Indri lemurs, native to Madagascar and known for their haunting forest songs, appear to sing using a technique similar to that used by trained opera singers, according to new research. Scientists analyzing dozens of video recordings with motion-tracking technology found that the lemurs widen their mouths as the pitch of their songs rises, helping them manipulate resonance and project sound through dense forest environments. The phenomenon, known as formant tuning, is a technique that human singers use to project sound more powerfully. Researchers say this marks the first direct evidence of such vocal-tract coordination in a non-human primate, suggesting the lemurs may have evolved the technique independently to help their calls travel through dense forest canopy. The findings build on earlier work showing young indris learn to sing much like human children do. Although humans and indris share a common ancestor tens of millions of years ago, scientists believe this singing strategy developed independently in each species.