Natural History of the Ground Squirrels of California/Oregon Ground Squirrel
Other names.—Oregon Spermophile; Bull Dog; Prairie Dog, part; Gopher; Bobby; Sand Rat; Short-tail; Woodchuck; Belding Ground Squirrel, part; Picket-pin, part; Spermophilus oregonus; Citellus beldingi, part; Spermophilus richardsoni.
Field characters.—A medium sized, short-tailed ground squirrel, of stocky build, and of brownish gray coloration without special stripes or markings of any sort (see fig. 20a). Length of body alone about 8½ inches, with tail about 2½ inches more.
Description.—Adult in slightly worn spring pelage: Whole upper surface of a general drab tone of coloration, tinged with cream-buff along sides and with dull cinnamon on top of head and down middle of back. There is usually a faint pattern of fine dappling. Eyelids dull white; whiskers black; ears clothed with short hairs, like top of head in color. Upper surfaces of feet tinged with warm buff; palms naked; soles naked except for sparse hairing forward from heel nearly to tubercles; claws horn-color, dusky at bases. Tail full-haired, flattish, widest about one-fourth way back from end; color on upper surface mostly like back, except for showing through of the hazel bases of the hairs, and for black zone about end succeeded by a buffy white fringe; under surface of tail bright cinnamon rufous, with a broad band of black at end and continuing backwards a little ways along either side, and the whole margined narrowly with buffy white. Under surface of body dull cream-buff, paling on throat and inner sides of legs; much brownish lead-color of the hair-bases shows through on abdomen.
Color variations.—As wear proceeds toward an extreme the whole coat becomes grayer, and the cream-buff tints tend to disappear by fading. Males usually remain much less worn than females; otherwise we can see no differences in coloration between the sexes. The material we have shows evidence of but one molt each year, this beginning about July 1st; but we have no specimens of dates between August and May. It is possible that there is an autumn molt leading into a distinct winter coat. Small young are softer-pelaged than adults, but colored just the same.
Measurements.—Average and extreme measurements, in millimeters, of nineteen mature specimens from northeastern California are as follows: Nine males: total length, 275 (260–300); tail vertebræ, 65 (56–80); hind foot, 42 (37–45); ear from crown, 9 (7–11); greatest length of skull, 45.1 (44.2–46.5); zygomatic breadth, 29.1 (27.1–31.0); interorbital width, 10.4 (10.0–11.1). Ten females: total length, 280 (271–292); tail vertebræ, 57 (47–68); hind foot, 43 (41–44); ear from crown, 7.5 (6–8); greatest length of skull, 45.7 (44.9–47.2); zygomatic breadth, 29.7 (29.1–30.4); interorbital width, 10.4 (9.7–10.9).
From the above figures it would seem that, in this ground squirrel, females are larger than males, except for tail and ear. There are chances, however, that measurement of greater numbers would give somewhat different results. It must be kept in mind that the figures taken from the freshly killed animals were supplied by several different people, and method of securing each measurement undoubtedly varies somewhat with the persons doing the measuring. Even with the skulls, all measured by the senior author of this paper, size clearly varies to some degree with age, and the proportions present in our series, of animals of different ages, will naturally affect the average.
Weights.—Average and extreme weights, in grams, of six full grown females are: 302 (267–365.8). This average in ounces is about 10½. The heaviest example was notably fat, the lightest, lean. Adipose tissue thus counts importantly in weight, though probably also weight increases, as does size of skull, with age. The animals would probably weigh most just prior to hibernation, as they are then fattest.
Type locality.—Swan Lake Valley, Klamath Basin [Klamath County], Oregon (Merriam, 1898, p. 69).
Distribution (in California).—Occupies the northeastern corner of the state, comprising the counties of Modoc, Lassen, eastern Siskiyou, and a portion of Plumas (see fig. 18). The metropolis of the species lies in the Upper Sonoran life-zone, but the animals extend through Transition, and even enter the Canadian. In detail: west from the Nevada line as far as the vicinity of Goose Nest Mountain, Siskiyou County, and vicinity of Big Meadows, in extreme northern Plumas County; south from the Oregon line to the last named locality and to the valley of Susan Creek, in Lassen County. Altitudinally, this ground squirrel extends from as low as 3,300 feet, on the Pit River, up to 9,000 feet, on Warren Peak, Warner Mountains (Mus. Vert. Zool.).
