TAHOE CHIPMUNK. Eutamias speciosus frater (Allen)

Field characters.—Size medium¹⁵ for a chipmunk (head and body 4-1/2 to 5 inches, tail 3-1/4 to 3-3/4 inches long). (Sec pl. 3e). Tail bushy, flat-appearing, the long hairs on each side bright brown at bases, then black, with buffy white at tips. Back with nine alternating light and dark stripes, the outermost light stripe on each side being conspicuously pure white; side of head with five sharply defined stripes, alternately dark and white from above downward; sides of body bright reddish brown; top of head and rump grayish; under surface of body whitish. Distinguished from mariposae, quadrimaculatus, and senex by smaller size, and from monoensis, pictus, and alpinus by larger size; coloration brighter than in any of the others, with light stripes on sides of head, and back whiter. Voice: A moderately high-pitched whisk repeated at intervals; also a very shrill tsew, and, when frightened, a rapid series of notes, pst-pst-pst-a-ku.

Occurrence.—Common resident in Canadian and Hudsonian zones on both slopes of Sierra Nevada. Recorded from Crane Flat and near Chinquapin eastward across mountains to Walker Lake. Extreme altitudes, 6200 and 10,350 feet. Lives in forest, foraging both in trees and on ground, rocks, and logs, but habitually takes refuge in trees, going 40 feet or more above ground.

The Tahoe Chipmunk is the most widely distributed and perhaps the most abundant of the seven species of chipmunks inhabiting the Yosemite section.¹⁵ Its range embraces all of the forested portions of the "high Sierras" between altitudes of 6200 and 10,350 feet. In the wooded territory immediately above Yosemite Valley, as at Glacier Point and back of Yosemite Point, the species is abundant, while farther to the east, at Merced Lake and Tuolumne Meadows, it is also well represented.

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¹⁵Since relative sizes of the whole animals, and proportions of foot, ear, and tail, constitute important characters of the seven species of chipmunks found in the Yosemite section, we give here a table of their measurements and weights. These are based upon ten adult individuals of each species, all of these having been captured within the section.

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The Tahoe Chipmunk is the only one of the local chipmunks which habitually takes refuge well up in trees. This trait alone will, as a rule, serve to distinguish the species from any of its relatives. In point of size the Tahoe Chipmunk stands midway among the seven species of the region, being smaller than the Mariposa, Long-eared, and Allen chipmunks and larger than the Mono, Alpine, and Sagebrush chipmunks. The coloration of the Tahoe Chipmunk is brighter reddish in general effect than that of any of the others, and the light stripes on the sides of the head and back stand out as being more definitely or clearly white. (See pl. 3.)

In the lower part of the Canadian Zone the range of the Tahoe Chipmunk overlaps that of the Long-eared. (See fig. 28.) Throughout most of that zone the Tahoe and Allen chipmunks occur on common ground, while the Hudsonian Zone is shared by the Tahoe and Alpine chipmunks. Along the eastern slope of the mountains the Tahoe Chipmunk occurs in localities tenanted by the Mono Chipmunk and in a few places its range touches that of the Sagebrush Chipmunk. But at no place did we find the Tahoe and Mariposa chipmunks together. On the Yosemite Falls trail, mariposae has been recorded at Columbia Point (5000 feet) while frater has been seen only 1600 feet higher, at the top of the zigzags. But this difference in altitude almost anywhere else than on the nearly vertical walls of the Yosemite gorge would mean a geographical separation of several miles.

Fig. 28. Cross-section of the Sierra Nevada through the Yosemite region showing zonal and altitudinal distribution of Chipmunks (genus Eutamias).

It is difficult to determine with any degree of exactness the population of mammals, even of such diurnally active species as chipmunks. Data obtained from field censuses are not so reliable for mammals as for birds. During the springtime, the regular singing of the male birds makes locating and enumerating individuals simple; then, too, in other seasons the call and flock notes of each species are uttered with more or less frequency. Not so with chipmunks! When alarmed these animals will call for long periods and then, if there is no new cause for excitement, they will be perfectly quiet for an even longer time. Many times while we were afield in favorable surroundings we did not hear or see a single chipmunk. Then, upon the occurrence of some unusual sound, several would call at once from different directions, all voicing curiosity. In brief, then, while we have census figures to offer, they are not so definitely dependable and show greater discrepancies than do those for most birds. At Porcupine Flat on June 28, 1915, four Tahoe Chipmunks were noted during a single hour, while on two other occasions, once at the same locality and again near Mono Meadow, seven of these animals were recorded during five hours of active observation. It is our impression, gained from extensive field experience, that the Tahoe Chipmunk has its maximum of abundance in the Canadian Zone on the west slope of the Sierras. Again calculating largely from impressions, we would set down the spring population of the Tahoe Chipmunk, before emergence of the young-of-the-season, as about two an acre or 1280 a square mile through the forested portions of the Canadian Zone. In the tree-covered portions of the Hudsonian Zone the population is only about one-half as great. In the late summer when the young are out and all ages are represented, the impression of 'swarms' of chipmunks is given, especially in those localities where forage conditions are most favorable.

