Animal Life in the Yosemite
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CALIFORNIA GROUND SQUIRREL. Citellus beecheyi beecheyi (Richardson)

Field characters.—Size medium for a squirrel (body length about 10 inches), tail long (about 7 inches) and haired at sides, but not so bushy as in tree squirrels; ear short, not tufted. Measurements: Head and body 9-1/8 to 10-3/4 inches (232-273 mm.), tail 6-1/3 to 7-7-2/3 inches (161-194 mm.), hind foot 2 to 2-3/8 inches (53-60 mm.), ear (from crown) 4/5 to 1 inch (21-27 mm.); weight 15-2/3 to 25-1/2 ounces (443-720 grams). General body color dull yellowish brown in effect; triangular area on each side of neck and shoulders, grizzled white; narrow area on fore part of back between whitish shoulder patches, dark brown. Voice: A sharp metallic alarm note or whistle, clink, usually uttered singly at varying intervals, but, when the squirrel is badly frightened, given two or more times in rapid succession. Workings: Burrows in ground, entrance holes about 4-1/2 inches in diameter; also runways, about 3 inches wide, through grass.

Occurrence.—Resident on west side of Sierra Nevada from plains of San Joaquin Valley up to middle altitudes in the mountains (highest record, 8200 feet, east of Merced Lake); observed on east slope of Sierras, at about 8000 feet altitude in Leevining Creek cañon, and locally in vicinity of Mono Lake Post Office. Most abundant on plains and in foothill country (Lower and Upper Sonoran zones), less numerous in the yellow pine belt (Transition Zone), and but sparingly represented in the Jeffrey pine belt (Canadian Zone). Frequents plains, small meadows, tree-covered hillsides, and rocky outcrops or granite taluses; commonest in open situations.

The California Ground Squirrel is probably known by sight to more residents of California than is any other one species of mammal, and it is also the one which most often excites the interest and attention of visitors from other states, because of its different appearance from that of prairie dogs and other squirrel-like animals of the more eastern parts of North America. It is to be seen in numbers from the windows of trains passing through the San Joaquin Valley, and is occasionally observed along the railroad in the Merced Cañon; while along all of the auto roads from the west leading into the Yosemite National Park it compels attention at almost every turn. Here individuals are prone to dash across the road almost under the wheels, uttering their startled cries and stirring up small clouds of dust to mark their precipitate rout. To the residents of the Sierran foothills this species is known as 'digger squirrel' in recognition of its propensity for burrowing and to distinguish it from the 'tree' squirrels, Gray and Red, which inhabit the middle and higher altitudes in the mountains.

Fig. 27. Cross-section of the Sierra Nevada through the Yosemite region showing general zonal and altitudinal distribution of Squirrels and Marmot.

The California Ground Squirrel is distinguished from the Gray and Red squirrels by the presence of whitish shoulder patches, by a less busby tail, and by ground-dwelling habits; from the Belding Ground Squirrel by larger size, and by much longer and broader tail, which undulates as the animal runs along the ground; from the Golden-mantled Ground Squirrel and the species of chipmunks, by larger size and by the absence of stripes of contrasted bright color along the sides of the body.

The California Ground Squirrel is most abundant on the plains of the San Joaquin Valley and in the adjacent foothills, in the Lower and Upper Sonoran zones; it is less numerous in the Transition Zone and but sparingly represented in the Canadian. The highest altitude at which we observed it was 8200 feet, a few miles east of Merced Lake. The California Ground Squirrel shares the Canadian Zone with the Golden-mantled Ground Squirrel, which fact may account in some degree for the lessened numbers of the former in that high zone. (See fig. 27.) Above, in the Hudsonian Zone, the meadowlands are inhabited exclusively by the Belding Ground Squirrel, while about rock slides and on the hillsides only the Golden-mantled is to be found. On the east slope of the mountains the California Ground Squirrel is present, but in very small numbers; a single individual was seen September 23, 1915, at 8000 feet altitude in Leevining Creek cañon, and a few were found in the vicinity of Mono Lake Post Office in May and July, 1916. On parts of the Great Basin plains beyond, its place is wholly taken by a small round-tailed species, the Stephens Ground Squirrel.

