CALIFORNIA GRAY SQUIRREL. Sciurus griseus griseus Ord

Field characters.—A typical squirrel, of large size; general form slender; tail a conspicuous 'brush.' about equaling body in length, broad and flat. (See pls. 33b, 34.) Head and body 10 to 11-5/8 inches (256-296 mm.), tail (excluding hairs at end) 9-1/2 to 11 inches (240-280 mm.), hind foot about 3 inches (72-80 mm.), ear (from crown) 1-1/8 to 1-1/2 inches (28-36 mm.); weight 26 to 32 ounces (733-913 grams). Coloration above uniform gray, with light steel gray pepper and salt effect at close range; under surface of body pure white; tail gray margined with white. Voice: A hoarse, asthmatic coughing note, uttered usually in slow series. Workings: Kitchen middens, consisting of remains of pine cones dissected to obtain seeds; nests of large size among branches of coniferous trees, or else in cavities in oaks.

Occurrence.—Resident in Upper Sonoran and Transition zones on west slope of Sierra Nevada. Recorded from Pleasant Valley eastward to Aspen Valley, Yosemite Valley, and Chinquapin. Inhabits large trees and ground close by. Diurnal. Solitary.

California Gray Squirrels are present in small numbers throughout the digger pine belt of the western foothills (Upper Sonoran Zone). The relatively small number of trees there and the consequent limited supply of nuts (upon which these animals largely subsist) is probably at the base of this sparseness of the squirrel population in that belt of territory. Immediately upon passing into the main forest belt of the mountains (Transition Zone), characterized by the presence of the yellow pine, the observer marks an increase in the numbers of these squirrels, doubtless correlated with the denser stand of trees and much larger crop of various nuts. At the upper margin of the Transition Zone the range of the Gray Squirrel meets that of the Red Squirrel or Chickaree, a species of similar food habits; and the ensuing competition seems to be one of the factors operative in limiting the upward extension of the Gray Squirrel's range. (See fig. 27.)

The California Gray Squirrel population in the tree-clothed parts of the foothills is perhaps not more than one animal to every 10 acres; in the yellow pine belt there is perhaps one to every 3 or 4 acres. On the floor of Yosemite Valley, in certain years at least, the density of population reaches one an acre. In October of 1914 the numbers were at their maximum; more than 4000 were computed to be on the Valley floor and the lower slopes adjacent. But the squirrel population is subject to fluctuations from time to time and place to place. In the spring of 1916 the number of these animals on the floor of Yosemite Valley was very much less than in the fall of 1914.

The California Gray Squirrel is the largest of the local squirrels (save the marmot), being somewhat heavier than the California Ground Squirrel and very much bigger than any of the other species. The Gray Squirrel shows specialization for life in trees in several obvious ways. Its body and legs are long and slender and very strongly muscled so that it can leap considerable distances between branches. The toes are all provided with sharp curved claws which serve well in enabling the animal to cling to the irregularities of the bark of trees and to sprays of foliage. The tail is long and broadly haired to serve as rudder and counterbalance in the various movements of the animal. (See pls. 33b, 34.)

On the ground a Gray Squirrel moves by a series of jumps. The front and hind legs act in pairs, the front ones being held close together while the hind ones spread out widely and are carried forward beyond the body. When traveling at full speed one of these squirrels has been found to have covered as much as 4 feet in a single bound over snow. When ascending a tree its movement is similar; the squirrel 'gallops' up the trunk, often with all four feet off the bark at the same instant. The fine curved claws on the toes of each foot catch readily in the bark and hence the squirrel often has an even firmer hold when in a tree than when on the ground. In descending a tree, which the squirrel does head first, the hind feet are turned outward so that the claws of the hind toes will catch on the bark; and the feet are moved alternately.

Where trees are so close that the branches overlap or nearly touch, a Gray Squirrel may travel aloft for long distances without once coming to the ground; if occasion demands, the animal can run through the tree tops at a relatively high rate of speed.

