DOES OVERLAPPING CHANGE BETWEEN INDRIS SONGS EMITTED IN DIFFERENT CONTEXTS?

The “singing” primates are often compared to the singing behavior of some tropical birds, which establish monogamous couples, live in forest environments and perform duets or choruses. In some bird species there is evidence that the degree of overlap between songs of different individuals may change in relationship with specific factors (e.g. neighbor-stranger discrimination, aggressiveness). In Indri indri, males and females within a social group emit loud, long distance calls in a coordinated manner. An indri may start emitting a vocal utterance before the end of another individual’s contribution, resulting in different degrees of overlap between individual songs. This study provides the first quantitative analysis of the overlap between individual contributions in the indris’ song. We analyzed 52 songs emitted in 3 different contexts (advertisement, territorial, cohesion). We found that overlap is present in the song given in all contexts we examined. The total duration of the song, the ratio between voiced and unvoiced portions, the ratio between the total overlap and the total duration of the song, and the ratio between unvoiced parts and the total overlap showed significantly differed across context (p < .05). These results suggest that characteristics of different songs can transmit context-specific cues to conspecifics.