This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: We are often left open-mouthed in awe as an opera singer hits a soaring top note. Now, researchers at the University of Warwick have found that the indri, the world's only known singing lemur, appears to use a strikingly similar vocal technique to hit high notes.
The new study, published in PLOS Computational Biology, provides the first direct evidence that wild indris (Indri indri) coordinate their mouth openings with the frequency of their songs. In short, the higher the pitch of the song, the wider the indris open their mouths to sing it. Found only in the rainforests of Madagascar, indris produce complex, haunting songs that carry across vast distances, strengthening bonds within their social groups and warning neighboring groups to keep their distance.
Human singers are trained to widen their mouths as pitch rises, aligning the resonant frequencies of the vocal tract with the harmonics of the voice and amplifying the sound. This process, known as formant tuning, may serve a similar purpose for the indri. For an animal communicating through thick forest, it could make the difference between a song that carries and one that doesn't.
"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 research team analyzed 83 video recordings of 19 wild indris, combining field audio with markerless motion-tracking technology.
They tracked upper and lower lip positions frame by frame, comparing changes in mouth opening with changes in vocal frequency and finding that indris opened their mouths wider to project higher-pitched vocalizations through the forest. "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 of the 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." Humans and indris last shared a common ancestor approximately 74 million years ago, meaning the similarities in vocal production between the two species are likely the result of convergent evolution, independently arriving at the same solution across deep evolutionary time. Dynamics of jaw kinematics and fundamental frequency suggest vocal tract tuning in the indris, PLOS Computational Biology (2026).
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