Occurrence of duet type 5 in tropical boubous in response to playbacks of duet types 1 (pairs 1–3), 2 (pairs 4–8), 6 (pairs 9–13), and 9 (pairs 14–18) . White bars show duration of the period before playback, the playback period, and the period of continuous singing after playback. Shaded bars show duration of the silent period following playback. Numbers and letters indicate the duet types used. V stands for duet type 5. Pairs 5 and 6 stopped duetting prior to the end of the playback period (dashed lines).
Grafe and Bitz BMC Ecology 2004 4:1 doi:10.1186/1472-6785-4-1