Acorn Pericarp Removal as a Cache Management Strategy of the Siberian Chipmunk, Tamias sibiricus

Numerous recent studies have revealed a variety of behavioral adaptations of rodents for maximizing returns from cached seeds. Herein we report on a novel behavior by the Siberian chipmunk (Tamias sibiricus) in northeastern China, by which they consistently remove the pericarp (shell) of Quercus mongolica acorns before dispersing and caching these nuts. We investigated the effects of pericarp removal on acorn germination, tannin concentrations, cache pilferage, and insect damage, to determine if and how pericarp removal facilitates cache management by Siberian chipmunks and whether or not such behavior influences seed fates. Chipmunks cached acorns only after the pericarps were removed. Chipmunks preferred pericarp-removed acorns over intact acorns when removing them from seed stations for both consumption and caching. Pericarp removal did not affect germination or tannin concentration of cached Q.mongolica acorns, suggesting that the behavior is not an adaptation for long-term storage and tannin decomposition. Acetone treatments of the pericarp and artificial pericarp removal failed to alter pilferage rates by Siberian chipmunks and wood mice (Apodemus peninsulae). Since damage of acorns by weevils often leads to cache losses, we also tested the effects of weevil infestation on cache decision following pericarp removal. Siberian chipmunks removed pericarps and then scatter hoarded significantly more sound than weevil-infested acorns, strongly suggesting that pericarp removal is used to discriminate between the infested and non-infested acorns. Thus, we argue that the primary function of this behavior is to ensure successful storage of sound acorns, at least for short-term storage. Future studies should consider the potential impact of pericarp removal on weevil populations and long-term patterns of seed survival and establishment from the Siberian chipmunk ' s caches.