The vocal communication of the mongoose lemur (Eulemur mongoz): phonation mechanisms, acoustic features and quantitative analysis

Abstract

We recorded vocalisations of wild Eulemur mongoz groups in Madagascar and the Comoros Islands, as well as from habituated captive groups housed in European and Madagascan zoos. Each vocalisation was quantitatively described by means of an acoustic analysis procedure implemented in Praat, and vocal types were distinguished both by ear and by the visual screening of spectrograms. Vocal signals were then associated with the context in which they were produced, to explore whether they occur only in specific behavioural contexts or are uttered in a range of situations. We found that mongoose lemurs possess highly context-specific aerial alarm calls and territorial calls, while the 'croui-croui' is usually emitted to communicate between individuals regrouping at sunset. The other calls we recorded, such as those including low-pitched pulse trains sometimes followed by harmonic elements, were not tightly associated with a particular context. Mongoose lemur utterances included calls produced with closed mouths and the involvement of nasal resonance, or with constant degrees of mouth opening or mandible 'articulation' during phonation. We observed 15 vocal types, nine of which were entered into a multivariate model that classified vocal types with a high degree of reliability. The second and third formants played an important role in discriminating among types of calls.

Clarifying and expanding the social complexity hypothesis for communicative complexity

“…This bias, together with the diversity of quantitative methods applied to identify call types, currently results in substantial inhomogeneity among studies. For example, the vocal repertoire of the Mongoose lemur (Eulemur mongoz) has been characterized by visual inspection as composed of either 8 (Petter and Charles-Dominique 1979), 10 (Curtis and Zaramody 1999), or 14 (Gamba et al 2015) call types, whereas quantitative analyses suggested 9 (Gamba et al 2015) or 15 (Nadhurou et al 2015) different call types. Thus, there is currently no general agreement on how to identify different call types and, hence, how to assess vocal repertoire size objectively.…”

The postnatal ontogeny of the sexually dimorphic vocal apparatus in goitred gazelles (Gazella subgutturosa)

“…An alternative way of lowering call formants, aside from descending the larynx, is shifting from oral to nasal call emission, as nasal vts are longer than oral vts, not only in trunk-nosed mammals (saiga antelopes (Saiga tatarica): Frey et al, 2007; African elephants (Loxodonta africana): Stoeger et al, 2012) but also in species with typical nose sizes (goitred gazelles: Efremova et al, 2011a;Volodin et al, 2011; mongoose lemurs (Eulemur mongoz): Nadhurou et al, 2015).…”

Modeling individual vocal differences in group-living lemurs using vocal tract morphology

“…Depending on the acoustic characteristics of the click grunt, we used a window length of 0.025–0.055 s. We detected five to six formants in the frequency range 0–8,500 Hz while searching for 5.5 formants (for details, see Gamba and Giacoma 2007 ). Frequency spectra were then superimposed on the signal spectrogram to verify the goodness of the LPC analysis ( Nadhurou et al 2016 ). A custom-built script was used to automate file opening and saving of the measurements.…”