Finding Hidden Caches
photograph of an Oak Titmouse by Tom Grey
does a long-term hoarder like Clark's Nutcracker recover
stored seeds when it needs them to feed its young?
Ornithologists at first thought that the food was stored
only in certain kinds of areas, and that the birds
rediscovered it by later foraging in the same areas. But
recent experiments with nutcrackers in aviaries, done by
Stephen Vander Wall of Utah State University, have shown
clearly that individuals are able to recall where they have
cached seeds. The birds remember where the seeds are in
relation to certain landmarks, such as rocks. If the
landmarks are moved, the areas the birds search are
displaced an equivalent amount.
The results of theseexperiments confirmed observations by behaviorist Diana Tomback, who
examined the distribution of beak marks in earth and snow where nutcrackers had searched for caches. The marks were not random, but rather unsuccessful probes were clustered in the vicinity of successful ones (indicated by the presence of pinyon-seed coats, which the birds removed before eating the seeds, next to the hole). In addition, early in the year before rodents started to find the caches, the birds found caches on about two out of three attempts, far more frequently than one would expect if they were searching at random. This capacity to remember the sites of stored food seems to be an evolutionary enhancement of a spatial memory that is more widespread in birds. For example, titmice often store food in diverse places when it is abundant. They show excellent short-term (hours-days) memory for the storage locations, as elegant experiments by British avian behaviorist John Krebs and his colleagues have shown.
Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.