Pilfering Eurasian jays use visual and acoustic information to locate caches.

Pilfering corvids use observational spatial memory to accurately locate caches that they have seen another individual make. Accordingly, many corvid cache-protection strategies limit the transfer of visual information to potential thieves. Eurasian jays (Garrulus glandarius) employ strategies that reduce the amount of visual and auditory information that is available to competitors. Here, we test whether or not the jays recall and use both visual and auditory information when pilfering other birds' caches. When jays had no visual or acoustic information about cache locations, the proportion of available caches that they found did not differ from the proportion expected if jays were searching at random. By contrast, after observing and listening to a conspecific caching in gravel or sand, jays located a greater proportion of caches, searched more frequently in the correct substrate type and searched in fewer empty locations to find the first cache than expected. After only listening to caching in gravel and sand, jays also found a larger proportion of caches and searched in the substrate type where they had heard caching take place more frequently than expected. These experiments demonstrate that Eurasian jays possess observational spatial memory and indicate that pilfering jays may gain information about cache location merely by listening to caching. This is the first evidence that a corvid may use recalled acoustic information to locate and pilfer caches.