Patterns of food storing by black-capped chickadees suggest a mnemonic hypothesis

There is no general theory of cache dispersal in food-storing animals. The present study of free-ranging black-capped chickadees, Parus atricapillus, was undertaken to determine whether caches were deployed in ways that might reduce the overall memory load required for cache recovery. Birds were studied in natural habitats of New York state’s Hudson Valley during the time of the year when they lived in flocks. Birds were offered sunflower seeds at feeders during the autumn and winter. Storing flights ended usually at short distances from the feeder and tended to cluster around a preferred orientation. This orientation often persisted on subsequent days and overlapped with that of other flock members. The behaviour observed may reflect a compromise between the need to minimize the energy cost for food storing (close to source), to minimize the risk of thievery (scatter-hoarding), and to optimize the memorization of caching sites. One hypothesis offered to explain this behaviour is that cached sites clustered in a particular direction will be remembered with reference to a common set of landmarks, and thus pose less of a memory load than items cached over a broad area using all directions away from a food source.