VOCAL CUES TO BODY SIZE AND INDIVIDUALITY IN LEMURS

The source–filter theory has been successfully applied to the study of animal vocal signals since the 1990s. As an extension, models reproducing vocal tract resonance can be used to reproduce formant patterns and to understand the role of vocal tract filtering in non-human vocalizations. We investigated the acoustic structure of grunt vocalizations in red-bellied lemurs (Eulemur rubriventer) and we found a potential for individual discrimination. Formants were effective in assigning 80.5% of the vocalizations to the correct emitter. We then built a computational model of the red-bellied lemur nasal tract using morphological measurements and we estimated how the characteristics of the vocal tract might underlie individual-specific formant patterns. We found that individual-level variation is strongly related with the morphology of nasal cavities and that length of the tract potentially provides the most important cue to body size.