Clark's nutcrackers Nucifraga columbiana remember the size of their cachedseeds

Clark's nutcrackers (Nucifraga columbiana) hide thousands of seeds in subte rranean caches that they later recover using spatial information about cach e location. In two experiments, we tested whether nutcrackers also remember another type of information regarding their caches - the size of the seeds in each cache. We videotaped birds during cache recovery and then measured their bill gape during probing behaviour as captured on the videotape. In experiment one, six birds each experienced two treatments: one that allowed them to cache and then recover large seeds, and the other, an identical tr eatment using small seeds. During this experiment, all six birds used a wid er gape when attempting to recover seeds during the large-seed treatment th an during the small-seed treatment, and gape width was significantly correl ated with seed size. During experiment two, we presented birds with both la rge and small seeds within the same caching session. We also increased the retention interval between caching and recovery. These modifications increa sed the difficulty of the task. Six of the seven birds used a wider gape du ring seed recovery when digging for caches that contained large seeds than they did when searching for small seeds. The ability to remember the size o f seeds placed within caches may serve to increase the likelihood of speedy and successful recovery. It also allows the birds another level of organiz ation of their food supply. These are the first experiments to suggest that Clark's nutcrackers remember more about their caches than location alone.