Figure 1

Representative spectrograms for a male (A) and a female (B) showing the vocal patterns of southern yellow-cheeked gibbons (adapted from Hradec and colleagues20). In the male spectrogram, the “multi-modulation” phrase is divided into three notes (blue dashed lines). The second note shows the most rapid change in frequency modulation of the steep up-and-down sweeping sound of the “multi-modulation” phrase (red dashed rectangle).