Horse neighing consists of a unique mix of high and low tones. But how do the large animals produce the high-frequency components of their vocalizations? A study has now solved this mystery: According to this, air flows through the horse’s larynx in two different ways. For the low frequencies, the vocal folds vibrate in a similar way to humans when we talk or sing. The high frequencies, on the other hand, are created by air being forced through the larynx, like whistling. Such a mechanism was previously only known from small animals such as mice. Horses probably use the diverse frequencies to transmit several messages to their peers at the same time.
In general, the following applies in nature: large animals have a deep voice, small animals have a high voice. The reason for this is the physical properties of the vocal folds. Similar to the sides of a guitar, long, thick vocal folds vibrate more slowly, producing lower frequencies; short, thin vocal folds vibrate faster and produce higher frequencies. But some animal species are an exception to this basic principle thanks to special vocal techniques. Despite their size, horses can produce high tones with a frequency in the 1500 hertz range – higher than even an opera soprano could achieve. At the same time, their neighing also contains low frequencies.
Singing and whistling
“In the past, we have found that these two frequencies are important for horses because they convey different messages about the horses’ emotions,” explains Elodie Briefer from the University of Copenhagen. However, it was unclear how the large mammals generate both frequencies, even though the high-pitched sounds should actually not be physiologically possible for them. “To solve this biomechanical puzzle, we had to combine approaches from veterinary medicine and acoustic physics,” says Briefer’s colleague Romain Lefèvre.
Together with her team, Lefèvre and Briefer examined the larynxes of living and deceased horses, evaluated clinical data and carried out acoustic analyzes under various conditions. It turned out that the high and low frequencies of neighing come about through different mechanisms. As with most mammals, the low tones are created by the vibration of the vocal folds, just as with us humans when we talk or sing. The high tones, on the other hand, are more like a whistle – except that the air is not forced through pursed lips, but through a firm gap in the larynx.
Exceptional technology
To prove that tissue vibrations do not play a role in the high frequencies, the researchers alternately blew air and helium through the removed larynxes of deceased horses. Because the speed of sound of helium is higher, the already high-pitched whistling shifted to even higher frequencies – without any changes to the vocal cord vibration. This proves that the high-frequency components of the whinny are caused solely by the turbulence of the air pressed through a narrow gap, without the voice being involved.
Such a sound production technique was previously only known from small animals such as mice and rats. Horses are the first large mammal species in which this whistle was detected. The combination of whistling with lower frequencies based on vocal cord vibrations is also unusual. According to the researchers, this so-called biphonation represents a unique vocal adaptation of horses, which has probably significantly expanded their communicative spectrum. In related species such as donkeys and zebras, however, the high components are missing. “Understanding how and why biphonation evolved is an important step towards elucidating the origins of the amazing vocal diversity of mammals,” says co-author David Reby from the University of Lyon/Saint-Etienne.
Source: Romain Lefèvre (University of Copenhagen) et al., Current Biology, doi: 10.1016/j.cub.2026.01.004