The Tahoe Chipmunk shows greater latitude in the matter of its local range than does any of the other Yosemite chipmunks. It runs around a great deal on the ground and over fallen logs, and at times it climbs the brush plants to harvest the crops of seeds or fruit. But the most notable feature in the behavior of the species is its tree-climbing propensity. It habitually goes up into trees at the first hint of danger, climbing many feet above the ground. Even when not frightened the animals do much running around in trees. Frater is an adept climber and can go rapidly up the side of a perpendicular trunk, even up such smooth-barked trees as young lodgepole pines and firs. When a frightened animal has gained what it considers a safe height above the ground, it will usually lie quietly on the top of a horizontal branch and peer over the side and down at the scene of its late scare. Its brown and streaked coloration matches so well the various shades of color of the trunk and branches that the animal's location might easily be overlooked were it not for the plume-like tail which often hangs down to one side of the branch, waving back and forth with seeming carelessness.

Tahoe Chipmunks are able to run down comparatively smooth-barked trees head foremost with ease and safety, either at great speed, or moving slowly a few steps at a time. This bespeaks great efficiency in the structure and use of the claws and toes. Individuals have been seen to leap short distances from one branch to another; but, in this respect, the ability of even this most arboreal of our chipmunks is inferior to that of the Gray and Red squirrels.

At Walker Lake one day in September one of our party was walking past a small Jeffrey pine when a Tahoe Chipmunk suddenly dropped to the ground from a height of ten or fifteen feet in the tree. The animal seemed unhurt and quickly made off and climbed a white fir in the vicinity. A jump to earth of considerable magnitude seemed to have been undertaken voluntarily, as an extreme measure of safety, perhaps, and accomplished without injury.

It is not uncommon to see two chipmunks engaged in a play-like pursuit of one another which may last for minutes at a time and carry the two over and beneath logs, through brush, across open places in the forest, and not infrequently up, around, and down the trunks of one or more trees. This habit is not peculiar to the Tahoe Chipmunk, but is indulged in by most, if not all, of the other species. Whether it is pure play, or whether it is part of the courting behavior, we do not know, but its occurrence at various seasons of the year and the fact that young animals often engage in it, indicate that it is not related immediately to mating. As pointed out in the chapter on the Alpine Chipmunk, there are various and diverse relations borne between individuals of the same species, and some of these seemingly mild-mannered chases may, in actuality, he instances where one individual has invaded the small area of territory over which some other chipmunk already exercises 'property rights' and is 'defending title.' The study of behavior in chipmunks in a state of nature would prove a fascinating one, and the plentiful population of these animals at easily accessible spots in the Yosemite region affords excellent opportunities for such a study.

The fact that the Tahoe Chipmunk is the only one of seven local species which habitually climbs high in the trees is a point of evidence that restriction to a particular type of habitat or mode of behavior does not always rest upon the possession of conspicuous special structural features of an adaptive nature. So far as can be seen by an examination of specimens in hand, none of the other species of chipmunks is physically incapacitated for tree climbing; in fact, individuals of these others are occasionally observed well up in the trees. There doubtless are minor features of structure, associated with a different psychology, which account for the differing traits indicated. Age-long segregation, in separate areas of differentiation, of the several stocks may be the basis of this divergence of habitat preference. The shifting of climatic barriers, with the resulting migrations of populations, has thrown the species together as very near neighbors or as actual companions. Fatal competition is prevented as a result of these initial predilections, whereby frater favors the trees, alpinus the rocks, and senex and quadrimaculatus the brush patches and logs.

A Tahoe Chipmunk three-fourths grown was caught lightly by one front paw in a mouse trap at our Lyell Cañon camp in late July, 1915. One of the members of the party kept the animal in captivity for a time to learn something of its habits. From the time of its capture the chipmunk never attempted to bite, although at first it struggled when handled. Later, when permitted to run about camp and even to climb trees it was recaptured easily. The first night in captivity the animal was placed in a roll of cotton in a pail. During the night it worked out of the cotton and became very cold and numb, in fact it was seemingly lifeless; but a little warming soon revived it completely. The chipmunk drank and ate readily in captivity, taking about a quarter of a teaspoonful of water and several pinches of rolled oats daily. The water it sucked, not lapped, into the mouth; but sometimes it would put its tongue out into the water before actual drinking began. Rolled oats seemed to supply its needs in the way of food, but it also accepted various other items from the camp breakfast. Beans and sugar were eaten readily. The chipmunk would often lick the hands of a person holding it, probably because of the salt deposited on the skin by perspiration.

