| Young male Sonoma chipmunks disperse from the nest after weaning, but females remain near where they were born. From December through June, males travel extensively, seeking mates and competing with other males. Because of this, they are more exposed to predators than females. About equal numbers of male and female young emerge from the nest, but more females than males survive their first winter. Apparently a number of females do not survive their first attempt at reproduction, however, because by fall the number of yearling males and females in a population is about equal. On average, females live longer: by the time they are 3-5 years old there are more females than males. These chipmunks commonly occur in low, dry forests of ponderosa pine, and in chaparral and open areas of redwood forests.
Grinnell, J., 1915. Eutamias sonomae, a new chipmunk from the inner northern coast belt of California, p. 321. University of California Publications in Zoology, 12:321-325.
Mammal Species of the World
Mammalian Species, American Society of Mammalogists' species account