The energetics of autumn mast hoarding in eastern chipmunks.

The timing and basis of the transition from energy reserve accumulation to reserve utilization in autumn may be a key determinant of winter survival in endotherms, but has rarely been examined directly in the field. In the present study we quantify the energetics of autumn mast hoarding in eastern chipmunks (Tamias striatus) to document the degree to which larder hoarding permits capitalizing on brief pulses of resource abundance and to evaluate the basis of the decision to stop hoarding and initiate hibernation. Daily energy expenditure, measured with the doubly labeled water technique, increased significantly with date and decreasing ambient temperature, eventually exceeding 3× resting metabolic rate in late autumn.