Flock-mate familiarity affects note composition of chickadee calls

Abstract

Recent theory in animal communication predicts that a group’s communicative complexity is connected to its social complexity. Social complexity has typically been measured using group size as an index, with larger groups thought to be more complex than smaller groups. However, group size alone does not account for other social differences that could influence the diversity of interactions within a group that may influence communication. In this study, we asked if other social factors could influence communicative behavior in groups by testing the influence of group composition in the Carolina chickadees, Poecile carolinensis. We recorded the vocal behavior of four wild-caught captive groups of familiar chickadees (birds caught from the same naturally occurring flock) and four wild-caught captive groups of unfamiliar chickadees (birds caught from all different naturally occurring flocks) and then analyzed vocalizations by assessing the note types birds used in their chickadee calls. Flocks of familiar chickadees used fewer introductory notes, more C notes, and fewer hybrid notes in their calls compared to flocks of unfamiliar chickadees. Communicative complexity, measured by zero- and first-order uncertainty, did not differ between conditions. We conclude that note composition of call, but not call complexity, varies with flock-mate familiarity.