SCATTER-HOARDING BY A LARDER-HOARDING RODENT - INTRASPECIFIC VARIATION IN THE HOARDING BEHAVIOR OF THE EASTERN CHIPMUNK, TAMIAS-STRIATUS

The adaptive significance of alternative patterns of dispersing hoarded food was examined by determining which factors influence the occurrence of scatter-hoarding in the eastern chipmunk a species that typically larder-hoards food to its burrow. A standardized food-provisioning test was used to determine the incidence of scatter-hoarding in relation to age, sex, reproductive condition, time of year, patch position and social context. Juveniles and females with young scatter-hoarded significantly more often than did other classes. Newly emerged juveniles scatter-hoarded both before and after they acquired a permanent burrow of their own, but decreased their frequency of scatter-hoarding as they grew older and more capable of defending their burrow. Females with young in the burrow did not appear to use scatter-hoarding to avoid revealing the location of the burrow, but may have been avoiding the risk that their young would consume all their hoarded food. The incidence of scatter-hoarding was not affected by the distance of the patch from the burrow nor by the number of competing sciurids at the patch. However, scatter-hoarding was more often performed by individuals that were harassed at the patch. This may have been a response to leaving the patch with an incomplete load; experimental exclusion of animals before they had completed loading demonstrated that possessing a small load increased the tendency to scatter-hoard. For juveniles and non-breeding adults, scatter-hoarding permitted more rapid removal of food from a patch than did larder-hoarding, but for females with young, scatter-hoarding trips took longer than larder-hoarding would have, largely because such females often made more than one hoard per trip. These results do not support the hypotheses that scatter-hoarding is a vestigial behaviour pattern of no adaptive significance or that is is simply a response to lack of larder space. They do, however, support the hypotheses that scatter-hoarding reduces pilferage of hoarded food by individuals unable to defend a larder and that it increases the rate at which subordinate individuals can sequester food from ephemeral patches.