Specimens examined.—A total of 51 from the following localities in California: Modoc County: Sugar Hill, 4; Goose Lake near Davis Creek, 2; South Fork Pit River near Alturas, 3; Warner Mts. (Parker Creek and Squaw Peak), 6. Siskiyou County: near head of Little Shasta River, north of Goose Nest Mt., 1; Bull Meadow, northeast of Goose Nest Mt., 1; seven miles south of Macdoel, 24; Grass Lake, 6. Lassen County: Termo, 1; west end of Horse Lake, 1; fifteen miles west of Westwood, 1. Plumas County: ten miles west of Big Meadows, 1.
The Oregon Ground Squirrel occurs in California only in the extreme northeastern counties of the state; but it has a rather wide general range which includes much of Oregon east of the Cascades, and parts of northern Nevada. It is a Great Basin plateau species, and its range ends to the westward in California rather abruptly in the vicinity of Goose Nest Mountain (head of Little Shasta River and Grass Lake) and in the Pit River Valley in the vicinity of Burney, Shasta County. To the southward it extends to Big Meadows, in Plumas County a little southeast of Mount Lassen, and to the valley of Susan River, in Lassen County.
Fig. 18. Map showing California distribution of the Oregon, Belding, Stephens Soft-haired, Mohave, Yuma Round-tailed, Death Valley Round-tailed and Palm Springs Round-tailed ground squirrels. The spots represent localities from which actual specimens have been examined.
Beechey Ground Squirrel individually, it exceeds that species in numbers. At any rate, it ranks highest in importance among rodent pests within its domain.
The Oregon Ground Squirrel is an inhabitant chiefly of mountain meadows and the borders of the bigger meadows of the valleys. It does not care for marshy ground, and it avoids thick brush and rocky slopes. In a way, it is complementary in habitat to the Douglas Ground Squirrel, which occurs in much of the same territory; rarely are the two seen on common ground. It is obviously because of its preference for grass land that the Oregon Ground Squirrel has come so seriously into conflict with man's interests. Extensive clearing of the sagebrush and seeding of these clearings to grain and hay has doubtless benefited the squirrels. Indeed, this is likely one of the factors that accounts for their increase of late years as testified to by several of the old-time residents whom we have interviewed.
In Butte Valley, Siskiyou County, the Oregon Ground Squirrels are popularly known as "bull dogs," in Modoc County as "short-tails" (evidently as distinguished from the longer tailed Douglas Ground Squirrel), and elsewhere, locally, as "bobbies," "prairie dogs," "gophers," and "woodchucks." The last three names, of course, are misapplications of names properly belonging to quite different kinds of rodents.
In the latter part of May, 1918, the senior author accompanied Mr. W. C. Jacobsen, State Superintendent of Rodent Control, in a tour through northeastern California for the particular purpose of studying the Oregon Ground Squirrel. In traveling eastward from Shasta Valley, we first encountered this species toward the head of the Little Shasta River, on the Mills ranch at about 4,200 feet altitude. Here we found a field of vetch to be riddled with the burrows and secured one of the animals to verify this, the westernmost record station for the species. At Bull Meadows, a little east of Goose Nest Mountain, the squirrels were exceedingly numerous on the uncultivated open ground among scattering lodgepole pines. Subsequently we found them plentiful around the margins of Grass Lake, nearly as far west, but due south of Goose Nest. But it was on the floor of Butte Valley, from the vicinity of Bray north to Dorris, wherever there were open grass lands, that the Oregon Ground Squirrels simply swarmed. The following observations made May 16, 1918, on a ranch seven miles south of Macdoel, will give an idea of the abundance of the animals where conditions are most favorable to them.
Taking a position at the right-angled intersection of two fences, the observer counted the animals in the quarter-circle gaze thus bounded and found that there were sixty-five squirrels in plain sight within a distance of one hundred yards of him. This was about nine o'clock in the forenoon of a bright day, when the squirrels were at about the height of their daily activity aboveground. Young of the year were included.
Again, three adjacent plots of pasture were paced off, thirty-nine paces square, and the open burrows counted. In one plot there were 151, in the second 182, in the third 194, an average of 176. This, figured out, makes 560 open burrows to the acre! If we allot one adult squirrel to each five openings, which our observations showed to be about the proper ratio, there would be 112 adults to the acre, not counting young. Figuring, further, this would make somewhat over 70,000 squirrels per square mile! This, however, would pertain only in limited areas and to those pasture lands where little effort had yet been made to reduce the pests. The population of the sagebrush plains and pine woods of Butte Valley would be much smaller. It is, of course, the pasture lands and grainfields where the squirrels come into chief conflict with man's interests, and this is where they are most abundant. Some further estimates in this connection are likely to prove worth while.
