MARIPOSA CHIPMUNK. Eutamias merriami mariposae Grinnell and
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.
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
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
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
indicateddull 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.