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Wild indris tend to open their mouths wider as the frequency of their songs rises, according to a 2026 study. The pattern is consistent with vocal-tract tuning—the way an animal’s mouth and throat shape sound resonances—but the researchers did not directly test whether wider openings make calls louder or carry farther.
What the study found
Indris (Indri indri) are lemurs native to Madagascar, and the 2026 paper describes them as the only known singing lemurs. Their songs are long-distance vocal displays. A University of Warwick summary says the calls help strengthen group bonds and warn neighboring groups; that ecological context comes from the university’s account, not a direct measurement of the mouth-opening study.
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Researchers analyzed 83 video recordings of 19 wild indris—11 females and eight males—from 11 groups at Maromizaha forest and Mitsinjo reserve in eastern Madagascar. The recordings were gathered on expeditions between 2008 and 2024. Using markerless pose estimation based on DeepLabCut, they tracked the upper and lower lips, measured the vertical gap between them frame by frame, and paired those measurements with fundamental-frequency estimates from the matching audio. A statistical model found a significant positive association: greater mouth opening tended to accompany higher fundamental frequency. Carugati et al., PLOS Computational Biology (2026).
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Why opening the mouth may affect a call
The vocal tract—the passage shaped by the throat, mouth, and lips—resonates as sound passes through it. Animals can change its shape, shifting resonant frequencies. This is called vocal-tract tuning. The authors suggest that opening the mouth wider as a song’s frequency rises could help tune those resonances and affect how the sound projects.
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The comparison with opera singers is an analogy about coordinating mouth shape with vocal output. It does not mean indris sing music in the human sense. The study examined the relationship between jaw movement and acoustic frequency, not musicality as people experience it. The University of Warwick describes the finding as an opera singer’s trick; the underlying paper frames it as possible vocal-tract tuning. University of Warwick’s 2026 summary.
What the evidence does—and does not—show
The study measured naturally occurring movements and sounds; it did not experimentally manipulate an indri’s mouth or jaw. Its results support coordination between mouth opening and fundamental frequency, but do not establish that opening the mouth causes a higher pitch. Nor did the researchers directly measure loudness or how far a call travels. Greater sound projection is a proposed possible benefit, not a demonstrated outcome.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How this study builds on earlier work
Earlier research reported correlations between mouth opening, average fundamental frequency, and first formants—resonant frequencies of the vocal tract. It examined 70 songs from 35 indris recorded between 2004 and 2006, with additional video used to describe movements during vocal production. The 2026 study’s distinct contribution is a frame-by-frame quantitative pairing of mouth-opening estimates with frequency extracted from corresponding audio across a newer video sample.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minute| Study | Material | Approach and finding |
|---|---|---|
| Gamba et al. (study record, 2008) | 70 songs from 35 indris, recorded in 2004–2006 | Audio analysis and descriptive video; reported correlations involving mouth opening, average fundamental frequency, and first formants. Università degli Studi di Torino IRIS record. |
| Carugati et al. (2026) | 83 video recordings of 19 indris from 11 groups; expeditions in 2008–2024 | Frame-level lip tracking paired with matching audio; found a positive association between mouth opening and fundamental frequency. PLOS Computational Biology. |
The sample counts describe different units—songs in the earlier work and video recordings in the newer study—so they are not directly comparable as measures of study size. The newer analysis strengthens the quantitative evidence for coordination, while leaving the proposed effect on loudness and transmission distance unresolved.
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