New research has discovered that horses’ famous neighing is made by combining two sound frequencies at the same time.
Horses produce your characteristic neigh using a surprisingly sophisticated vocal trick: they “sing” and “whistle” at the same time.
A new published in the journal Current Biology reveals that horses generate two independent sound frequencies in a single sound emitted — a rare phenomenon known as biphonation — allowing them to convey multiple messages in a single vocal signal.
The research team found that the low-frequency component of neighing is produced by vocal fold vibrations in the larynxin a similar way to human singing. At the same time, horses generate a high-pitched sound through a type of internal whistle in the larynx. This dual mechanism creates the neigh’s peculiar two-layer structure, which scientists believe evolved to transmit different types of information simultaneously, such as emotional state and individual identity.
“Until now, we didn’t know how horses physically produced these two frequencies at the same time,” he said. Elodie Brieferfrom the University of Copenhagen. Previous studies had already demonstrated that the two frequency layers in a neigh carry different emotional nuancesbut the biomechanical basis behind these sounds remained a mystery. The findings provide direct evidence that the two components are created by distinct anatomical mechanisms.
Although large mammals generally produce lower-pitched sounds due to their larger vocal tracts, horses are an exception. Your neighs contain unexpectedly high frequencieswhich has intrigued researchers for years.
Combining veterinary anatomy, acoustic analysis and clinical data, the team identified the source of the high-pitched sound as a “laryngeal whistle“, which consists of a turbulence of airflow within the larynx itself. Although small rodents are known to whistle in this way, horses are the first large mammals to demonstrate the use of the same mechanism and the only animals known to combine whistling with vocal fold vibration simultaneously, says the .
To confirm the discovery, researchers performed controlled airflow experiments on excised horse larynxes. When helium replaced normal air, the high-frequency hiss moved to higher frequencieswhile the sound of the low-frequency vocal folds remained unchanged. The clear split in behavior confirmed that two independent sound sources were at work.
The findings may help explain why horses have such a rich vocal repertoire compared to their close relatives. Przewalski’s horses, wild relatives of domestic horses, also produce biphonal neighs, while donkeys and zebras appear to lack the high-frequency component.
