ALPINE CHIPMUNK. Eutamias alpinus (Merriam)

Field characters.—Smallest and palest colored of the Yosemite chipmunks (head and body about 4 inches long, tail scarcely 3 inches long). (See comparative measurements in footnote 15, p. 177.) Usual chipmunk pattern of coloration; sides of body pale buff; tail showing more yellowish buff than black. (See pl. 3b). Voice: A wiry, not loud, sweet repeated frequently; this sometimes modified to whit when uttered more slowly and with emphasis; also a low chuckle.

Occurrence.—Common resident of Hudsonian Zone, ranging locally into Alpine-Arctic. Recorded on Mount Hoffmann and on Mount Clark, and from Glen Aulin and near Vogelsang Lake eastward to Mono Pass and Ellery Lake. Seldom below 8500 feet altitude. Lives chiefly among rocks, sometimes about fallen logs; climbs trees but rarely.

The Alpine Chipmunk is the smallest and palest colored of all the chipmunks occurring in the Yosemite section. It lives habitually at higher altitudes than do the other species. In only one place was it observed below 8000 feet; the greater part of the population of the species lives far above that altitude.

Only one other chipmunk, the Tahoe Chipmunk, is found regularly within the territory inhabited by the Alpine Chipmunk. From that species the Alpine may be distinguished by its smaller size and paler tone of coloration and by its marked preference for the rocks. (Sec pl. 3b). Furthermore, alpinus shows much less curiosity than does its relative. If the observer makes a squeaking noise with his lips, the Tahoe Chipmunk will usually be attracted to investigate, whereas the Alpine Chipmunk will either pay no attention whatsoever or else hasten away.

Along the eastern margin of the range of the Alpine Chipmunk is to be found the Mono Chipmunk, a species of only slightly larger size but of somewhat more brilliant coloration. Both may be seen about rocks, and then only close scrutiny of individuals will enable an observer to distinguish between the two. However, alpinus has not been found east of Warren Fork of Leevining Creek and Mono Pass and monoensis is not known to occur west of those stations. At Glen Aulin the range of the Allen Chipmunk meets that of the Alpine. But the latter is only about half the bulk of the former and its coloration is obviously lighter, so that no difficulty will be experienced in distinguishing these two species.

The range of the Alpine Chipmunk comprises chiefly the Hudsonian Zone, including the 'tongues' of that zone which extend westward from the main Sierran crest to such outstanding peaks as Mount Hoffmann and Mount Clark. The species ranges upward beyond the limits of the main forest, and in a few instances was noted above the highest indication of timber line and hence within the Arctic-Alpine Zone. For example, one was seen at 11,500 feet altitude on Parsons Peak.

This species inhabits for the most part rocky situations, either the large masses of slide rock on the cañon sides or the scattered boulders within the rather open stands of lodgepole pine. Not infrequently it is seen scampering over and about logs lying on the ground, and in a few instances individuals were seen in trees. On Mount Hoffmann an Alpine Chipmunk was seen 3 feet above the ground in a white-bark pine, and another at Ellery Lake was 6 feet up in a lodgepole pine; at Young Lake one of the animals was seen to climb several feet up into a lodgepole pine on the lake shore. But the rock piles constitute the accustomed habitat; individuals traverse these with great facility, and venture much farther into such places than do the Tahoe Chipmunks. Although we found no nests, we believe that the Alpine Chipmunk finds its shelter and suitable breeding dens either amid the rocks or in the ground beneath them.

Bearing in mind the liveliness of chipmunks in general, the Alpine Chipmunk must be put down as exhibiting the extreme of agility, so nimbly and lightly does it skip about from place to place in carrying on its daily activities. When running on the ground it usually holds the tail up vertically and so gives the impression that this member is larger and longer than actual measurements show it to be. When a chipmunk is perched on some rock, and calling, its tail is usually jerked upward at the instant each note is given.

This chipmunk does not seem to be so talkative as some of its relatives. Certainly upon many occasions when the presence of an observer would provoke other species to loud and persistent chipping, alpinus gave few or no notes. Its calls as compared with those of the Tahoe Chipmunk are fainter and higher pitched. Once learned by an observer they can be used with considerable certainty in identifying the species. A common call is a repeated sweet, sweet, sweet, etc., with rather short intervals between the notes and continued for varying lengths of time. If badly frightened a chipmunk will utter a startled whip-per'r'r as it runs to shelter. On occasion a low chuckling note is given, similar to the hollow-sounding 'barks' of the larger species.

The Alpine Chipmunks, despite their boreal home, are active through a rather long season. Our earliest contact with them seasonally was on June 28, 1915, when a number were noted on Mount Hoffmann. As the breeding season was then well advanced or nearly over it seems likely that they had begun to be active much earlier in the year. On October 11, 1915, several of the animals were seen still abroad in the vicinity of Ten Lakes. At Tuolumne Meadows we were told that during a storm in mid-September the Alpine Chipmunks had taken to cover, but that they had reappeared as soon as snow ceased to fall. The individuals seen on Mount Hoffmann were, in several instances, running across the snow banks. Judging from observations made elsewhere upon other species of chipmunks, it seems probable that weather rather than temperature alone is the determining factor in limiting the season of activity for the Alpine Chipmunk.

