Joanna M. Dally

Cache protection strategies by western scrub–jays (Aphelocoma californica): hiding food in the shade

In the presence of conspecifics, food–caching western scrub–jays (Aphelocoma californica) implement a variety of strategies to reduce the chances of cache theft. This experiment aimed to determine whether the jays could exploit an environmental variable, the level of ambient light, to reduce the transfer of visual information to potential pilferers. Each jay was allowed to cache non–degradable food in two trays, one of which was well lit, whereas the other was in shadow. In some trials the birds cached in private and in others they were observed; however, they always recovered their caches in private. When observed the jays preferentially cached in the shaded tray, whereas both trays were used equally when caching in private. By caching in shaded sites, the quality and transfer of visual information available to the observer may be reduced, thereby making the location of cache sites less certain. These results suggest that western scrub–jays may selectively cache in the shade as a strategy to reduce the chance of cache theft by observing conspecifics.

Food caching by western scrub-jays (Aphelocoma californica) is sensitive to the conditions at recovery.

Western scrub-jays (Aphelocoma californica) cached perishable and nonperishable food items, which they could recover after both short and long retention intervals. When perishable items were always degraded at recovery, jays decreased the number of perishable items cached and increased their caching of nonperishable items, relative to a control group whose caches were always fresh at recovery. Jays reduced the number of nonperishable items cached, however, when highly preferred food items were degraded only after the long retention intervals. The findings are discussed in terms of the role of retrospective and prospective processes in the control of caching.

The social suppression of caching in western scrub-jays (Aphelocoma californica)

This study focussed on the social suppression of caching in 3 groups of western scrub-jays (Aphelocoma californica). Each group (3 males and 4 females) were housed in a separate aviary. Only the dominant male and/or his partner cached in each aviary. When the alpha pair was removed from the aviary, however, caching by the beta pair increased significantly. As all subordinate birds cache when housed individually, cache cessation was attributed to social suppression. In each aviary, storers from both the alpha and beta pairs tolerated their partners recovering their caches, but treated all other birds aggressively if they approached a cache site. The storer and their partner tended to move one anothers caches around multiple times, possibly making the final location of caches ambiguous. Importantly, caches were only moved around repeatedly on trials where multiple pilfering attempts were made. Western scrub-jays therefore appear to adjust their caching behaviour depending on the risk that observers pose to their caches.

Don't call me birdbrained

Spying and stealing are all in a days work for some members of the crow family. Could that explain why they are so clever, asks Joanna Dally