Repertoire size and composition in great tits: a flexibility test using playbacks

Abstract

In many bird species, song repertoire characteristics play an important role in intersexual competition and intrasexual attraction. Studies on the importance of having a large repertoire typically assume the available song types as a fixed trait. However, repertoire composition may be flexible. We explored the effects of playbacks on the composition and use of the song type repertoire in great tits, Parus major . Playbacks simulate a nearby competitor male, vocally advertising territoriality. We compared the effects of novel song types with two control groups, one in which we played back one of the song types from the repertoire of the focal individual, and one without playback. The repertoire size for individual great tits of actively used song types remained more or less constant, but playbacks led to a significant turnover in repertoire composition over a relatively short period (about a week). The repertoire assessment across three experimental phases led to significantly larger accumulated repertoires compared to the more traditional short-term assessment method. The appearance of new song types was especially prominent among birds treated with a novel song type, suggesting the process is socially mediated. None of the ‘new’ song types were accurate copies of the novel unfamiliar song types played back. We discuss the potential origin of these ‘new’ song types and the impact of repertoire plasticity on signal value for sexual selection.