Overview
- In research published February 23 in Current Biology, scientists show horses produce two independent frequencies at once, with a low tone from vibrating vocal folds and a high tone from a laryngeal whistle.
- Endoscopic observations in live horses found vocal folds active during low notes but stationary during high notes as muscles above the folds tightened.
- Excised-larynx experiments alternating air and helium shifted only the high-frequency component upward, isolating an aerodynamic whistle as its source.
- Horses emerge as the first large mammals known to produce a laryngeal whistle while simultaneously vibrating their vocal folds, a rare case of biphonation.
- Comparative data indicate Przewalski's horses share this dual mechanism, whereas donkeys and zebras appear to lack the high-frequency element, and researchers suggest the two tones may convey separate signals.