Linking summer foraging to winter survival in yellow pine chipmunks (Tamias amoenus)

Abstract

This study links summer foraging and scatter-hoarding to winter larder-hoarding and winter survival in yellow pine chipmunks (Tamias amoenus) by comparing patterns of time allocation and winter larder contents in 2 years with very different levels of resource availability. In 2003, seed production and the number of trees and shrubs producing seeds were high. In 2004 seed crops were small. Chipmunks allocated more time to foraging when food resources were scarce (66% in 2004) compared to when they were abundant (39% in 2003). Increased time allocated to foraging in 2004 corresponded to significant decreases in time allocated to vigilance, resting, and social interactions. When seeds were scarce (i.e., in autumn 2004), chipmunks spent more time searching for cached food items than gathering seeds from plants or the ground surface. Despite the increase in foraging effort, the edible mass and caloric contents of larders were significantly smaller in 2004. In the year with low seed production, the diversity of seed species found in larders increased, and many of these seeds were of species that ripened in summer. When autumnal seed production by Jeffrey pine seeds was high, Jeffrey pine seeds were nearly the exclusive food item found in larders. Larder contents would have provisioned chipmunks for an estimated 116–257 days in 2003 and but only 6–111 days in 2004. It is likely that all chipmunks would have survived the winter of 2003 (duration ~110–120 days). However, none of the larders recovered in 2004 contained enough food to have provisioned the inhabitant for the ~148–158 days of winter.