Natural History of the Ground Squirrels of California/Douglas Ground Squirrel
Other names.—Douglas Spermophile; Digger Squirrel, part; Arctomys douglasii; Citellus douglasii; Citellus variegatus douglasii; Spermophilus grammurus douglasii; Spermophilus douglasii; Citellus beecheyi douglasii; Spermophilus grammurus beecheyi, part; Citellus grammurus douglasii.
Field characters.—As for the Beechey Ground Squirrel, from which differs noticeably in the possession of a blackish brown wedge-shaped patch on the fore part of the back; also shoulders more extensively silvery white, and tail longer. Length of body alone, in males about 11 inches, with tail about 8 inches more.
Description.—Adults in early summer pelage: Crown of head to nose buckthorn brown, becoming mixed with blackish toward eyes and ears; backs of ears deep bister brown margined behind broadly with clay color; insides of ears dull cinnamon-buff; eyelids white; whiskers black; side of head and of body behind shoulder deep bister brown, with much buffy white tippings to hairs; a conspicuous wedge-shaped patch on middle of fore part of back, with apex at nape of neck, solid deep bister brown in color, almost black in some specimens; shoulder patch extensively silvery white, this extending backwards to hinder end of median dark wedge. Hinder portion of body colored as in the Beechey Ground Squirrel, but dappling more conspicuous, due to the whiter tone of the light spots. Under surface of body of darker tone than in beecheyi, seemingly due to the darker, sepia brown, bases of the hairs showing through the dull white or buffy overwash. Feet as in beecheyi but clouded above with dusky. Tail colored as in beecheyi but light tippings to hairs greater in extent and whiter in tone, thus accentuating the white fringe, and producing a grayer effect throughout.
Color variations.—Young but a third grown usually show the characters of the species, both as to color and relative tail length, quite as well as do adults. In one example, however, the black dorsal wedge is considerably obscured by buffy mottlings, and it thus resembles beecheyi of the same age.
The effects of wear and fading rarely bring such extreme modification of color tones in douglasii as in beecheyi and fisheri, possibly due to the lesser intensity of the sunlight and dryness to which their habitat is usually subject. The black wedge on the fore back is most vivid in fresh pelage; in cases where wear and fading have progressed to an extreme degree, the black wedge is much dulled toward brown, and may be effaced almost entirely. The identity of the ground squirrels in any given locality can be determined with certainty by securing several individuals, when the normal, distinctive coloration is sure to be shown by some of them.
Measurements.—Average and extreme measurements, in millimeters, of seventeen full-grown specimens from the northwestern counties of California (Sonoma to Humboldt) are as follows: Twelve males: total length, 478 (438–504); tail vertebræ, 200 (175–221); hind foot, 60 (57–63); ear from crown, 23 (19–29); greatest length of skull, 60.5 (57.8–63.1); zygomatic breadth, 37.0 (34.9–38.2); interorbital width, 14.3 (13.5–15.7). Five females: total length, 439 (427–453); tail vertebræ, 192 (161–210); hind foot, 57 (56–60); ear from crown, 23 (18–26); greatest length of skull, 58.5 (56.8–60.4); zygomatic breadth, 35.9 (35.0–36.8); interorbital width, 14.0 (13.1–15.0).
Always taking age into account, there appear to be fairly diagnostic average skull characters for douglasii as compared with beecheyi, fisheri and nesioticus. Douglasii averages smaller in regard to auditory bullæ, and narrower as regards rostrum and braincase. Yet, as the above measurements show, the gross size of the skull is not especially different.
Type locality.—Probably somewhere in southern Oregon or northern California. The type was a hunter's skin "received from the banks of the Columbia" (Richardson, 1829, p. 172).
