of the variable features seem to be exhibited in about the same degree, making due allowances for the smaller number of fisheri measured.
Weights.—Average and extreme weights in grams of eight mature specimens from Inyo County are as follows: Five males, 589 (480–656); three females, 400 (321–440). Averages in ounces: males, about 20¾; females, about 14.
It is probable that a larger series of weights would give somewhat different averages. That for the females seems low.
Type locality.—Kern Valley, 25 miles above Kernville [= South Fork of Kern River 25 miles east of Kernville], Kern County, California (Merriam, 1893, p. 133).
Distribution area.—Roughly the western borderlands of the Mohave Desert, north into the Inyo region and south as far as the northwestern arm of the Colorado Desert. More in detail, the western side of Owens Valley including the adjacent east slopes of the Sierras north to the vicinity of Mammoth Pass; east from the southern end of Owens Lake through the Coso, Argus and north end of the Panamint Mountains; the extreme southern Sierras, including the entire drainage basin of the Kern River; the southern end of the San Joaquin Valley south of Tulare Lake, and the Carrizo Plains country and adjacent hills and valleys to the westward; the Tehachapi, Tejon, San Bernardino, San Jacinto and Santa Rosa Mountains and adjacent desert borders. The approximate line of blending between the races beecheyi and fisheri is shown on the map (fig. 17). With regard to life-zone the Fisher Ground Squirrel extends from the Lower Sonoran to the Canadian but its greatest numbers are reached, and most of its habitat lies, in the Upper Sonoran (see fig. 23).
Specimens examined.—A total of 96 specimens from the following localities, all in California: Inyo County: Little Onion Valley, 7,500 ft., east slope Sierra Nevada west of Independence, 1; Independence, 4; vicinity of Lone Pine, 3; vicinity of Jackass Spring, 6,200–6,500 ft., northern part of Panamint Mts., 9; Little Lake, 2; Olancha, 1; Little Cottonwood Creek, at 10,000 ft. alt., 1. Tulare County: Jordan Hot Springs, 6,700 ft., 1; Jackass Meadow, 7,750 ft., 1; Trout Creek, 6,000 ft., 3 Taylor Meadow, 7,000 ft., 5; Cannell Meadow, 7,000 ft., 1; Earlimart, 2; Tipton, 5. Kern County: Kern River, seven miles above Kernville, 1; Fay Creek, 4,100 ft., 2; west slope Walker Pass, 4,600 ft., 3; Weldon, 1; Isabella, 2; Bodfish, 1; Kern River, twelve miles below Bodfish, 1; eight miles northeast Bakersfield, 1; San Emigdio, 2; Fort Tejon, 5. San Luis Obispo County: near Simmler, on Carrizo Plains, 1. Ventura County: Mount Pinos, 3. San Bernardino County: Victorville, 2; Cushenbury Springs, 1; Doble, 7,000 ft., San Bernardino Mts., 1; Bluff Lake, 7,500 ft., San Bernardino Mts., 2; Fish Creek, 6,500 ft., San Bernardino Mts., 1. Riverside County: near Banning, 1; Cabezon, 9; Snow Creek, near Whitewater, 1; Schain's Ranch, 4,900 ft., San Jacinto Mts., 4; Fuller's Mill, 5,900 ft., San Jacinto Mts., 1; Round Valley, 9,000 ft., San Jacinto Mts., 1; Tahquitz Valley, 8,000 ft., San Jacinto Mts., 1; Strawberry Valley, 6,000 ft., San Jacinto Mts., 9.
The Fisher Ground Squirrel is closely related to, and in general very much like, the California Ground Squirrel with which it blends in Kern and Tulare Counties. In general appearance the former is slightly smaller and decidedly paler than the latter. The Fisher Squirrel may be recognized in the field by its extensive white shoulder patches. This sub-species is also known as "digger" squirrel.
The range of the Fisher Squirrel includes Kern Valley and part of Owens Valley, the extreme southern part of the San Joaquin Valley, and a strip of territory along the northern and western edges of the Mohave Desert from the mountains east of Owens Lake south to the Santa Rosa Mountains west of Salton Sea.
