An investigation of quantity discrimination in Clark's nutcrackers (Nucifraga columbiana).

We examined quantity discrimination in the Clark's nutcracker (Nucifraga columbiana), a corvid bird with a strong dependence upon caching and recovering nuts. We presented 2 sets of nuts simultaneously, in 21 different conditions, to see if the nutcrackers could choose the larger of the 2 quantities. The nutcrackers displayed a strong ability to discriminate quantities of nuts. Like other animals tested previously, the nutcrackers' performance decreased as the ratio of the 2 quantities approached 1. Interestingly, at constant distances, the nutcrackers did not have more difficulty with contrasts containing larger quantities. Thus, nutcrackers have a fine sensitivity for discriminating between 2 quantities. We review the relevant literature and explore the possibility that nutcrackers, like some other birds, may have developed a keen ability to discriminate quantities. This ability may have developed as an adaptive specialization to cope with their scatter-hoarding ecology, though the evidence for such a conclusion is mixed.