Figure 2. Oscillogram (top panel), spectrogram (middle panel) and subsyringeal air sac pressure (bottom panel) of a male (A, before nerve cut, C, same individual after nervecut) and a female (B, before nerve cut, D, same individual after nervecut) distance call as well as of two representative examples of respiratory sounds (E).

The two arrows in A indicate a high (1) fundamental frequency at the beginning of the male call and a low (2) fundamental frequency in the middle and end of a male distance call. This frequency modulation does not occur in females and was also missing in one of the three males in this study. Calls in A and B are representative before nervecut surgery, and C and D are examples from the same individuals after tracheosyringeal nervecut.