How squirrels protect their caches: Location, conspicuousness during caching, and proximity to kin influence cache lifespan

Abstract

Scatter-hoarding animals cannot physically protect individual caches, and instead utilize several behavioral strategies that are hypothesized to offer protection for caches. We validated the use of physically altered, cacheable food items, and determined that intraspecific pilfering among free-ranging fox squirrels (N = 23) could be assessed in the field. In this study we were able to identify specific individual squirrels who pilfered or moved caches that had been stored by a conspecific. We identified a high level of pilfering (25%) among this population. In a subsequent study, we assessed the fate of squirrel-made caches. Nineteen fox squirrels cached 294 hazelnuts with passive integrated transponder tags implanted in them. Variables collected included assessment and cache investment and protection behaviors; cache location, substrate, and conspicuousness of each cache; how long each cache remained in its original location, and the location where the cache was finally consumed. We also examined whether assessment or cache protection behaviors were related to the outcomes of buried nuts. Finally, we measured the population dynamics and heterogeneity of squirrels in this study, testing the hypothesis that cache proximity and pilferage tolerance could serve as a form of kin selection. Polymer chain reaction (PCR) was used to analyze hair samples and determine relatedness among 15 squirrels, and the potential impact of relatedness on caching behavior. Results suggested that cache protection behaviors and the lifespan of a cache were dependent on the conspicuousness of a cache. Squirrels may mitigate some of the costs of pilfering by caching closer to the caches of related squirrels than to those of non-related squirrels.