Flexible use of memory by food-caching birds

Animals use memory-guided and memory-independent strategies to make
navigational decisions. Disentangling the contribution of these strategies
to navigation is critical for understanding how memory influences
behavioral output. To address this issue, we studied spatial behaviors of
the chickadee, a food-caching bird. Chickadees hide food in concealed,
scattered locations and retrieve their caches later in time. We designed
an apparatus that allows birds to cache and retrieve food at many sites
while navigating in a laboratory arena. This apparatus enabled automated
tracking of behavioral variables – including caches, retrievals, and
investigations of different sites. We built probabilistic models to fit
these behavioral data using a combination of mnemonic and non-mnemonic
factors. We found that chickadees use some navigational strategies that
are independent of cache memories, including opportunistic foraging and
spatial biases. They combine these strategies with spatially precise
memories of which sites contain caches and which sites they have
previously checked. A single memory of site contents is used in a
context-dependent manner: during caching chickadees avoid sites ­that
contain food, while during retrieval they instead preferentially access
occupied sites. Our approach is a powerful way to investigate navigational
decisions in a natural behavior, including flexible contributions of
memory to these decisions.