VOCAL RECOGNITION AND SOCIAL COGNITION IN THE ACORN WOODPECKER

Abstract

The social intelligence hypothesis states that the social environment is the primary driver of the evolution of advanced cognition, and predicts that species with more complex social interactions will have more highly developed cognitive abilities. While this hypothesis is generally supported, the specific social selection pressures acting on cognitive evolution are less well understood. Acorn woodpeckers (Melanerpes formicivorus) are group-living birds in which alliances with kin and competition with other groups are often critical to fitness, suggesting that their social cognitive abilities may be particularly complex. In this dissertation, I investigated two pillars of social cognition in the acorn woodpecker: individual recognition and triadic awareness, or knowledge about social relationships between other individuals. In Chapter 1, I played back the calls of a current group member, a former group member, and a non-group member to male and female woodpeckers. While there were no clear differences in response among the three treatments, subjects responded more quickly to callers that had died or disappeared than to callers that were still living in the study area, suggesting that they recognize and monitor former group members post-dispersal. In Chapters 2 and 3, I investigated what acorn woodpeckers know about the relationships between members of other groups by playing back overlapping calls to simulate two individuals from outside the subject’s group calling together, a behavior that normally only occurs between social affiliates. In Chapter 2, females responded more quickly to socially anomalous playbacks in which the callers belonged to two different groups compared to socially congruous playbacks in which the callers belonged to a single group, suggesting they recognize social affiliations between members of other groups. In Chapter 3, females also discriminated between a pair of callers that formerly lived together and a pair of callers that never lived together, indicating that they can recognize relationships between individuals that have not lived together for years. These results suggest that social knowledge about members of other groups is particularly important for acorn woodpeckers, and highlight the importance of considering how social selection pressures external to the core social unit may have shaped the evolution of intelligence.