They vary much in numbers from year to year and at times appear to increase suddenly in localities where food is plentiful, indicating a probable food migration. The young, numbering from four to six in a litter, are born at varying times between the last of April and late summer, indicating the possibility of more than one litter a season. The most characteristic note of this chipmunk is a throaty _chuck, chuck_, which is ordinarily used as a call note, but which in spring is uttered many times in rapid succession to express the seasonal feeling of joy and well being, thus taking on the character of a song. Such joyful notes may be heard on every hand in places where the little songsters are numerous. In addition, they have a high-pitched, chirping note and a small churring whistle when much alarmed. =THE OREGON CHIPMUNK= (=Eutamias townsendi= and its relatives) (_For illustration, see page 543_) The resident species of birds and mammals in the humid coastal region of Oregon, Washington, and southern British Columbia are strikingly characterized by their darker and browner colors in comparison with closely related species in more arid districts. 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.