The average weight of six adult female Oregon Ground Squirrels was found to be 302 grams (about 10½ ounces). The full stomachs of these six squirrels were found to give an average weight of 18.5 grams. Subtracting the ascertained weight of the stomach itself (3.5 grams), gives the weight of the contents, alone, representing doubtless one full meal, as 15 grams, or one-twentieth the entire weight of the animal. The stomach contents was in all cases a closely packed, slightly moist (not watery) mass of finely chewed green stuff. This could not be analyzed as to kinds of plants represented, but the squirrels were seen to be feeding upon all sorts of vegetation, practically everything going to make up the usual forage grazed from such lands by live stock.
Our observations led us to believe that, at the very least, two full stomach-loads of greens were eaten by each squirrel each day, or 30 grams of forage. Of course this does not account for wastage, evidence of which, in the way of cut stems and grass blades, was plentiful. Figuring from the average number of adult squirrels per square mile, 70,000, and counting on two meals per day, we find a minimum of 2,100,000 grams, or somewhat more than two tons, of green forage devoured by the squirrels each day on a square mile of pasture. Granted that a grazing steer eats fifty pounds of pasture forage each day, we conclude that the squirrels on a square mile of pasture appropriate each day the forage which might support ninety head of cattle.
Expressing it in other ways, 750 Oregon Ground Squirrels during the growing season of pasture grass eat as much as one steer, and the squirrels on every seven acres of pasture thickly inhabited by them eat as much as one steer!
The burrows of the Oregon Ground Squirrel where the animals are at all numerous fairly riddle the ground. Most of the openings come to the surface at a rather steep angle and without any earth at their mouths. Now and then there is an opening which slants to the surface and has a good-sized mound, and such as these seem to mark the nesting burrows as distinguished from the short, temporary, refuge burrows, or those occupied by males. We spent the entire day of May 16 excavating one nesting burrow, with results shown in figure 19.
The mound at the main entrance to this burrow system was rather large in extent, though shallow. It consisted of this year's loosely piled earth, covering up the grass on an area of nearly two square yards and thus marking the place conspicuously. The system of burrows, in part at least, probably represented two seasons' work and maybe more. While there were only two openings to this system, there were several points at which underground branches came nearly to the surface so that a hard-pressed squirrel, pursued by some underground enemy, could have quickly dug clear out and escaped overland.
As usual with ground squirrels, the runways were everywhere smooth and free from excrement, the nest chamber in use being unexpectedly clean. The feces of the young are evidently collected by the mother and carried to the places where her own are deposited, in the special branches or defecatoria. Here the earth is tamped over the mass in such a way that the pellets are kept separated by the soil particles, with no chance to fester. The fecal pellets are dryish, anyway. Some saved for examination, probably from the adult squirrel, prove to be 
Fig. 19. Plot of a used nesting burrow of the Oregon Ground Squirrel, as excavated by J. Grinnell and W. C. Jacobsen in a pasture near Macdoel, in Butte Valley, Siskiyou County, May 16, 1918.
Main opening of burrow-system at a, with shallow, bean-shaped mound nearly two square yards in extent opposite. Greatest depth of earth in mound, 100 millimeters. Only other opening, at s, flush with surface, and without any out-pushed earth. Mouth of burrow at a, 100 millimeters wide by 90 high. Mouth of opening at s, 75 by 60. Dimensions of burrow at f, 75 by 60 mm.; at c, 90 by 65; at d, 60 by 60; at o, 60 by 60.
Depth of burrow at b, beneath surface of ground, 300 mm.; at c, 350; at d, 200; at f, 300; at g, 520; at h, 590; at j, 750; at k, 1,000; at o, 660; at p, 520; at r, 550. Branches at i, e and t came nearly to surface of ground. Old nest cavity at k, 300 mm. in diameter, and floored with a damp mixed mass of old frazzled grasses, excrement, and earth. At m and l, chambers, 770 and 1,110 mm., respectively, beneath surface of ground, packed full of a mixture of excremental pellets and loose earth. Blind terminal at n, 850 mm. deep. New nest, in use, containing many live fleas, at g; cavity of this, 190 mm. wide by 170 high, and 700 mm. beneath surface of ground, nearly filled with a dry clean hollow mass of shredded juniper bark and weathered grasses. The excavating was begun at a, and the female and six third-grown young were overtaken at s and t, where they were about to escape.
