Quantitative acoustic analysis of the vocal repertoire of the crowned lemur

Abstract

Only a preliminary qualitative description of the vocal repertoire of Eulemur coronatus is available and no quantitative study of the calls of any wild or captive crowned lemur has ever been performed. The aim of this study was to verify whether the categories of calls in the crowned lemur's vocal repertoire briefly described on qualitatively bases by Macedonia & Stanger (1994) correspond to discrete phonetic categories. Through all-occurrence and focal animal observations, we recorded the vocal activity of 37 crowned lemurs housed in five institutions, both in Europe and Madagascar. We measured both temporal and spectral properties to describe calls quantitatively. We extracted acoustic parameters in the perspective of the source-filter theory of sound production. From spectrograms, we measured call duration and 6 larynx-related features and, using Linear Predictive Coding spectra, we measured four vocal tract related acoustic properties. From a preliminary qualitative inspection of the spectrograms, we identified the 12 types of vocalizations previously described by Macedonia & Stanger (1994) and partially by Petter & Charles-Dominique (1979). Our quantitative analysis has statistical support for a clear classification of 10 acoustic types: Long Grunt, Long Grunt Clear Call, Grunted Hoot, Grunt, Snort, Click, Hoot, Alarm Call, Tonal Call and Scream. In particular, cross-validated Discriminant Function Analysis successfully classified a high percentage of the vocal signals in the 10 vocal categories. Acoustic cues of both larynx-related and vocal tract-related acoustic parameters also offered preliminary support for both sex and individual identity potential that should be more thoroughly investigated in future studies.