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Headline: It's the tree tenors! Lemurs use opera singing technique to call across forests
Caption: **VIDEO AVAILABLE: CONTACT INFO@COVERMG.COM TO RECEIVE** BY MARK WORGAN Scientists in Madagascar have discovered some unlikely new opera stars - singing lemurs who use vocal techniques more commonly found at La Scala. Indris, which live only in the rainforests of Madagascar, open their mouths wider as the pitch of their songs rises, according to researchers from the University of Warwick and the University of Turin. The findings provide the first direct evidence that wild indris (Indri indri) coordinate the movement of their mouths with the frequency of their songs. The study, published in PLOS Computational Biology, suggests the animals may use a technique similar to the "formant tuning" employed by trained opera singers. Human vocalists, like sopranos or tenors, are taught to widen their mouths as they sing higher notes, helping to align the resonant frequencies of the vocal tract with the harmonics produced by the voice. For indris, a similar mechanism could help their calls travel through dense rainforest. Indris produce complex songs that can carry over long distances. Their vocalisations are thought to help strengthen social bonds within groups and communicate with neighbouring groups. Researchers analysed 83 video recordings of 19 wild indris, combining audio recordings from the field with markerless motion-tracking technology. They tracked the positions of the animals' upper and lower lips frame by frame and compared changes in mouth opening with changes in vocal frequency. The analysis found that the indris opened their mouths wider when producing higher-pitched vocalisations. "Every time the pitch of an indri's song rose, we could see its mouth opening wider, frame by frame," said Dr Chiara De Gregorio, corresponding author and Honorary Research Fellow at the University of Warwick. "It's the kind of fine-tuned coordination between voice and body that we usually associate with trained human singers, not with a lemur singing from the forest canopy." The researchers say the behaviour could help indris amplify particular frequencies in their calls, potentially making them easier to hear through thick forest. The use of video was central to the study because audio recordings alone cannot show how an animal's vocal movements are produced. “Applying markerless pose estimation to footage recorded in the wild allowed us to look not just at the sounds indris make, but at the physical movements behind them," said first author Dr Filippo Carugati, University of Turin. "It let us study how the face and mouth move while an animal is singing, almost frame by frame, and connect those movements directly to changes in pitch. That's something you simply can't capture by listening to the audio alone." The findings suggest that the relationship between vocal pitch and mouth movement is not simply a feature of human singing. Instead, it may represent an example of convergent evolution, in which unrelated species independently develop similar traits or behaviours because they face comparable challenges. Humans and indris last shared a common ancestor about 74 million years ago. The researchers therefore say the similarities in how the two species produce high-pitched sounds are unlikely to have been inherited from a recent common ancestor. For humans, controlling the shape of the vocal tract is an important part of producing and projecting different sounds. For indris, the ability to modify the shape of the mouth while singing may similarly help them control the acoustic properties of their calls. The researchers say further work will be needed to establish exactly how the mouth movements affect the sound produced by indris and what role the behaviour plays in communication in the wild. The study nevertheless provides a new example of how detailed observations of animal behaviour can reveal similarities between vocal communication in species separated by tens of millions of years.
Keywords: feature,photo,video,lemurs,nature,natural world,opera
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