The function of song overlapping in hermit thrush (Catharus guttatus)

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University of New Brunswick


Male songbirds may mediate aggressive competition by singing concurrently with their rival, termed song overlapping. Support and criticism for overlapping functioning as an aggressive signal exist; many species adjust their singing to avoid sound interference, including during male competition. In this study, natural rates of overlapping were measured using past recordings of hermit thrush. Playback studies were used to examine overlapping in a male-male aggressive context versus in response to different bird species’ songs. No association was found between overlapping and physical aggression. The conspecific playback and counter-singing groups showed similar degrees of overlapping avoidance, with birds that were exposed to the heterospecific playbacks showing the least amount. These results suggest that overlapping is not an aggressive signal in this species and may occur for other reasons, such as avoiding acoustic interference. This study expands on the understanding of how aggressive signaling and acoustic interference affect patterns of birdsong. Keywords: hermit thrush, acoustic interference avoidance, song overlapping, playback, aggression