Researchers from Italy and Madagascar studied the singing lemurs, indri, and concluded that these animals possess the ability to tune formants.
It was found that indri open their mouths wider when performing high notes. This causes the resonant frequencies in the animal's tract to shift towards higher values, allowing the formants to match either the fundamental frequency of the sound or its harmonics.
This mechanism is similar to how humans control their voice, as singers regulate their sound by emphasizing specific frequencies through manipulations of the vocal tract.
The results of this study were officially published in the scientific journal PLoS Computational Biology.