California Gray Squirrels are active throughout the year, showing no tendency to hibernate as do the ground squirrels. On stormy days they usually remain in their nests, but they promptly fare forth as soon as the weather clears. Their ability to be abroad during the winter is probably due to the fact that their food, consisting of fruits, nuts, and fungi, is practically all aboveground, and that it persists nearly or quite through the winter. Moreover, when this food is most plentiful, in the autumn, the squirrels lay by a reserve, to be drawn upon later as needed. The greatest activity on the part of the Gray Squirrels comes in the fall months, when the season for acorns and pine cones is at its height, and when the squirrels embrace the opportunity to gather in reserve supplies. These nuts they store for the most part by burial in the ground, a nut here and a nut there over a considerable area in the vicinity of their headquarters.

The only note which the California Gray Squirrel has been heard to utter is a coarse, harsh 'cough' or bark which to the ears of most persons is anything but pleasant. While sometimes uttered singly, the notes are usually given in series of 4 to 6 at relatively short intervals; when a squirrel is excited several series of notes may be run together so as to be practically continuous. The Gray Squirrel's vocabulary is thus much less varied than that of the Red Squirrel. Twice, when members of our party were watching Gray Squirrels up in trees, the animals were seen to beat rapidly with one front foot (the left, in one of the cases, the right in the other) on the limbs on which they were resting. The noise in one case sounded like that made by a woodpecker. The squirrel seemed surprised or concerned at the observer's presence and this may have stimulated the pattering. Other mammals, for example wood rats and rabbits, are known to stamp with their feet when excited.

Gray Squirrels build nests as shelters in which to rear their young and as places in which the adults can find refuge during inclement weather and at night. Instead of choosing one type of location, two very different sorts of places are selected, and separate kinds of nests accordingly constructed. When natural cavities, resulting from the rotting out of good-sized branches, are available in oak trees, the squirrels line these cavities with soft material and use them. Failing to find some appropriate shelter the animals build regular nests, out in the open branch-work of trees, somewhat after the manner of many birds. The case is roughly paralleled by that of the Streator Wood Rat, which either builds stick 'houses' on the ground or in trees, or else occupies the interior of fallen logs or crevices in rocks.

Two 'outside' nests of the Gray Squirrel were found in separate but adjacent yellow pines of medium size on the divide between Bean and Smith creeks, east of Coulterville, on June 6, 1915. The two were so nearly alike as to location and details of construction that description of one will suffice. The height of the nest above the ground was about 60 feet; it was placed against the trunk of the tree (which at that height was about 3 inches in diameter) and it was supported by a whorl of branches. The outer, coarse framework of the nest was of yellow pine twigs 1/4 to 1/2 inch in diameter and 6 to 18 inches in length; on many of these the dried terminal tassel of needles was still adhering. Within this broom-like envelope was a packed mass of softer material consisting of yellow pine needles, shredded bark of incense cedar, and grass stems, all dried. Here also were acorn hulls and shells of manzanita berries, suggesting that the occupant had eaten food while in the nest. There were also a few pebbles in this layer, but the reason for their presence was not evident. The inner-most element, or nest proper, at the top of the structure, was of bark and grasses, finely shredded and consequently of very soft texture. The main bulk of the structure, below the nest cavity, was very damp, probably as a result of rains a couple of weeks previously. The outside dimensions of the whole structure were: average diameter 17-1/2 inches, height 11 inches. The soft-lined cavity at the top was about 6 inches across and 3 inches deep at the center. After being removed from the tree the whole structure was found to weigh 10 pounds. There was no canopy or covering to this particular nest, though as a rule outside nests are roofed over.

Other nests of California Gray Squirrels were 'spotted,' by members of our field party seeing the squirrels go to them. One outside nest, in Yosemite Valley, was about 75 feet above the ground in a lodgepole pine. At Smith Creek a nest was found in a black oak, in a cavity formed by the rotting out of a large branch 35 feet above the ground. The soft nest in which the young had been reared was 2 feet below the entrance hole. In Yosemite Valley several squirrels were seen to disappear into cavities high up in black oaks. On three occasions in early September, Gray Squirrels were seen carrying to such nests loads of lining material. One animal in particular, seen scampering along a road, had long wisps of grass sticking out on both sides of its mouth. The squirrel ran up a black oak and disappeared with the material into a hole near the top of the tree. Another, in Yosemite Valley on December 24, 1914, was carrying in a great roll of needles of the yellow pine.

