Figure 1. Waveform (a) and spectrogram (b) of a male bellow.

Spectrogram settings: FFT method; window length 0.05 s; time step = 0.004 s; frequency step = 10 Hz; Gaussian window shape; dynamic range = 35 dB. Male bellows are characterised by an introductory phase that is followed by a continuous series of inhalations and shorter exhalations.