The Oregon chipmunk is one of the common species showing marked response to these local climatic conditions and is the darkest of all the many species of chipmunks in the Western States. This chipmunk is one of several geographic races into which the species is divided by changing environment. The species, as a whole, ranges along the west coast from British Columbia to Lower California, and the races at the extremes of the line differ much in color.
As befits a habitant of the humid forested region, the Oregon chipmunk is robustly built and distinctly larger than the other chipmunks of the Western States. It is common and generally distributed throughout this region, occurring from among the drift logs along the ocean beach to above timberline on the Cascade Mountains. Within these limits it frequents almost every variety of situation. It occurs in the midst of gloomy forests of giant spruces, cedars, and firs, but is particularly fond of old fences and brush patches on the borders of farm clearings in the valleys as well as the vicinity of rocky ledges, brush piles, and fallen timber, where the low thickets offer a variety of food-bearing plants and ready shelter.
On the mountains it is most numerous about rock slides and “burns” or other openings in the forest. Several pairs usually haunt the vicinity of old sawmills and of mountain cabins. Like others of their kind, they are alert and vivacious, varying in mood from day to day, but always interesting. At times they are excessively shy and retiring, and a person might spend a day in their haunts without seeing or hearing one, although it is safe to say that the intruder had been seen and every foot of his progress noted by the chipmunks. On another day, perhaps because the sun shines more brightly and nature is in a happier mood, the animals appear on all sides. Their slowly repeated sociable chuck, chuck, is heard from the depths of the brushy covert as well as from the tops of stumps, logs, rocks, or other lookout points where they sit to view their surroundings. If alarmed they utter a sharp, birdlike chirping note as they vanish in the nearest shelter. As one moves about in their haunts he may now and then see one appear for a moment above the undergrowth in a tall bush, on top of a stump, and sometimes even mounting a few yards up a tree trunk to observe the cause of the disturbance, only to vanish quickly.
They are always skirmishing for food, and carrying it in their cheek pouches to hidden stores. On the approach of winter this activity becomes very marked. A surprising variety of fruits and seeds are eaten and stored, among them the salmonberry, red elderberry, black-capped raspberry, thimble berry, blackberry, blueberry, gooseberry, thistle seed, dogwood seed, hazelnuts, acorns, and others. They have favorite feeding places, such as the top of a stone or stump or the shelter of a log where they carry nuts or other seeds. These places are always marked by little piles of empty shells or chaff from seeds. About ranches they raid grain fields and other crops, sometimes in numbers sufficient to do considerable damage.
In sheltered spots they make underground burrows with nest chamber and store-rooms excavated along the passages. They usually retire to these dens to hibernate during the last of September or first of October, and appear again about March or April, often long before the snow disappears. During fall and early winter they are sometimes seen running about over newly fallen snow. One which was dug from its winter quarters in British Columbia the last of November would move about slowly and sleepily if teased, but when left undisturbed would curl up and go to sleep again. This indicates the difference between the light and often broken hibernation of chipmunks and the deep lethargy which possesses ground squirrels in the North at this time. Toward the southern end of their ranges neither chipmunk nor ground squirrel hibernates. They mate soon after they awake from their winter sleep, and the young, two to five or six in number, are born from April to June. Whether more than one litter is born during a season, is, like many other details concerning the lives of these attractive animals, still to be learned.
THE PAINTED CHIPMUNK (Eutamias minimus pictus and its relatives)
(For illustration, [see page 543])
The preceding sketch tells how the Oregon chipmunk, living under a cool, humid climate, in a region of great forests, has responded to its environment by developing dark colors and a robust physique. The painted chipmunk of the Great Basin has given an equally perfect response to entirely different conditions. It is one of the geographic races of a species peculiar to the sagebrush-covered plains and hills from the Dakotas across the Rocky Mountains and the Great Basin region to the east slope of the Cascades and the Sierra Nevada. Its home is on treeless plains, in a climate characterized by brilliant sunshine and clear, dry air. In this environment the painted chipmunk has developed a smaller and slenderer body than the Oregon species, and strikingly paler colors.
These differences in physique are accompanied by equal differences in mental and physical expression. These little animals are exceedingly alert and agile, darting through dense growths of bushes with all the easy grace of weasels. When running they hold the tail stiffly erect. When alarmed they utter a shrill chippering cry, especially when darting into shelter. They also have a chucking call, uttered at intervals, which may be used merely as a note of sociability or to put their neighbors on the alert.
Although one of the most distinctive animals of the sagebrush plains, this chipmunk also ranges into the borders of open forests on the mountain sides. It is most numerous on flats and foothill slopes among heavy growths of sage and rabbit brush. When its territory is invaded by settlers it does not hesitate to gather about the borders of fields and even to raid barns in search of grain and other food. Its burrows are dug under large sagebrush and other bushes and under rocks and similar shelter.