Distribution area in California.—Roughly, the northwestern section of the state, north of San Francisco Bay, west of the lower Sacramento River, and north of a diagonal line from near Chico northeast to the Nevada line near the southern 
OREGON GROUND SQUIRREL (AT LEFT). DOUGLAS GROUND SQUIRREL (AT RIGHT).
boundary of Modoc County. (See map, fig. 17.) Life-zone, Upper Sonoran and Transition, ranging down into Lower Sonoran along the western side of the Sacramento Valley. Altitudinally, the species ranges from near sea level up to as high as 6,500 feet (near South Yolla Bolly Mountain) and even 6,800 feet (on the Scott Mountains, Siskiyou County).
More in detail: The southern limit of the range of douglasii is not known to reach the Golden Gate; it falls, on the sea-coast, somewhere not far to the north of Point Reyes Station, and extends from there to the vicinity of Petaluma, leaving the southern two-thirds of Marin County uninhabited. It extends nearly or quite to Benicia and to the southern end of the range of hills west of Vacaville. The flood-plain of the Sacramento River forms the eastern boundary north to beyond the Marysville Buttes. Thence northeastward, across the Sacramento Valley, there is no obvious barrier. In Butte, Plumas and Lassen Counties the ranges of douglasii and beecheyi approach very closely, but so far as known they do not overlap; nor have undoubted hybrids or geographic intergrades been reported.
Specimens examined.—A total of 65, from the following localities in California: Modoc County: Sugar Hill, 3; Parker Creek, Warner Mts., 3; Deep Creek, Warner Mts., 1. Siskiyou County: Mayten, 1; six miles northwest of Callahan, Scott River Valley, 6; Summerville, 1; Castle Lake, 3. Shasta County: McCloud River, near Baird, 7. Tehama County: Mill Creek, 2 miles northeast of Tehama, 4; four miles south of South Yolla Bolly Mountain, 1. Butte County: four miles southeast of Chico, 4; Dry Creek, on Oroville-Chico road, 3. Glenn County: Winslow, 4. Yolo County: Rumsey, 1. Solano County: three miles west of Vacaville, 2. Humboldt County: Eureka, 1; Fair Oaks, 2; Ferndale, 1; Cuddeback, 1. Trinity County: Hayfork, 2; Helena, 2. Mendocino County: Sherwood, 3; three miles south of Covelo, 1; six miles north of Willets, 1; Mount Sanhedrin, 3. Sonoma County: seven miles west of Cazadero, 4.
The Douglas Ground Squirrel belongs to the group of large, bushy-tailed, tall-eared ground squirrels which include the California, Fisher, Catalina Island and Rock Squirrels, and in common with the first and second of these at least it is often called Digger Squirrel. Although the differences are not great, they are evident and should be recognized in economic work, for they not only concern color, but apparently also habitat and food preferences. The Douglas Squirrel differs from its next neighbor of the "digger" category, the California, in having a conspicuous blackish wedge-shaped patch on the middle of the back between the shoulders, in having the shoulder region more extensively grayish white, and in having the tail a little longer and grayer.
The name of the squirrel now under discussion was bestowed upon it (Richardson, 1829, p. 172) in acknowledgment to an early English explorer in western America, David Douglas, for having brought home specimens of the animals met with, many of which proved to be new to science. Douglas's travels carried him through parts of Oregon and probably northern California; but the type of this ground squirrel was a hunter's skin received from the Columbia River. There is no telling now exactly where it really came from originally, though probably from much south of the Columbia, since the species is not known to have existed within history that far north.
In northern California the Douglas Ground Squirrel occupies a wide area; in fact, at the extreme north from the Pacific Ocean to the Nevada line. To the southward its range includes all of the upper Sacramento Valley, and its western half lower down, and the whole coast region (hills and included valleys) south nearly to San Francisco Bay. Reference to the map (fig. 17) will show that the range of the Douglas is almost exactly complementary to that of the Beechey; at no point do they overlap, or, indeed, as far as known, quite meet. Roughly, the Douglas Ground Squirrel occupies the northern and northwestern third of the state.
