Lemurs may be able to recognise other monkey species from the nasal grunts they make, an Italian study has found.
The monkeys are known to make grunting calls to communicate in dense forests.
Scientists investigating three closely related species found that variations in the shape of their airways were responsible for different calls among the primates.
Researchers say this is the first study to link vocal tract shape to call identification in the animal kingdom.
The study is published in the International Journal of Primatology and employed techniques usually used to analyse human voices to interpret how the lemurs made their calls distinctive.
The team from the University of Torino, Italy studied three related species: the common brown lemur, the red-bellied lemur and the black lemur.
They constructed computer simulations of the effect that resonance in the airways would have on a nasal call, based on measurements taken from frozen specimens.
To test these simulations, they compared them with the noises that living lemurs made when calling through their nose and found them to be sufficiently accurate.
Analysis of the computer models allowed researchers to pick out characteristics of the different sounds made by the three species of lemur, which are part of the same genus and therefore very similar to each other.
The calls were distinguished between one another by their "formants", a term that is usually applied to the vocal tract resonance that makes one human voice sound different from another.
"Formants are the acoustic determinant of many key phonetic distinctions in human languages," said Dr Marco Gamba, lead author of the study.
He explained that formants played a key role in "characterising individual voices" and added that "formants are also key features for recognizing the sex of a human speaker."
The study found that the lemurs' hearing could be expected to pick up the key differences between calls.
"What is very very interesting is that... these differences allow recognition of species within the same genus," said Dr Gamba.
He explained that, as in humans, the length of the lemurs' airways was a "major determinant" of changes in their calls.
"But, at least for nasal sounds, shape of the vocal tract is also extremely important," he added.
Dr Gamba now hopes that the technique the team used will be applied to analyse the vocalisation of animals more widely.
"Vocal tract modelling is unfortunately used almost uniquely in human language research but it is an incredibly powerful tool," he said.
Source: http://www.bbc.co.uk/nature/19652679
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