Sex dimorphic phrase combinatorics in the song of the indris (Indri indri)

We used a logic distance to investigate intra and inter-individual variation in the phrase combinatorics of a singing primate, the indri, which inhabits the montane rain forests of Madagascar. Indris combine long notes, short single notes, and phrases consisting of two, three, four, or five units with slightly descending frequency. We calculated the similarity across different individual songs using the Levenshtein distance. We then analyzed the degree of similarity within and between individuals and found that: i) the phrase structure of songs varied between reproductive males and females; ii) male contributions to the song are overall more similar to those of other males; iii) male contributions are more stereotyped than females' ones. The picture emerging from phrase combinatorics in the indris is in agreement with previous findings of rhythmic features and repertoire size, which also suggested that female songs are potentially more distinctive than those of males.