The local or habitat preference of this species is more exclusively for hilly country than in the case of the California Ground Squirrel. It is true that the Douglas exists out on the floor of the Sacramento Valley nearly to the lands annually flooded along the river; but it occurs there interruptedly, in far separated "colonies," and never anywhere are the great numbers reached that characterize beecheyi in the San Joaquin Valley. The preferred haunts of douglasii are the openings or glades on hillsides, beneath scattered oaks or pines, or else the open tracts along stream courses, not, however, quite down to the water's edge. The edges of the smaller valleys between the coast ranges are well populated, but the open floors of these valleys are not often invaded very far or in any considerable numbers. Dense chaparral and thick woods are avoided altogether.
It is interesting to note here that where the coast redwoods have been lumbered out the Douglas Ground Squirrels have come in from the interior so as to be plentiful where formerly scarce or wanting. Chaparral slopes which have been swept by fire are also quickly invaded and occupied for a time, until the brush grows up thickly again. It is probable that the squirrels are unable to maintain themselves against enemies, such as bobcats, that habitually hunt by stealth through underbrush; the squirrels require a certain amount of space around them so that they can have a fair show of reaching the safety of their burrows after an enemy is first caught sight of. Even though the Douglas Ground Squirrels are nowhere so very numerous as compared with certain other rodents, their predilection for clearings brings them into economic prominence locally. We have been told repeatedly of cases where newly cleared farms in mountain valleys have been invaded at harvest time from the nearby hillsides, to the almost complete loss of the crops.
It is a curious thing that the Douglas Ground Squirrel should not occur south clear to the shores of San Francisco Bay, inasmuch as the Beechey on the south side of the bay extends up to either the very shore line itself or to the margin of the salt marshes adjacent, or did so until very recent years. This may be merely another indication of the lesser degree of aggressiveness or prolificness on the part of the Douglas Squirrel. Marin County seems to be devoid of any ground squirrels whatsoever, except for a few douglasii along the Sonoma County border. Joseph Mailliard (interviewed on May 8, 1918) states that in his forty years or more of residence in Marin County, he never saw any ground squirrels in the southern part or westwardly towards Point Reyes. Individuals were seen twice many years ago on the Rancho San Geronimo, but "they never stayed." To all appearances the conditions here are identical with those in the Russian River district and a few miles west of Petaluma where the animals in question are plentiful, or used to be until successfully combated.
Within the California portion of its range the Douglas Ground Squirrels are believed to be most numerous in Tehama County, this according to the consensus of opinion in the office of the State Superintendent of Rodent Control. In Shasta County, next on the north, there are relatively few. To the westward they extend within a mile of the seacoast in the vicinity of Eureka and at Cape Mendocino, but elsewhere mostly not closer to the sea than eight or ten miles. Nowhere in the immediate coast belt are they reported especially numerous or injurious. Pocket gophers there loom up as the most destructive rodent.
The voice and mannerisms of the Douglas Ground Squirrel are not to us in any points that can be remembered materially different from those of the California Ground Squirrel. A fair test of this could, of course, only be made upon the two if studied side by side under perfectly normal conditions. In the nature of the case this is impossible, for in no known locality do they occupy common ground.
The tail is at all times the most conspicuous feature of this ground squirrel. Sometimes when running to its burrow a squirrel will hold its tail in a continuously vertical position, or this member may be thrashed fore and aft. Ordinarily the tail is held nearly parallel to the ground, with more or less of an arch in it. In this posture of tail one is reminded strongly of the Gray Squirrel.
Our own observations, and the testimony of people in general who are familiar with several of our ground squirrels including the Douglas, indicate that the latter is the most prone of all to climb trees. For instance, near Tehama, June 8, 1912, several individuals were seen well up in large white oaks (W. P. Taylor, MS). At Winslow, Glenn County, June 19, 1912, one was seen in a buckeye, and several from twelve to fifteen feet above the ground in willows and cottonwoods (W. P. Taylor, MS). At Sisson, Siskiyou County, August 11, 1914, one was seen thirty feet above the ground in an incense cedar (T. I. Storer, MS). It is a common thing to see them perched upon the tops of fence posts or stumps. Individuals may under certain circumstances so nearly resemble Gray Squirrels as to be actually mistaken for them. This emphasis of the tree-climbing habit in the Douglas Ground Squirrel is, suggestively enough, thus associated with greater length of tail and grayer tone of color of tail, as compared with its nearest relatives. It seems, also, that this species, more generally than any other, raids orchard trees such as almond and apricot.