The two principal items in the diet of the California Gray Squirrel are the seeds of pines and the acorns of oaks. These, together, are available over a long season; and the squirrel tides over the balance of the year by gathering and hiding away a surplus. 'Bracket fungi' growing on the trunks of trees are eaten at times. There is a strong suspicion, supported by much circumstantial evidence but by little direct observation, that Gray Squirrels rob birds' nests in season. A change to a diet of fresh meat may be sometimes welcome.

The seeds of the yellow pine and sugar pine are eagerly sought by all the Gray Squirrels living within the territory occupied by these trees. In the foothill country the seeds of the digger pine are gathered. With the advent of the first new seed-bearing cones in midsummer the squirrels turn their attention to the pine trees and continue to use the cones until the last of them are gone, in late winter.

When in search of food, a squirrel will run about the branches of a tree until it finds a suitable cone and then with a few quick strokes of the sharp incisor teeth will cut through the stem of the cone. Light cones are usually seized, carried to some convenient place in the tree, and there opened up, but a heavy cone is let fall to the ground. Often several cones are cut off in quick succession, then the squirrel descends, to attend further to its harvest. If the cones are not too heavy the squirrel seizes one in its mouth and repairs to some log or lower branch in the tree. But if too heavy to carry, as in the case of the cone of a sugar pine, the cone is opened right on the ground where it fell, or it may be dragged a little ways, up close to the base of the tree. The procedure in opening the cone to obtain the seeds is practically always the same; most cones are held in the forepaws, but very heavy ones are turned over and over on the ground.

A pine cone consists of a central core upon which the flattened scales are disposed in spiral series. Beneath each scale, in the case of the pines and firs, lie two seeds. The squirrel, to obtain the seeds in the green cone, begins at the upper (stem) end and systematically cuts off the scales at their points of attachment to the core. To do this the cone is rotated so as to bring fresh uncut scales before the animal's chisel-like teeth. At the upper end of the cone, seeds are small or wanting; but as soon as this region is passed, the removal of each scale uncovers two large seeds. These, in the green cone, already have the covering which later becomes the shell of the pine nut, and also the flat wing; but the seed coat is still soft and a stroke or two of the teeth exposes the green yet tasty meat which is, of course, the objective of all the squirrel's efforts. This process of cutting off scales and disposing of the seeds is continued until nothing remains but the stripped core and a pile of scales and shells of seeds. All through the summer, autumn, and winter months these fresh kitchen middens are to be seen on the ground at the bases of large trees, or on logs or boulders, showing where the squirrels have been feasting.

Acorns from the black, golden, or live oaks are either picked in the trees, one at a time, or else gathered up after they have ripened and fallen to the ground. If to be consumed on the spot only a few strokes of the teeth are needed to shell out the meat or 'mast.' But many of the acorns are buried entire in the ground, single nuts being placed in little pits dug here and there, and then carefully covered up. There is no doubt whatsoever that this habit of the Gray Squirrels is a beneficent one with respect to reforestation, in that they plant the seeds of valuable trees; for probably some of their caches are never found. Then, too, many a squirrel comes to grief before it has had a chance to benefit from its storage proclivities.

A female Gray Squirrel watched in Yosemite Valley on May 19, 1919, was spending much of her time on the ground seeking out acorns buried (presumably by the same animal) during the preceding autumn. The squirrel went along hesitatingly, with her nose close to the ground, moving this way and that, as though she were smelling for the nuts. When she found a promising prospect she would whisk aside the winter's deposit of pine needles with her forefeet and then dig rapidly down 2 inches or less, pulling the earth toward her and heaping it beneath her chest. If an acorn was found, the squirrel would dislodge it with her teeth and then and there, sitting back on her haunches, immediately shell out and eat the nut. In one instance an acorn which was dug up was buried again in a new place ten feet away. The squirrel tamped the earth down over it with her nose and forepaws and then raked pine needles over the place. Only about one in three of the places which were prospected yielded acorns; so we may infer that these animals are not infallible. It would seem that the sense of smell must be relied upon to find these 'planted' acorns. After the winter's snow, rain, and wind, with much movement of oak leaves and pine needles on the surface of the ground, accurate memory of the sites is apparently out of the question. Furthermore, one of the acorns which the squirrel dug up and replanted, and which one of us later examined, had a distinctly sour odor, clearly perceptible to our gross sense of smell.

