We captured least chipmunks (Tamias minimus) and eastern chipmunks (T. striatus) from overlapping populations and assessed their comparative success at heterospecific pilfering in a naturalistic laboratory setting. The smaller species (T. minimus) found their competitors' caches more quickly and with less effort. We traced the success of least chipmunks to foraging behavior that targeted the vulnerabilities of eastern chipmunk caches, and a cache placement counterstrategy that protected their own food stores. The value of pilfered caches for least chipmunks was magnified by their smaller body size and the bigger cache size of their larger competitor. We suggest that heterospecific cache pilferage represents an especially lucrative foraging tactic for small foragers.

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