Total length of this burrow system, 66 feet. Average diameter of burrow, 2½ inches. Volumetric content of entire system, 3½ cubic feet. Greatest depth reached, 45 inches, or nearly 4 feet.
short-cylindrical or elliptical in shape, and measure 6.5 millimeters in diameter by from 15 to 22 in length.
There were two nest cavities in the system unearthed, an old one, and the one in use. The latter contained a dry, hollow mass of frazzled juniper bark and weathered stems and blades of grass. The female parent and six third-grown young were overtaken farther along in the burrow system, near one terminus of it, but that the nest had but recently been vacated was shown by its feeling of warmth to the touch and the presence of numerous lively fleas. The female proved a tartar in defense of herself and young, biting effectively with her sharp incisor teeth and scratching with her strong claws. This was as a final recourse, however, as the first endeavor on the part of all the occupants, when the burrow was opened up, was to escape and run to the nearest shelter, such as offered by some neighboring burrow, or by a flat rock. As far as our observations went, there was no indication that the adult male lives in the same burrow with the female, or has, indeed, anything to do with the rearing of the young.
The burrow system in question was found to be 66 feet long, including the various windings and all of its branches. Its average diameter was about 2½ inches, and the volume, or cubical air content, 3½ cubic feet. The greatest depth reached beneath the surface of the ground was 45 inches. This was in rather dry pasture, and there was no sign of a water-table; the soil to this depth was only moderately damp.
The notes of the Oregon Ground Squirrel are of two sorts. The most impressive consists of a series of from 8 to 12 shrill, high-pitched calls, uttered in rapid succession—seep, seep, seep, seep, seep, seep, seep, seep, seep. The tendency is to weaken on the last few syllables, but the same pitch is nearly or quite maintained throughout. This call seems to be uttered only by adults, and seems to signify alarm at the first, or distant, approach of danger. One hears it taken up here and there all over a large meadow when it is first entered. Then there is a single shrill chirp of somewhat lower pitch, uttered now and then by either old or young. At times one will hear scarcely a note for many minutes, even when many of the squirrels are in sight, and then again the calls will be given back and forth from all sides.
One old female watched from a distance of 20 feet stood stock still for several minutes at the mouth of her burrow, in upright, "picket-pin" fashion. The fore feet she held against her stomach in front. When she gave the several syllabled call she opened her mouth very wide, depressing the tongue on to the floor of her mouth so that it could not be seen, and uttered the successive notes with much appearance of effort. The convulsive movements of the body were synchronous with the notes as uttered. The picket-pin attitude is really not so frequent as a crouching one, though when it is assumed it renders the squirrel visible a long way, especially where the grass is short. When feeding, the squirrel hunches over on its haunches, and uses both front feet and the fingers of these for holding and manipulating the food. When foraging the squirrels do much slinking along, with body horizontal and seemingly touching the ground. When a general alarm is sounded one sees them running in every direction, with a rather clumsy and not rapid, hopping gait. When so running the tail, short and never conspicuous, is held either out straight behind or raised at an angle of 30 degrees. Often when halting, or coming to a stand on the alert, the tail is twitched up from the horizontal several times in rapid succession, the whole body also twitching at the same time.
Rarely does an Oregon Ground Squirrel leave the ground, even to climb onto a rock or log. The body is relatively heavy and the general movements are far from nimble. In just one instance was a squirrel observed to have actually climbed; one individual was seen at Sugar Hill, Modoc County, up in a bush four feet above the ground (W. P. Taylor, MS). Marshes or very wet meadows are avoided; in other words, this species does not take to water. Still, we have the one instance of an individual, near Canby, Modoc County, seen (W. C. Jacobsen, MS) swimming across the Pit River. The current here was sluggish and the channel about eighteen feet wide. The act was to all appearances voluntary.
