Bioacoustic data of Barbitistes kaltenbachi A oscillogram showing bioacoustics terminology used in our study B, C details of the calling song (sections of 8 seconds) B second male starting in synchrony C second male starting anti-phasic, first male switching to synchrony D male song with extra syllables (red arrows, see text) E difference in starting time between the trigger syllables of two duetting males, always referring to a focal male; different colours indicate different male combinations; intervals in the lines mark duet pauses.