Experimental evidence for low intra-pair cache pilfering rates in European nuthatches

European nuthatches, Sitta europaea, live all year in permanent pair-territories. In winter, hoarded food is an important food source. To measure the rate of cache pilfering within pairs, each member of six pairs was supplied with either white- or dark-shelled sunflower seeds which the birds cached. When each bird had cached some 100-300 seeds, the feeder was removed and the birds were monitored during their normal foraging. For each sunflower seed that the nuthatches retrieved, the colour of the seed and the sex of the retrieving bird were recorded. In all pairs, each member almost exclusively retrieved seeds of the colour it had itself cached, pilfering amounting to less than 5%. As no clear differences in hoarding niches were detected between the sexes, these results suggest that caches were relocated with the aid of memory