How Nutcrackers Find Their Seed Stores

The Clark's Nutcracker (Nucifraga columbiana) stores conifer seeds in the late summer and fall of each year. During winter and spring, seeds from buried caches are the major food of nutcrackers and their young. A bird must find more than a thousand seed caches each year. The alternative means by which nutcrackers may locate seed stores are (1) memory of cache site and (2) trial and error search. While searching for stored seeds, a Clark's Nutcracker makes a series of prod holes with its bill. A hole from which a cache was recovered is usually distinguished by a pile of broken seed coats. This allows an estimate of a nutcracker's success rate in locating seed caches. Theft of seed caches by rodents and removal of intact seeds from cache sites by nutcrackers may confuse this estimate. A field technique based on deductive reasoning is presented to determine how nutcrackers recover their caches. In the eastern Sierra Nevada I gathered field data on the success rate and nearest neighbor distances among prod holes in spring and summer of 1975. Data indicating the proportion of caches taken by rodents were obtained in 1978. Analyses of these data suggest that nutcrackers find most of their caches by means of memory. A search based on memory implies that seed stores are not communal and that nutcrackers must remain in the area where they stored seeds until the following summer. Theft of seed stores by rodents must be an important selective pressure on nutcracker caching behavior. By caching seeds in storage areas which become covered with deep snow, nutcrackers may reduce their losses to rodents.