Over its entire range the California Ground Squirrel is resident throughout the year. Those individuals which live above the snow line in the mountains hibernate for considerable periods during the winter months. In Yosemite Valley, ground squirrels in 1920 were first seen out of their burrows about the middle of March, according to Mr. Forest S. Townsley. One exceptional individual was seen out by one of us, on the Big Oak Flat Road below Gentrys, on December 28, 1914. Those squirrels living at still lower levels, even though they may not go into regular hibernation, are still much less active in the winter season, when they are wont to appear above ground only during the mid-day hours of warm, sunny days.

As its common name indicates, this squirrel secures shelter for itself and young, and safety from its enemies, by burrowing in the ground. It seems to prefer to excavate its retreats in hillsides or in low earth banks, where most of the necessary digging can be done in a horizontal direction. But of course those members of the species which live on the plains or on flats or meadows in the foothills or mountains must perforce dig down vertically for considerable distances to gain the requisite protection. Most of the work of tunnel excavation is carried on during the spring months, as is shown by the mounds of fresh, soft earth accumulated at the mouths of the burrows in that season. In the lowlands, where there is a large crop of wild oats in the springtime, this newly excavated earth supports a ranker growth than do the surrounding parts of the field so that, as one of our party wrote in his field notes, "the plain looks like a cemetery overgrown with grass," with these taller stands of oats about the squirrel holes suggesting grave mounds. To some extent the ground squirrels, like the pocket gophers, thus serve as natural cultivators of the soil. Many of the squirrels which live in the granite country make their homes under large boulders or in rock taluses, where a minimum of burrowing is necessary to ensure safe retreats. This is notably the case in Yosemite Valley.

It is likely that the squirrels construct new burrows from time to time, or, what is even more probable, that each young individual as it comes to maturity and is weaned from its mother leaves the parent burrow and digs a home for itself. In any event, in places, there are many more burrows than individual squirrels present at one time. These tunnels, especially in the plains and foothill country, are joined together below-ground to a greater or less degree, as indicated by the fact that when hurriedly seeking safety squirrels will pitch down into any one of a number of holes in the vicinity of the one about which they were first seen, to reappear later somewhere else. Also, squirrel exterminators, when using gases or smoke in their work, find it necessary to stop up a number of holes adjacent to the one into which they introduce the fumes in order to force them into the lower reaches of the tunnels.

The burrows of the squirrels are often inhabited by species of animals other than the rightful owners. The so-called Burrowing Owls habitually make their homes in squirrel holes, probably deserted ones; and, to a less extent, the holes are frequented by California Toads, Western Gopher Snakes, and Pacific Rattlesnakes. It is likely that the presence of the latter two animals is not particularly congenial to the squirrels, as both of these snakes are known to eat ground squirrels when chance offers.

The burrowing activities of the California Ground Squirrel constitute a matter of considerable economic importance. The Yosemite Valley Railroad Company has found it necessary to reduce the numbers of the ground squirrels along its right of way through the lowlands; for the burrows of the animals weaken the grade embankments and, especially in wet weather, cause them to give way. The company has learned that the results obtained by their anti-squirrel campaigns fully justified the expenditure entailed.

Also, ranchers in the irrigated districts near Snelling patrol their ditches so as to discover and promptly plug up any and all squirrel burrows made in the banks, thereby preventing breaks, with consequent loss of the precious water.

Some years ago it was discovered that the ground squirrels in California were harboring fleas which carried the bacillus of bubonic plague. A vigorous campaign of extermination was waged against the animals and they were practically eliminated from many extensive areas. As soon as the efforts against the squirrels were relaxed, however, they began to 'spill in' from adjacent areas until now in most places they are as numerous as ever.

Ranchers living in the mountains find difficulty in keeping their meadowlands rid of squirrels. Mr. W. H. McCarthy, whose ranch is 3 miles east of Coulterville, told us that a regular patrol was necessary to keep his fields even approximately free. On the floor of Yosemite Valley attempts at poisoning ground squirrels have been made at various times during the past decade, but no appreciable diminution in their population was observable as a result of this work. In May, 1919, the squirrel population of the Valley appeared to be the largest of any of the years for which we have record.

Afield, the observer often comes upon ground squirrels which are some distance from their holes. Such animals usually run to the near vicinity of their burrows where they sit upright and can watch the intruder, yet be in readiness to dart down into their holes at an instant's warning. While thus on watch they utter, at short intervals, a rather musical whistled note, clink. If the farther advance of the observer seems to portend danger to them they utter a double note, clink, clink, sometimes with a sort of chuckle added, and then drop down into the shelter of their subterranean retreats. Ordinarily when thus frightened down, they do not reappear at the surface of the ground for some time, as if to give the suspected enemy plenty of chance to tire of his waiting and to depart: Occasionally, however, a squirrel will crouch motionless almost at the feet of the observer, as if to escape detection by remaining quiet. Extreme fear may be a part of the basis for this manner of behavior.

