Animal Life in the Yosemite
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MARIPOSA CHIPMUNK. Eutamias merriami mariposae Grinnell and Storer

Field characters.—Large for a chipmunk (pl. 3f); length of head and body about 5-1/4 inches, tail 4-1/2 to 4-3/4 inches (see table in footnote 15, p. 177, for detailed measurements). Dullest colored of all the Yosemite section chipmunks; light stripes indistinct, not white; spot behind ear grayish; general tone of coloration dull reddish brown in summer coat and grayish brown in winter. Voice: A hollow-sounding bock, repeated at regular intervals; when excited, a high-pitched whisk, repeated; also a rapid sputter of four or more syllables.

Occurrence.—Resident in small to moderate numbers in Upper Sonoran and low Transition Zones, on west slope of Sierra Nevada. Recorded from Mast (700 feet altitude near Pleasant Valley), eastward to Columbia Point (altitude 5000 feet) on north wall of Yosemite Valley. Inhabits brush and trees, especially oaks, rarely ascending latter to 25 feet or so above the ground.

The Mariposa Chipmunk is the local representative of a group (the Merriam Chipmunks) which is found commonly at middle altitudes in the mountainous portions of southern California. This is the only chipmunk known to occur on the floor of Yosemite Valley, and there, as well as at other stations within its local range, it is remarkably scarce as compared with the number of chipmunks higher in the Yosemite section.

The westernmost station of record for the Mariposa Chipmunk is Mast, in the lower Merced Cañon. Upon none of our visits to Pleasant Valley, only a little lower down, did we get any trace whatsoever of chipmunks. The animals were moderately common in the mixed stands of trees and brush near the old Merced Gold Mine mill west of Coulterville, and a number were recorded at El Portal. In Yosemite Valley, as at Rocky Point and similar places along the sides of the Valley floor, the rough talus slopes grown over with manzanita and golden oaks were found to be the best locations in which to seek the animals. No Mariposa Chipmunk was seen higher than Columbia Point, altitude 5000 feet, on the Yosemite Falls trail.

Compared with other chipmunks of the region this species is the largest and the least strikingly colored. (See pl. 3f). There is a prevailing dullness to the pelage, especially to the gray winter coat, even more noticeable than in the Allen Chipmunk. We did not actually see Mariposa Chipmunks at any locality where any of the other species occurred. It seems not unlikely, however, that the range of the Mariposa will be found to touch that of the Long-eared Chipmunk in certain places. The Mariposa Chipmunk is much duller colored (decidedly less brightly brownish), as compared with the Long-eared, and the spot at the hinder base of each ear is only imperfectly indicated—dull gray instead of pure white; the ear itself is decidedly smaller, not so tall.

It seems likely that those Mariposa Chipmunks which live in the Upper Sonoran Zone do not actually hibernate at any season of the year. They probably remain in their retreats during rainstorms and come out on warm days at any time during the winter months. But those individuals which live in Yosemite Valley and elsewhere in the territory where snow remains for some time during the winter months (Transition Zone), do, in all probability, hibernate. Thus at El Portal, in the fall and early winter of 1914, Mariposa Chipmunks were out and active until December 7, perhaps later. The latest seasonal record on the wall of Yosemite Valley is for November 19 (1915). None was seen anywhere in the Valley during our intensive work there in December, 1914; nor was anything noted of the animals during a visit to the Valley at the end of February, 1916.

On the whole, the Mariposa Chipmunk seems to be a reclusive species. It adheres to a dense type of vegetational cover, where also the range of the observer's view is short. We found that occasional individuals would chip noisily when one of us 'squeaked' at them, but more often the chipmunks became silent after the first bit of noise or movement on our part. At Blacks Creek one of several of these chipmunks to which we 'squeaked' came within close range. The animal sat partly hidden from view in a thicket and called bock, bock, bock, in long series about as fast as a person could pronounce the syllables easily. Usually each note was accompanied by a sidewise wave of the tail. When frightened by a movement on the part of the observer, the chipmunk gave a rapid series of sibilant notes and dashed off along branches toward some refuge, after which it remained silent and gave no clue to its new location.

The Mariposa Chipmunk, like others of its kind, is given to burying food supplies in small pockets in the ground. Under some manzanita brush on a hill west of the McCarthy ranch and about 3 miles east of Coulterville, we found these caches common, though the animals themselves were notably successful in keeping out of sight.

The favorite haunts of this species in the foothill country seem to be the mixed growths of brush and small trees. Seldom did we find them in continuous or pure chaparral. They do not seem to affect the monotonous stretches of greasewood at all. On several occasions the animals have been seen in oak trees, in one instance about 30 feet from the ground.

A common resort for chipmunks in the vicinity of Dudley was along the rail fences bounding the ranches and bordering the hillside chaparral. In places like this, on July 22, 1920, 5 chipmunks were checked in a 3-1/2 hours' census walk. A rattlesnake coiled under the lowest rail of a fence was found to contain a partially digested chipmunk; the snake had evidently found the fence a favorable place for his own foraging.

The actual floor of Yosemite Valley does not afford much appropriate cover for the Mariposa Chipmunk. The animals live on the boulder talus overgrown with brush and golden oaks along either wall; they are most numerously represented on the warmer north side of the Valley. In 1915, several chipmunks lived in woodpiles near certain of the buildings in the Village, and they came regularly to take nuts and other food placed out for them in front of the village barber shop. Once, on the north side of the Valley, one of these chipmunks was seen to run across the road and climb the slanting trunk of a willow which stood only about fifty feet from the bank of the Merced River.

The breeding season of the Mariposa Chipmunk begins very early in the spring. A female captured at Blacks Creek, May 10 (1919), was already suckling young; another individual taken that same day was a young animal of the current season already over half-grown. On June 8, 1915, a half-grown young-of-the-year was collected on the ridge of hills 3 miles east of Coulterville, and another a little larger was taken on Smith Creek July 16, 1920. All these young animals have the characteristic pelage of young chipmunks, soft and rather scanty, with colors darker, more blackish, than in adults. A female taken in Yosemite Valley July 29, 1915, was a young-of-the-year, of nearly adult size. It had assumed its first summer coat. The Mariposa Chipmunk evidently breeds earlier than does any of the other local species of chipmunk; this fact is consistent with the greater warmth of the animal's habitat. Its young are abroad in the spring long before the young of high-mountain species have been born.


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

grinnell/mammals61.htm — 19-Jan-2006