Memory for food caches: not just for retrieval

Many animals use hoarding as a long-term strategy to ensure a food supply at times of shortage. Hoarders employ strategies that enhance their ability to relocate caches such as remembering where caches are located. Long-term scatterhoarders, whose caches have potentially high pilferage rates, should also hoard in a way to reduce potential cache pilferers' ability to find caches. Previous studies have demonstrated that this could be achieved by hyperdispersing caches to reduce the foraging efficiency of pilferers. This study investigates whether coal tits (Parus ater) indeed place their caches away from existing ones. In our experiment, birds hoarded food in 3 conditions: when caches from a previous storage session were still present, when caches from a previous storage session were not present anymore because the bird had retrieved them, and when caches from a previous storage session had been removed by the experimenter. We show that coal tits hoard away from existing caches and that they do not use cues from extant caches to do this. This evidence is consistent with the use of memory for the locations of previous caches when deciding where to place new caches. This finding has important implications for our understanding of the selective pressures that have shaped spatial memory in food-hoarding birds.