At the season of our special observations, the middle of May, the Oregon Ground Squirrels were seen to be feeding on practically every sort of pasture vegetation. Cuttings of meadow grass, blades and stems of grain, and leaves and stems of alfalfa were seen on their mounds or in the mouths of their burrows. As already stated, determination of the kinds of plants eaten, from stomach examination, proved impracticable because the food is chewed so finely. Even young less than a third grown were feeding freely on green stuff. Six young taken on May 16 were found to weigh from 65.1 to 104.7 grams, averaging 82.4 grams as compared with 302 grams, the average weight of adults. Their stomachs were distended with finely cut food, and were found to weigh on an average 5.4 grams, or about one-fifteenth their total weight as against the one-to-twenty ratio in adults. It would seem that partly grown young eat more in proportion to their size than old squirrels—which was rather to be expected.
There seem to be two periods of maximum daily activity aboveground on clear days, about 9 a.m. and again in mid-afternoon. This squirrel seems to be preeminently a sunshine forager. One day when a thunderstorm came up in the afternoon the squirrels nearly all disappeared from aboveground coincidently with the gathering of the clouds.
The breeding season of the Oregon Ground Squirrel, as is to be expected, varies with altitude, or, rather, with life-zone. The young are born later in the Transition and Boreal zones, than in the Upper Sonoran. On May 15 scores of adults were seen on Bull Meadows, near Goose Nest Mountain, 5,000 feet altitude, in the Canadian zone, but not one youngster was seen; while on May 16 everywhere in Butte Valley around Macdoel, at 3,000 feet, in the Upper Sonoran zone, young were out in great numbers. All of these were of about the same size, one-fourth to one-third grown, showing the uniformity of time of birth throughout a region of uniform temperature conditions. On May 19, 1910, a collecting party from the California Museum of Vertebrate Zoology found small young, just out, on Sugar Hill, 5,000 feet altitude, Modoc County.
There is but one litter a year, and the number to a litter is supposed to vary from 4 to 15, averaging about 8. Exact statistics from which to determine these figures accurately are not available. A man who was irrigating an alfalfa field near Macdoel regularly day after day told us that he had drowned out many families of young and that the broods he had seen consisted of from 4 to 11, averaging, he thought, 8. Mr. W. C. Jacobsen, from his own extensive experience with this species, considers 4 and 12 to be extremes, and 8 the average. He knows, indirectly, of one case of 15.
The Oregon Ground Squirrels lie dormant in a dry nest beneath the surface of the ground for fully half the year, even at the lowest altitudes in the general territory inhabited by them. The bulk of the population goes into hibernation during July and does not come out until March. These statements are made upon the authority of Mr. W. C. Jacobsen, who is further of the opinion that the exact time of disappearance, which varies somewhat from year to year, is controlled by moisture and consequent supply of green food. The drier the year the earlier the squirrels go into winter quarters, this in spite of the hotter late-summer temperature at the lower altitudes. In 1915, the squirrels in Big Valley, Lassen County, had nearly all gone in by July 3; in Warm Springs Valley, Modoc County, they had gone in by July 10; but on the Warner Mountains, Modoc County, they were just going in on July 22 of the same year. In 1914, a year of more moisture and better feed, the time of 
SIERRA GOLDEN-MANTLED GROUND SQUIRREL (AT LEFT). BELDING GROUND SQUIRREL (AT RIGHT).
beginning hibernation at the same points was one and one-half to two weeks later. Individuals have been reported to us as seen aboveground as late as the first week of September, but all reports agree that the majority are "holed up" before the first week in August.
In the spring the animals reappear often when there is yet much snow on the ground. In 1916 they were out in force on March 16, when they had burrowed up in places through two feet of snow and were nibbling the sagebrush tips (W. C. Jacobsen, MS).
Enemies of the Oregon Ground Squirrel were, under original conditions, doubtless numerous and effective in keeping down its numbers. Gopher snakes, rattlesnakes, badgers, coyotes and Swainson Hawks are known to feed regularly on it. Mr. J. O. Miller, a professional trapper living at Yreka, informs us that nine out of ten coyotes trapped by him during the summer months have remains of ground squirrels in their stomachs. One coyote taken in Butte Valley had parts of seven Oregon Ground Squirrels in its stomach. An old-time resident near Alturas told the senior author that the killing off of the "varmints" (predaceous animals) in recent years seemed to him to have had something to do with the increase and spread of ground squirrels. We are strongly inclined to his belief. Encouragement of those natural enemies which are not in themselves seriously detrimental to man's interests would go far to check the undue increase of the ground squirrels.