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

Abstract

10Scatter-hoarding animals cannot physically protect individual caches, and instead 11 utilize several behavioral strategies that are hypothesized to offer protection for caches. 12 We validated the use of physically altered, cacheable food items, and determined that 13 intraspecific pilfering among free-ranging fox squirrels (N = 23) could be assessed in the 14 field. In this study we were able to identify specific individual squirrels who pilfered or 15 moved caches that had been stored by a conspecific. We identified a high level of 16 pilfering (25%) among this population. In a subsequent study, we assessed the fate of 17 squirrel-made caches. Nineteen fox squirrels cached 294 hazelnuts with passive 18 integrated transponder tags implanted in them. Variables collected included assessment 19 and cache investment and protection behaviors; cache location, substrate, and 20 conspicuousness of each cache; how long each cache remained in its original location, 21 and the location where the cache was finally consumed. We also examined whether 22 assessment or cache protection behaviors were related to the outcomes of buried nuts. 23 Finally, we measured the population dynamics and heterogeneity of squirrels in this 24 study, testing the hypothesis that cache proximity and pilferage tolerance could serve as a 25 form of kin selection. Polymer chain reaction (PCR) was used to analyze hair samples 26 and determine relatedness among 15 squirrels, and the potential impact of relatedness on 27 caching behavior. Results suggested that cache protection behaviors and the lifespan of a 28 cache were dependent on the conspicuousness of a cache. Squirrels may mitigate some of 29 the costs of pilfering by caching closer to the caches of related squirrels than to those of 30 non-related squirrels.31