Counting on your friends: The role of social environment on quantity discrimination.

Quantity discrimination has been established in a range of species. However, most demonstrations of quantity discrimination control for social factors by testing animals individually. I tested whether sociality affects quantity discrimination in the wild by comparing the performances of the highly social Mexican jay (MJ; Aphelocoma wollweberi) and the territorial Western scrub jay (WJ; Aphelocoma californica). The birds were given a choice between two lines of peanuts that differed in initial quantity ranging from 2 vs 8 to 14 vs 16. Their choices were recorded until all peanuts were eaten or cached. Whereas non-social WJ selected the larger quantity across all the trials significantly more than chance, social MJ selected the larger line only when the difference in the number of peanuts between lines was small. In MJ, individual choice when selecting the large or small quantity was influenced by what line the previous bird had chosen when the difference in lines was large, with followers significantly more likely to select the smaller quantity. WJ were not significantly affected by the choices of other individuals. The only factors that influenced WJ choice were ratio and total differences between the two quantities. These results suggests that in certain scenarios, both species can discriminate between different quantities. However, MJ were greatly influenced by social factors, a previously untested factor, while WJ were only influenced by ratio and total difference between the quantities, consistent with findings in other species. Overall, this study demonstrates the important role of sociality in numerical cognitive performance, a previously overlooked factor.