Social complexity can drive vocal complexity: Group size and information in chickadee calls in Carolina chickadees

Abstract

There is considerable variation in systems of vocal communication in animals. One hypothesis to explain this variation is that the complexity of the social group influences the groups vocal complexity. This social complexity hypothesis for communication is also central to recent arguments for human language origins, but experimental tests of the hypothesis are lacking. This study investigated whether group size, a fundamental component of social complexity, influenced the complexity of the chickadee call, a call system functioning in social organization of Carolina chickadees, Poecile carolinensis. This call system has been studied in chickadees and related species, and is structurally and functionally rich in its note composition. Complexity of calls was measured using uncertainty (diversity) related to note composition, based on Shannon’s mathematical theory of communication. In unmanipulated field settings, calls of individuals in larger groups had greater complexity (more information) than calls of individuals in smaller groups. In aviary settings manipulating group size, individuals in larger groups used calls with greater complexity than individuals in smaller groups. These results indicate that social complexity can influence communicative complexity in this species.