The rationality of animal memory : Complex caching strategies of western scrub

Scrub cache perishable and non-perishable foods, and their caches may be pilfered by conspecifics. Caching and recovery by scrub-jays is psychologically rational in the sense that these behaviours responded appropriately to conditions that should have changed the birds’ beliefs and desires. For example, scrub-jays were allowed to cache worms and peanuts in a visuo-spatially distinct tray. At recovery, birds search initially for worms after a short retention interval because they believe that the worms are still edible, but switch to searching for peanuts at a long retention interval because they believe that worms are now degraded. If jays acquire new information after caching, such that worms are no longer edible when recovered at the short interval, this should affect their belief about the state of their caches. Jays update their cache memory, and on subsequent trials of the short interval, search selectively in peanut sites. In a second example, scrub-jays cached either in private (when another bird's view was obscured) or while a conspecific was watching, and then recovered their caches in private. Scrub jays with prior experience of stealing another bird's caches subsequently recached food in new sites during recovery trials, but only when they had been observed caching. Naïve birds did not. We suggest that experienced pilferers had formed a belief that observers will pilfer caches they have seen, and re-