When holding food materials, this chipmunk used its forefeet like hands; usually it employed both feet, but sometimes only one. If hungry it would stuff kernels of grain into its cheek pouches, but without putting its paws clear into the mouth. Again, after the pouches were crammed with food, it would slip out one grain at a time (and this also was done by working the muscles of the jaws without help from the paws), and nibble the kernel while holding it in the paws.

Much of the activity of chipmunks in summer and fall has to do with the getting and storing of food materials against a season of the year when such supplies are scant or lacking. Although we did not find any large food cache of any of the chipmunks it is probable that the animals do lay by stores in considerable quantity in particular spots. But whether or not they accumulate much food material, we do know that chipmunks are accustomed to bury seeds and nuts of various kinds, a few in a place or singly. After having gathered one or more such articles the chipmunk, using its forepaws in the digging, will excavate a small hole, often deep enough to conceal the animal's head from the view of a person off to one side. Then the contents of the cheek pouches are transferred to the hole, the hole is filled up, and the surface more or less smoothed over and patted down. Some, at least, of such caches are subsequently opened by the chipmunks, as we ourselves have witnessed. Whether the recovery is made by the animal which originally buried the material is not known, though this is believed usually to be the case. A considerable number of the seeds, however, are not dug up by any rodent, and being planted at a proper depth, begin to germinate, when conditions of warmth and moisture are right, and give rise to seedling plants. In this way the chipmunks doubtless atone in full for the toll which they levy on the forest trees and brush plants in the way of seeds actually consumed. The manner in which the chipmunks relocate stores which have been buried is not known definitely, but the sense of smell is probably of important service.

The chipmunks, constituting a group of rodents usually thought of as tree-dwelling animals, are in reality more closely related to certain of the ground squirrels than to the tree squirrels. One feature possessed in common is the cheek pouch. This is a thin membrane-like sac, one on each side of the face beneath the outer furry skin and opening inside the mouth. Seeds or nuts can be passed from the mouth to the pouches or vice versa merely by action of the cheek muscles and tongue, without aid from the forepaws. The Gray and Red squirrels have no cheek pouches of any sort.

When foraging, the Tahoe Chipmunk is likely to be seen in a wide variety of situations. In the Canadian Zone it was often noted climbing about in different sorts of brush plants to gather the seeds or fruits. Some food, such as scattered pine seeds, certain kinds of fungi, and scraps from persons' lunches is sought on the ground. In the fall months many different members of the squirrel family busy themselves in harvesting grass seed, and the Tahoe Chipmunk was sometimes seen so engaged. At Porcupine Flat, in late June, the animals were at work on the cones of the lodgepole pine. At Ten Lakes, in October, two of these chipmunks which had their faces smeared with pitch were encountered, suggesting that the animals had been working on unripe cones.

The contents of the cheek pouches of 10 individual Tahoe Chipmunks, collected for specimens, were saved by us for analysis. In 6, seeds of coniferous trees exclusively were represented; in 5 of these cases the seeds were those of the Jeffrey pine, the remaining one being (doubtfully) of the lodgepole pine. The numbers of pine seeds which were contained in the cheek pouches of individual animals varied from 1 to 20, the latter (of Jeffrey pine) constituting seemingly the full capacity of the two cheek pouches of a chipmunk.

The other 4 sets of contents of cheek pouches gave analyses as follows: (1) Fragments of a brown-colored fungus; (2) 62 hulled seeds of a grass, probably wild brome; (3) 90 seeds of black bindweed (an introduced plant); (4) a mixed lot of seeds including those of a geranium, a phacelia, a borage, and a sedge.

The season of activity for this chipmunk extends through the greater portion of the year. Even the light snows of early winter do not drive all the individuals into hibernation, although they probably all disappear with the first heavy snowfall of the season. In the spring, they are out and active when travelers are first able to climb to the higher levels, in May. The little fellows are then to be seen skipping over the packed snow banks between logs and tree trunks with no seeming discomfiture.

Few data are available concerning the exact time or duration of the breeding season in this or any of our other species of chipmunks. Among ground squirrels one species is known to take somewhat less than one month for gestation, and it seems probable that the period is at most not longer in chipmunks. This would require, on the basis of young being born in late June or early July (as shown by the data given beyond), mating toward the end of May. At this season; though the "high Sierras" are still fairly well covered with snow, the daily temperature reaches a relatively high point, and spots of bare ground are beginning to appear.

Our records for the Tahoe Chipmunk, based upon the taking of specimens, show pregnant females as follows:

Many young were abroad at Tuolumne Meadows by July 31, 1915. The number of young in a litter we may infer to vary from 3 to 6, and to average about 4.