In altitude this squirrel ranges from 450 feet, as at Palm Springs at the eastern base of San Jacinto Peak, to 10,500 feet, as within a quarter of a mile of the summit of the same mountain (H. S. Swarth, MS). It is to be found from the southernmost plains of the San
Fig. 17. Map showing California distribution of the California, Fisher, Catalina Island and Douglas ground squirrels, and the Rock Squirrel, all being of the "digger" category. The spots represent localities from which actual specimens have been examined.
Joaquin Valley to 10,000 feet altitude in the Mount Whitney region. This rodent thus shows little regard for zonal limitations, occurring all the way from the Lower Sonoran zone to the Canadian zone, though its numbers above the Upper Sonoran are small. It is equally at home in the cultivated fields in the irrigated sections, about Bakersfield and on the rocky ridges of the Panamint Mountains.
At Jackass Springs, in the Panamint Mountains, Inyo County, on October 5, 1918, eight Fisher Ground Squirrels were counted in a three-hour census in the belt of sagebrush and piñon. These were invariably perched upright on the summits of gray granite boulders. They were even then notably pale-colored, with beecheyi in mind (J. Grinnell, MS).
At Mount Pinos, Ventura County, during the first week in July, 1904, Fisher Squirrels were present from the very summit (8,826 feet) down. They were trapped among the rockpiles near the top, and on the smooth slopes among the firs on the north side. Young were numerous, and quite unsuspicious, being run down with ease when caught a little ways from their retreats (J. Grinnell, MS).
Near Lone Pine in Owens Valley on June 16, 1917, Fisher Ground Squirrels were found inhabiting the lower embankment of the Los Angeles Aqueduct. At one point three miles south of Lone Pine, some thirty squirrels were noted along the aqueduct in a distance of half a mile. Other colonies were found along Lone Pine Creek at the edge of an old orchard (A. C. Shelton, MS).
In the region about Bakersfield Fisher Squirrels were found in considerable numbers near the mouth of Caliente Creek east of Bakersfield both in the wheat fields and on the adjoining plains covered with a low growth of cactus. In the irrigated region southwest of that city the squirrels were locally numerous on pasture land.
The Fisher Ground Squirrel as far as we can see is indistinguishable from the California Ground Squirrel in many particulars such as behavior, voice and mannerisms. This statement applies also to the general feeding and breeding habits of the form. Many incidents bearing on such points as enemies and natural checks have been recounted in our chapter relating to beecheyi, since they are for the most part identical in the two races.
Certain instances of behavior in the desert race seem worthy of special mention. At Isabella, Kern County, on July 4, 1911, W. P. Taylor (MS) states that it was a common thing to see the squirrels up from the ground in guatemotes or willows. At Palm Springs, Riverside County, on February 4, 1916, two Fisher Squirrels were seen to leap an irrigation ditch near town, a clear jump of about four feet (H. S. Swarth, MS). Sometimes individuals of this species do not hesitate to jump into water and swim, so as to escape from enemies. At Onyx, Kern County, on June 19, 1911, a half-grown squirrel was surprised on the bank of an irrigation ditch which was full of water. The stream was six feet wide, with rapid current. Without the least hesitation, the squirrel precipitated itself into the water and swam across, reaching the opposite shore by a diagonal down-stream course. It then quickly ran to a burrow, with the location of which it seemed familiar and from which it is likely to have come originally and crossed the ditch of its own accord for the purpose of foraging (J. Grinnell, MS).
The time of birth of the young in this species varies with altitude, more precisely zone, from April to late in June. At Cabezon, Riverside County, a one-third grown young one was secured May 16, 1908, while at 8,500 feet on Mount Pinos, Ventura County, a similar sized young one was taken July 11, 1904, At the former locality three juveniles and an adult female were drowned out of one community burrow in an almond orchard. This is probably about the minimum number in a litter, as the average number of young in a litter appears to be only slightly less than in the California Ground Squirrel. "The average number . . . of young at a birth . . . along the borders of the Mohave Desert appears to be . . . 6 or 7" (C. H. Merriam, 1910, p. 4). At Schain's Ranch, San Jacinto Mountains, on June 18, 1908, a family of eight young ground squirrels was observed aboveground at one time at the mouth of a burrow (W. P. Taylor, MS).