The time of mating is unknown. Two females collected June 30, 1915, contained 4 and 5 large embryos, respectively, and others captured between July 5 and 17 had been recently suckling young. Males collected in July gave evidence that the period of sexual activity was well past. On July 30, young individuals were abroad around Tuolumne Meadows. A young female weighing 19.5 grams, which is only about half of the weight of an average adult, was collected at 10,500 feet altitude on Mount Florence, August 20, and two individuals obtained on Mount Clark on August 22 were scarcely two-thirds grown. By early October young-of-the-year had reached nearly or quite the size of adults.

The Alpine Chipmunks obtained at the end of June and in early July are passing from the much worn and dulled winter pelage into the more brightly colored new coat. By October this new pelage is completely assumed and is then not only longer and denser but more grayish in tone than when it first starts to appear.

The habit of pursuing one another, noted of other chipmunks, is conspicuous in the present species. A pair will go at great speed, one individual after the other, up over logs and rocks and down through crevices, the two keeping always only a few inches apart. This habit is marked long after the close of the mating season. One explanatory theory states that this practice serves to keep the animals 'in training,' so that when a real menace threatens, as, for example, when a marauding Least Weasel makes its appearance, a chipmunk will find itself in optimum condition for escape to some safe refuge. Another suggestion offered is to the effect that this habit is acquired in order that when male pursues female for the purpose of accomplishing the mating act, only the swiftest males will succeed. If swiftness be a point of advantage to the species, then a sort of sexual selection by which swiftness will become an accentuated trait, will here be operative.

There is always more or less competition between the members of a species in the struggle for existence, and considerable individuality in behavior is exhibited whenever several animals of any one species are gathered at close quarters, as when they are attracted by a common food supply. This individuality was illustrated at Tuolumne Meadows one afternoon in late September, when several Alpine Chipmunks were seen contesting with one another for possession of some scraps of bread which had been discarded from a lunch. At first but one chipmunk was in evidence and he busied himself with a piece of the bread. He was soon observed by another of his kind who shortly arrived on the scene, and this second animal made an attempt to gain possession of the piece held by the first. Being unsuccessful, the second then found another fragment for himself. Later a third and then a fourth chipmunk arrived. Only one animal would eat at any particular piece at one time; if another attempted to join in, a contest would ensue. Sometimes the original possessor successfully defended his rights, sometimes the interloper gained control. Just as among human beings, one, for the time, might dominate the group, another might be bullied about by all, and the others would hold their ground between these two extremes.

In spite of the seemingly barren appearance of its chosen habitat the Alpine Chipmunk finds, at the proper season, an abundance of food in the way of ripe seeds. But the season of harvest is short and many of the seeds are of very small size; to secure these seeds in adequate quantity both for immediate use and for storage therefore requires a rare concentration of effort and a high degree of industry on the part of the harvesters. This industriousness is fully apparent if a person takes the time to watch the animals from a vantage point where his presence does not, through fear or alarm, distract the attention of the chipmunks. Analyses of cheek-pouch contents are instructive in this connection also; and the following selections seem worth placing on record here.

(1) Fletcher Creek at 10,000 feet altitude, September 4: some fragments of a brown fungus.

(2) Colby Mountain at 9200 feet, October 9: two seeds of pine (thought to be silver pine).

(3) Ten Lakes at 9200 feet, October 8: 47 seeds of a grass (stipa).

(4) Ten Lakes at 9200 feet, October 11: 324 seeds of sedge and 1 of stipa.

(5) McClure Fork at 9200 feet, August 29: 165 seeds of sedge and 24 of galingale; total 189.

(6) Mount Hoffmann at 10,300 feet, June 30: 388 seeds of sedge and 1 of pussy-paws.

(7) Mount Florence at 10,500 feet, August 21: 1113 seeds of willow-herb, 1 of pussy-paws, 19 of stipa, 36 of galingale; total 1169 seeds.

(8) Mount Clark at 10,500 feet, August 22: 27 seeds of pussy-paws, 1 of rush, 1080 of a very small undetermined seed; total 1108 seeds.

(9) Mount Florence at 10,500 feet, August 21: 1550 seeds of sedge, 5 of stipa; total 1555 seeds.

(10) Ten Lakes at 9200 feet, October 9: 4796 seeds of pussy-paws, 174 of sedge; total 4970 (counted seed by seed into groups of 10 and these into 100's and 1000's).

The seeds of the plant known as pussy-paws (Spraguea umbellata) seem, wherever obtainable, to be especially sought after by chipmunks. These seeds are very small (0.7 to 1.2 mm. in diameter), flattish, smooth, and glistening black; and they prove exceedingly elusive to human handling. The fact that the mass of seeds in a chipmunk's cheek pouches is invariably free of chaff or any other useless material bespeaks a marvelous degree of dexterity on the part of the harvester. When we note that one load contained practically 5000 seeds, and recall the complicated nature and rapidity of the movements of the forefeet, lips, and tongue which must be involved in the act of gathering seeds, our wonder at the effectiveness of the chipmunk's nervous and muscular organization is beyond expression.