Ecology: Magpies living in bigger groups are no bird brains

Australian magpies living in larger groups show increased cognitive performance, which, in turn, is linked to increased reproductive success, according to a study published online in Nature this week. The results suggest that the social environment has a major role in driving both the development and evolution of cognitive traits.

In species living in stable social groups, within-population variation in group size could generate differences in information-processing demands, which may influence cognitive traits. Previous research has shown that measures of brain structure are linked with group size in humans, captive cichlid fish and captive macaques, but the relationship between group size and cognition in wild animals is unknown.

Benjamin Ashton and colleagues examined whether group size predicts individual cognitive performance within a population of wild Australian magpies. The authors quantified individual cognitive performance in 56 birds from 14 groups, ranging in size from 3 to 12 individuals, using four different tasks designed to measure processes including spatial memory. They found that group size was the strongest predictor of adult performance across all four tasks, with individuals from larger groups outperforming those from smaller groups. The relationship between group size and cognition emerged in early life (200 days post-fledging).Furthermore, the authors found a positive link between the performance of female magpies in the tasks and three indicators of reproductive success. Therefore, the authors suggest that reproductive success could be a selective benefit of greater cognitive performance.