Regarding food preferences of this sub-species a special feature has been noted with extraordinary frequency, as follows. Many Fisher Ground Squirrels are taken in meat-baited steel traps set for predatory carnivores under circumstances which make it seem certain that they were caught while trying to steal the bait. They have also been known to eat woodrats and even other individuals of their own kind which they have found dead in traps.
At Kelso Pass, Kern County, on July 8, 1911, two Fisher Ground Squirrels came to drink at a seepage from a spring. One drank six times, the fifth time for over two minutes, by count of seconds (J. Grinnell, MS).
The following records of cheek-pouch contents establish some of the sorts of food taken by this animal. At Taylor Meadow, Tulare County, a squirrel was taken on July 25, 1911, with 88 seeds of a lupine (Lupinus grayi) in its cheek-pouches. Another squirrel taken seven miles above Kernville, Kern County, on June 26, 1911, was carrying a seed of the Digger Pine (Pinus sabiniana); while a third squirrel taken at Lone Pine, Inyo County, had gathered and placed in its cheek pouches 118 seeds of Encelia frutescens and 5 seeds of Hymenoclea salsola.
Squirrels of this subspecies were found doing a large amount of damage to the almond crop at Cabezon, Riverside County, on May 16, 1908. Here they were living right in the almond orchard, most of the inhabited burrows being dug close to the roots of the trees. Other short, shallow burrows were noted, but these were thought to be of use only for temporary protection in case the animals were taken by surprise (C. H. Richardson, MS).
In Antelope Valley, near Fairmont, Los Angeles County, on June 22, 1904, the authors found ground squirrels doing enormous damage to almonds, climbing the trees and biting open the green fruit to take out the pit and often leaving the hull in place on the tree. The pit was frequently found to have been removed from a remarkably small hole in the side or end of the shell.
At various points within the range of fisheri we have been told by old residents that digger squirrels have only recently invaded the locality and that a few years ago there were none where many squirrels are now present. In many such cases the sudden increase in the number of ground squirrels is evidently due not to invasion from without, but to the breeding up, under favorable conditions, of the local stock of squirrels which have been present all the time, but which was formerly so small and scattered that it did not attract attention. A typical example is as follows.
Residents of Owens Valley at Lone Pine stated in June, 1917, that the ground squirrels there had only recently invaded the valley and that none were known in that vicinity five years before. But from this same locality specimens now preserved in the Field Museum of Natural History in Chicago were obtained in 1902, fifteen years previously. Although the squirrels are said to be steadily increasing along the west side of Owens Valley, little or no effort appears to have been attempted at controlling the pest.
At the Carl Walters Ranch, two miles north of Independence, on June 26, 1917, Fisher Ground Squirrels were found to be fairly abundant on both this and most of the other ranches in the vicinity. They had been considered a nuisance here for a number of years (A. C. Shelton, MS).
The irrigation and cultivation of extensive areas have resulted in a greatly increased available food supply which has proven acceptable to the ground squirrel and has resulted in greatly increasing its population. It is the authors' belief that the squirrels have been present in Owens Valley from time immemorial and that as long as they were few in numbers and stuck to the rocky, uncultivated ground they remained largely unnoticed, but that when they invaded irrigated fields and became numerous they attracted attention and were then thought to have but just moved into the valley.
It is believed that, on the whole, there are only about half as many Fisher Ground Squirrels to the square mile throughout its range as there are California Ground Squirrels to the same unit of area in the range of that form. Fisher Squirrels nevertheless prove very destructive locally to cultivated crops. Many small isolated orchards and "dry-farmed" grain fields are scattered throughout the western and northern parts of the range of fisheri and these frontier ranches are the ones which suffer. While the money value of the crop destroyed may be small, yet such crops are often the settler's principal means of obtaining a livelihood and, although this may be humble indeed, its loss is felt critically. It is the authors' belief that the Fisher Ground Squirrel ranks third, or next after the Oregon Ground Squirrel, in point of economic importance in California.