Fig. 1

Spectrographic representation of a pant hoot, with the four phases and their calls. a – an introduction call, b – a build-up call, c – a climax call, d – a let-down call. In this example, the introduction consists of two calls, the build-up of nine calls, the climax of four calls, and the let-down of eight calls. Red lines below “a”, “b”, “c” and “d” represent durations of calls within the four phases