The sure test, on the basis of behavior, of a ground squirrel as compared with any true tree squirrel, such as the California Gray, is that the former, no matter how high in a tree when discovered, will, upon alarm, take to the ground as quickly as possible, and seek safety in a burrow below ground, rather than make off through the branches from tree to tree, or ascend into the uppermost foliage of a treetop. Not infrequently, when surprised in a tree, a ground squirrel will for the time being "freeze" and attempt to escape being seen by remaining motionless. But after being further disturbed and once starting, he makes for the ground by the shortest route.
The burrowing habits of the Douglas Squirrel are similar to those of related species. Steep banks seem to be chosen for burrowing into, whenever available. Many burrows open under rocks, bushes and tree roots. On open, level ground, with no protective shelter at hand, the mouths of the burrows are marked by good-sized mounds, showing the presence of an extensive system below ground. As far as we know, no one has yet made a complete excavation of the burrow system of this species.
The breeding season is indicated by the time of appearance of the young aboveground. In Scott Valley, Siskiyou County, where the species is abundant, very small young were seen abroad on June 8 (1911). At Winslow, Glenn County, young one-fourth to one-half grown were captured on June 16 (1912). At 6,800 feet altitude on the Saloon Creek Divide, in the Scott Mountains, Siskiyou County, July 10 (1911), nursing females were captured, but no young were yet out (L. Kellogg, MS). It is thus probable that at the lower altitudes the young are born during the last half of May, while at the highest levels they are not born until at least a month later. Only one litter is reared each year.
Unfortunately we have no facts of our own to offer in regard to size of litter. We have an idea that fewer young are born each year than in the case of the California Ground Squirrel, judging roughly from the numbers of young seen aboveground, about five. But this is almost pure conjecture. F. E. Garlough, of the United States Biological Survey, is under the impression (interviewed September 7, 1918) that litters in the lowlands average close to eight, while, in the mountains five is the usual number. He has known of as few as two and as many as fourteen embryos having been found in pregnant females.
The following definite data on file in the Museum of Vertebrate Zoology show some of the kinds of food selected by the Douglas Ground Squirrel and also the quantity in which each of these kinds may be gathered at one time. A male squirrel taken on Dry Creek where crossed by the Oroville-Chico road, in Butte County, May 31, 1912, contained in its cheek pouches 29 seeds of a wild lupine (Lupinus micranthus). Three others taken on Butte Creek, near Chico, June 3 and 5, 1912, contained in their cheek pouches materials as follows: male, 12 seeds of milk thistle (Silybum marianum); female, 219 grains of barley and one head of English plantain (Plantago lanceolata); female, 142 grains of barley. The cheek-pouch contents of two squirrels taken on Mill Creek, near Tehama, June 12, 1912, consisted of, respectively: female, 121 seeds of bur clover (Medicago hispida) and 70 small unidentified seeds, part loose and part in three whole pods; female, 181 seeds of brome-grass (Bromus carinatus) and one piece of an acorn. Two squirrels taken in the hills three miles west of Vacaville, July 3 and 6, 1912, contained in their cheek-pouches: female, 29 seeds of Napa thistle (Centaurea melitensis) and 30 seeds of bur clover; male, 82 seeds of bur clover, 4 seeds of Napa thistle and one cherry pit. A male taken three miles south of Covelo, Mendocino County, July 20, 1913, held in its cheek-pouches 14 whole fruits and 103 separate seeds of the common manzanita (Arctostaphylos manzanita), as also a few small unidentified seeds of two kinds.
From all sources comes the testimony that this species takes barley and wheat with particular avidity. Its storage propensities are highly developed, and it would be interesting to see actual figures as to the quantity of grain garnered underground in one autumn season. Where they invade apricot orchards, as in the foothill district of the Warner Mountains near Alturas, these squirrels climb the trees and take out the pits, discarding the pulp of the fruit.