In this particular instance we have support for the belief that instinct rather than reason controls the squirrel's food-getting activities. There was no real need for this squirrel's activity, because there had been an extremely abundant crop of acorns on the black oaks during the preceding winter and acorns were still to be found on the ground in large numbers. The squirrel could have found much more forage in a given period of time by moving a short distance into the oak forest; yet she remained and foraged beneath the pines in the instinctive manner which serves her in a season of shortage.

In Yosemite Valley on October 8, 1914, a large 'bracket' fungus growing at a height of 15 feet on the trunk of a black oak showed many tooth marks of Gray Squirrels (and possibly some made by Flying Squirrels); there were also many 'crumbs' on the ground beneath. The tooth marks were mostly on the under surface; the top surface was tough and leathery. The free edge had been gnawed literally to shreds and the indication was that most of the mass had been eaten away. When found, the base against the tree was 9 inches (230 mm.) wide and 3-1/2 inches (90 mm.) high, and the mass projected out 5 inches (120 mm.) from the trunk. The taste, to the naturalist's tongue, was not unpleasant, somewhat like raw mushrooms, but rather woody. At other times gray squirrels were observed digging a tough kind of fungus out of the ground.

The conduct of the California Gray Squirrel in cutting down the green cones of the two important lumber trees, yellow and sugar pine, has been commented upon adversely by foresters. The claim is made that the squirrels consume so much of the seed that not enough is left for natural reforestation. This point, so far as we know, has not been thoroughly tested by experimentation; the issue now stands between the judgment of the forester on one hand, and that of the naturalist on the other. We do know that many other factors, such as parasitism of the growing trees by mistletoe or fungus, destruction by fire started by lightning or by human agency, and killing of young growth by grazing, operate to limit the numbers of the trees. And of the seeds which remain in cones on the tree, a very considerable percentage is attacked by certain insects whose young subsist on the embryo plant. The squirrels thus comprise but one factor out of many; attention is likely to be focused upon their work because of its conspicuousness; it is carried on in the open. Other agencies fully as significant operate in an unobtrusive manner, and their importance is thus likely to be underestimated.

It is our opinion that in most places where natural conditions still obtain, the necessary reseeding progresses as fast as is possible anyway, and that the activities of the squirrels do not retard the regeneration of the forest. Where man has interfered by logging off much of the timber or by close grazing, the case may be different.

One resident at Snyder Gulch stated to us that he believed that Gray Squirrels indirectly do damage to sugar pines by leaving heaps of cone scales at the bases of trees when shucking out seeds. When a forest fire sweeps over the country these piles take fire easily and start 'burns' at the bases of the trees. As bearing on this contention we noted many sugar pine trees with kitchen middens at their bases, and many trees showed basal burns which may have been made in the manner indicated. At Hazel Green there were heaps of scales about several oak trees, and at one particular tree there was a kitchen midden fully 18 inches high within the hollowed base of the tree.

The California Gray Squirrel, so far as known, rears but one brood of young each year, and this is brought off during the early summer months. None of the female squirrels which we obtained contained embryos; but litters elsewhere are known to range from 2 to 4. By mid-summer the young animals are beginning to appear abroad, being then, on the average, about half the size of adults.

The Gray Squirrel population is affected by a number of factors. Birds of prey capture a certain percentage of the animals; some young are killed by falling out of the nest; other young animals are caught by dogs, and in wild country probably also by native carnivores; disease greatly reduces the ranks of the Gray Squirrels from time to time, as is known to have been the case in other places in California; and, most important of all, the downward fluctuations in the crops of seeds on the principal food trees operate to limit the population.

Locally, interference by man is operating to reduce the pressure exerted by native carnivorous species on the Gray Squirrel. In Yosemite Valley, the government authorities have favored the elimination of coyotes, bobcats, and other natural checks. This has evidently worked to the advantage of the Gray Squirrels, and accounts, in part at least, for the great numbers of animals present during certain recent years on the floor of the Valley. To our way of thinking, this sort of interference is doubly disadvantageous. A National Park ought to be a "natural" park, where the "balance of nature" can remain undisturbed.