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

I conducted a held experiment in 10 X 10 m enclosures to explore how seed a nd soil moisture levels influence the ability of knowledgeable and naive ro dents to find natural caches of Jeffrey pine (Pinus jeffreyi) seeds. Subjec ts were yellow pine chip munks (Tamias amoenus) and deer mice (Peromyscus m aniculatus) searching for caches that they had made, caches made by ether i ndividuals of the same species, or caches made by individuals of the other species. Subjects that made caches (knowledgeable subjects) relied on spati al memory to find many of their own caches during recovery sessions, and th eir 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 c onditions, they located as many caches as did the rodents that made them. N aive subjects apparently relied on olfaction to find caches, a sensory moda lity that works more effectively under moist conditions. Subjects had as mu ch 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 ol factory-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.