The Douglas, as is known of most other ground squirrels, is fond of flesh when this can be obtained. Many have been taken in the meat-baited steel traps kept out in various localities for carnivores.
Hibernation seems to be more prevalent with douglasii than with beecheyi, for all of the population of the former is reported to disappear for weeks at a time, even in the lower valleys. At the higher altitudes, where there is more or less heavy snow, all the squirrels disappear over a period of some months. In Hayfork Valley, Trinity County, the senior author was assured by several different people living there that the Douglas Squirrels hibernate regularly and completely "from November till April." The earliest spring record we have for a mountainous region is of one squirrel caught in a box trap February 25 (1911) near Helena, Trinity County (A. M. Alexander, MS).
The natural enemies of this squirrel probably include practically all those already specified in our chapter on the California Ground Squirrel. Only one specific instance is at hand. A gopher snake found run over in a road near Chico, June 7, 1912, was found to contain in its stomach a young Douglas Ground Squirrel (T. I. Storer, MS). Coyotes are locally reputed to levy considerable toll upon this rodent. We have heard the argument advanced against the poisoning of ground squirrels on wild mountain land in the northwest coast district that reducing the squirrel population will deprive the coyote of one of his chief sources of subsistence and that he will thereupon be forced to seek food elsewhere and so be more prone to raid the poultry of the valley ranches and the flocks of sheep in the mountains. On the other hand, it may be advanced that the total coyote population is adjusted to the total amount of food available at the season of least supply, and that removal of any one important kind of food will in course of time reduce the total coyote population able to exist in any general territory.
A high natural mortality for this species may account for its relative lack of aggressiveness as compared with the California Ground Squirrel. The testimony of a number of people from localities widely scattered over the range of the Douglas Ground Squirrel is to the effect that every few years there is a great reduction in its numbers. Some fairly close observers, forest rangers in the Trinity region, for instance, think this is due to the effects of severe winter weather, as when there is an exceptionally heavy snowfall or torrential rains of unusual amount. In either case the squirrels are thought to be drowned in large proportion when lying dormant underground. Other persons think there are recurrent epidemics of some disease fatal to the ground squirrels. We have no good evidence bearing upon either hypothesis.
Because of this observed reduction in numbers during some winters, certain ranchers have objected to carrying on poisoning operations in the fall, since their efforts might prove to have been unnecessary. They prefer to. deal with the naturally reduced squirrel population of the springtime, at the close of the dormant period.
The general range of the Douglas Ground Squirrel has not changed within history as far as definite records show. But, locally, there have been marked fluctuations. On the western side of the Sacramento Valley the animals have been almost completely cleaned out on many large tracts as a result of systematic poisoning. This is particularly true, as we are assured by W. C. Jacobsen, State Superintendent of Rodent Control, of the Davis, Williams, Willows and Orland districts. The reason for this is twofold: The Douglas Squirrels never did have a secure foothold in the Sacramento Valley, such as the Beechey Squirrels have in the San Joaquin Valley; and the former, according to current impression, takes the poisoned grain more readily.
On the other hand, with the clearing of forest lands in the coast district, through lumbering and homesteading, the squirrels are thought to have extended their confines locally. At any rate, they have become numerous where formerly absent altogether or present in such small numbers as to have been overlooked by the average person.
In certain sequestered valleys among the northern coast ranges we have been assured of a loss to grain crops, where no effort at poisoning the squirrels had been made, of from 5 to 25 per cent. In such cases the squirrel population from the wild land immediately adjacent seemed to have moved in en masse, as harvest time approached, to take advantage of the special food supply thus made available. Nevertheless, the Douglas Ground Squirrel, by reason of its relatively sparse population over most of its range, and the ease with which it can be reduced in numbers with reasonable effort, does not rank as of so much economic importance as some other species. We would place it fourth among our ground squirrels, giving precedence to the California, Oregon and Fisher.