Viviana Sorrentino

A quantitative description of the vocal types emitted in the indri's song

The indri’s song is composed of a series of roars uttered simultaneously by several members of a group, followed by a long modulated howl. The latter part consists of overlapping or successive notes emitted by different individuals. Previous qualitative studies have described four different kinds of notes. We provide the first quantitative acoustic investigation of the indri’s song repertoire. After visual inspection of fundamental frequency (F0) modulation and duration in 30 songs and 1995 notes emitted by 30 individuals, we distinguished nine different unit types (roar + 8 modulated units). For these nine putative types, we measured six F0-related and three temporal parameters, which were then subjected to multivariate statistical analysis. Both discriminant analyses and cross-validation procedures classified the vocal types correctly with high reliability.