Annual Cycle of Cliff Chipmunks in the Santa Catalina Mountains, Arizona

Abstract

Field data on seasonal activity, body weights, molt, and reproduction were collected during a 15-month trap-release study of cliff chipmunks, Eutamias dorsalis, in a pine-oak forest in the Santa Catalina Mountains of southeastern Arizona. Males were active throughout the year with a lull in late December and January, but females disappeared completely from late December through February and did not fully resume activity until late April. Neither sex appeared to gain weight before the period of winter inactivity, and their weights were lowest following this period. Females were consistently heavier than males among both adults and juveniles. Adult females molted to summer pelage mainly during June and July, about one month later than adult males. This delay may reflect the energetic burden of breeding for females, but some females were actively molting while pregnant and lactating. Males were reproductively active from January through June, but the actual breeding season varied between the two summers studied. In 1970 most females copulated in late May and their young did not appear above ground until early August, but in 1971 females started to copulate in April and young chipmunks first appeared in late June. The lateness of the 1970 season may have been due to an unusually cold spring. During both years some females appeared to have copulated well after the majority, which produced an extended breeding season. There were no records of females having more than one litter per year. Although almost all adult females bred during 1970, a large proportion apparently did not breed during 1971, perhaps owing to the severe winter-spring drought of 1970 to 1971. The breeding season of cliff chipmunks in Arizona and New Mexico has a wider seasonal spread than for other species of Eutamias, possibly because of both winter and late summer precipitation and fairly mild, short winters. Food availability seems to be low in southern Arizona during the hot dry season (April to June) and greatest during the late summer rains (July to September), yet cliff chipmunks breed during the hot dry season as do most species of birds and mammals in this area. This observation contrasts with the prediction that vertebrates should attempt to raise offspring when food is most available.