Cache protection strategies by western scrub-jays, Aphelocoma californica: implications for social cognition

Food-caching western scrub-jays cache items themselves, and use observational spatial memory to steal the caches of others. Our aim in this study was to investigate the strategies used by scrub-jays to reduce cache theft by conspecifics. In three experiments, scrub-jays were allowed to cache wax worms in two different locations. In experiment 1, the birds preferred to hide items in distant sites when watched by another jay, but used near and distant sites equally when the observer's view was obscured by a screen. As conspecifics rely on observational spatial memory to steal other jays' caches, this use of distance might reduce the visual information available to the potential thief and thus decrease pilfering accuracy. Where possible, however, placing caches out of sight may be more effective. In experiment 2, storers cached predominantly in distant, out-of-view, sites. However, items placed in view of the observer were moved multiple times, possibly confusing the observer as to their location. In experiment 3, when in-view and out-of-view sites were equidistant to the observer, storers cached mainly in out-of-view sites when observed, but cached equally in both sites when not observed. In all three experiments, some items were cached in nonpreferred sites (near, in view). During recovery sessions, when the storer was not observed, these items were selectively recached in new sites unbeknown to the observer. It may be advantageous not to hide all the caches in one place, because unpredictability might provide the best insurance against pilfering.