Substrate type affects caching and pilferage of pine seeds by chipmunks

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The abiotic environment often influences the ways in which animals interact. By affecting the cues associated with buried seeds, the type of substrate used by seed-caching rodents may alter the relative probabilities of cache pilferage and cache retrieval. We predicted that, after a wildfire, the presence of ash would impair rodents' ability to smell pine seeds on the forest floor. In a laboratory experiment, we compared the foraging success, caching frequency, and cache recovery of chipmunks (six Tamias amoenus and six T. quadrimaculatus) in ash versus sand substrates. Initial results supported our hypothesis: chipmunks found only 2.3% of 108 caches of Jeffrey pine (Pinus jeffreyi) seeds that we buried in ash but found 98% of caches in sand. However, chipmunks made as many or more of their own caches in ash compared with sand (48% for T. amoenus, 73% for T. quadrimaculatus.) When foraging for seeds cached in ash by themselves and by other individuals, they found significantly higher proportions of their own caches (62%) than of caches made by others (25%). However, when foraging in sand, they found high proportions both of their own caches and those of others (86 versus 81%). These results suggest that olfaction is less effective in ash than in sand, that spatial memory enables chipmunks to recover their own caches in ash, and that caching in ash may allow animals to avoid pilferage of stored food. As chipmunks are important dispersers of seeds, changes in their foraging patterns or competitive interactions after fire could significantly affect pine regeneration.

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