Ground squirrels, in traveling between their holes and their feeding grounds, frequently traverse the same courses until regular trails are worn through the grass. This is seen particularly well on the rolling lands between Merced and Snelling, where, in the fall, when the grass and weeds are dry, the trails show from a distance very distinctly. In the spring, when the new growth is just appearing, the trails are still conspicuous, as the vegetation is slower in starting there than in the adjacent unbeaten tracts. Soon, however, the trails are entirely obliterated, save as the animals renew them by further use.

It seems likely that ground squirrels can, if necessity demands, go without water for long periods of time, if not indefinitely. Many of the plains-dwelling individuals of this species are so situated that it is impossible for them to get any water except such as may accumulate in small surface depressions or in parts of their burrows for brief periods during the rainy season. As a substitute for bathing in water these animals take dust baths in the soft earth of fields and country roads. We have frequently come upon places where tracks and marks in the dust showed that squirrels had been 'dusting' themselves. This habit may afford partial relief from the many fleas and mites with which they are often afflicted.

Ground squirrels, like chipmunks, are provided with inner cheek pouches which are used while gathering and transporting food. Often when the animals are scared out of bushes or trees, or away from some supply of roots or bulbs which they have discovered, their cheeks are seen to be bulging with the contents of these pouches. They are able to use their teeth even when these pouches are widely distended.

Ground squirrels are chiefly terrestrial in their forage habits, taking whatever may offer in the way of seeds, grasses, fruits, low-growing annual plants, roots, and especially bulbs like those of the common brodiaea. The animals do leave the ground, however, and ascend shrubs and low trees for especially desirable provender. In Yosemite Valley, Mrs. Joseph Grinnell reports that ground squirrels were gathering the green fruits from the top of a 4-foot manzanita bush. At Pleasant Valley we occasionally saw them in low oaks, evidently after acorns; and at El Portal one squirrel was found with three of the large acorns of the Golden Oak, two in one cheek pouch and one in the other. At Snelling, in January, they were eating the coarse fruits of the osage orange, which abounds there as a hedgerow plant; torn remnants of these fruits were scattered about the entrances of the burrows. But the ground squirrel is not entirely restricted to a vegetable diet, as is shown by the fact that it is regularly captured in meat-baited traps set for skunks and other carnivorous animals.

Mr. E. W. Baker, formerly resident in Yosemite Valley, has told us that the ground squirrels about Yosemite Village would, in the fall, come and fill their cheek pouches with acorns and then go off and store them in some safe place for the winter or spring when food would be scarce. He says that the present species, like the gray squirrel, is not averse to stealing young birds. He has seen a California Ground Squirrel carry off a young Western Robin, and he has received report of their capturing young chickens in yards on the floor of the Valley. Numerous visitors to the Valley during the summer months establish feeding tables to attract the birds about their camps, and many of these persons find that ground squirrels give more or less trouble. At first exceedingly shy, the squirrels soon become bold and eventually have to be driven away in order that the birds may have the benefit of the proffered food.

In the lowlands the majority of the young ground squirrels are born in April and May, and by the middle of May some are beginning to appear with their mothers, playing about the mouths of the burrows; but in the higher altitudes the young are born later. Two half-grown young were seen on May 17, 1919, in Yosemite Valley, but in other years some of the females in the Transition Zone and lower part of the Canadian Zone had not yet given birth to their young by the first week in June. 'Spring' in the lowlands comes in April and early May, while the 'spring' of the higher altitudes does not occur until late June or July. Hence the young do appear at the same season, considering the differences in temperature conditions at the different elevations.

The annual molt takes place in mid-summer. With the advent of the new pelage, the white areas on the sides of the head and neck become more conspicuous and the pepper-and-salt effect resulting from the banded coloration of the individual hairs is more in evidence. As time goes on the freshness of the coat is lost by wear against the sides of the burrow and in other ways. The brown overwash which the new pelage possesses loses its reddish cast, and the hair becomes yellowish or grayish brown in appearance. There is thus some variation in the tones of coloration shown by squirrels of this species at different times of the year, irrespective of molt.


Animal Life in the Yosemite
©1924, University of California Press
Museum of Vertebrate Zoology

grinnell/mammals55.htm — 19-Jan-2006