Figure 5

Predicted values of the “call with mother” (frequency of occurrence), i.e. production of female-like great calls by young males in co-singing interactions with their mothers plotted against the log-transformed age (months) of young males. Values for each cases are categorized according to the following forms of the multi-modulation phrase: Fm0-1—a non-mature form of the multi-modulation phrase, which contains one or no frequency modulation in the second note of the multi-modulation phrase; and Fm2—a mature form of the multi-modulation phrase, which contains two or more frequency modulations in the second note of the multi-modulation phrase.