The Effects of Seed Value on the Caching Behavior of Yellow Pine Chipmunks

Abstract

Yellow pine chipmunks scatter-hoard a variety of seed types, and these seeds vary considerably in their inherent value to the chipmunks. Models of optimal scatter hoarding behavior predict that animals should space items of greater value farther apart than items of lesser value to discourage theft from cache robbers. This prediction was tested by comparing how yellow pine chipmunks Tamias amoenus distribute Jeffrey pine Pinus jeffreyi and antelope bitterbrush Purshia tridentata seeds to cache sites. Chipmunks prefer Jeffrey pine seeds over bitterbrush seeds ; the pine seeds provide energy 3.8 times faster and contain a higher proportion of fat than bitterbrush seeds. The prediction of the model was upheld on several counts : chipmunks carry Jeffrey pine seeds farther from source plants to cache sites, they space Jeffrey pine seed caches farther apart, and they place fewer Jeffrey pine seeds than bitterbrush seeds in individual caches. Yellow pine chipmunks appear to be sensitive to the qualities of the food items they store and modify their caching behavior to reduce loss of more valuable food items.