Sex Differences in The Song of Indri indri

In some primate species, males and females within a social group emit loud calls in a coordinated manner or chorus. Indri indri emits a very conspicuous loud call which elicits the loud calls of neighbouring groups. Previous investigations have hypothesised that the main functions of the indri chorus are related to territorial announcement, intergroup avoidance and group cohesion. We investigated sex differences in indri song. We recorded and analysed songs given by 10 different groups, over 160 days. Overall singing duration did not vary between the sexes. However, males emitted significantly fewer but longer notes. Adult males and females of each group participated in the song with sex specific repertoires. Females had a song repertoire of eight note types; males shared all their six notes with females. Apart from the initial roars, in all note types shared by both sexes, male notes were significantly longer than female ones, while variations in frequency parameters differed according to the note type. These findings suggest that indri song may provide cues to conspecifics, such as group size and sex composition, which could influence interactions between groups.