The influence of environmental conditions on cache recovery and cache pilferage by yellow pine chipmunks (Tamias amoenus) and deer mice (Peromyscus maniculatus)

Abstract

I conducted a field experiment in 10 x 10 m enclosures to explore how seed and soil moisture levels influence the ability of knowledgeable and naive rodents to find natural caches of Jeffrey pine (Pinus jeffreyi) seeds. Subjects were yellow pine chipmunks (Tamias amoenus) and deer mice (Peromyscus maniculatus) searching for caches that they had made, caches made by other individuals of the same species, or caches made by individuals of the other species. Subjects that made caches (knowledgeable subjects) relied on spatial memory to find many of their own caches during recovery sessions, and their ability to locate caches was not affected by water content of seeds or soil. Naive subjects found few caches under dry conditions, but under wet conditions, they located as many caches as did the rodents that made them. Naive subjects apparently relied on olfaction to find caches, a sensory modality that works more effectively under moist conditions. Subjects had as much success foraging for caches made by members of their own species as for caches made by the other species. I present a hypothesis that predicts how foragers could modify predominately memory-based search to predominately olfactory-based search as the weather changes from dry to wet. When foragers rely on spatial memory, those foragers find only their own caches, but when they can also use olfaction, they pilfer caches made by other individuals. Consequently, the nature of competitive interactions among members of the seed-caching guild may change as the weather changes.