How horses whine has long been a mystery. Now scientists think they know the answer

Horses neigh by making sounds in a unique way not seen in other animals

By Jackie Flynn Mogensen edited by Claire Cameron

How horses whine has long been a mystery. The sound is quite different from any other in the animal kingdom. And now scientists think they’ve discovered why: horses whine by producing sounds at two frequencies at the same time – much like singing and whistling at the same time.

The findings, which were published on Monday i Current Biology, suggests that horses produce sounds at two frequencies in two different ways in the larynx, or voice box. A low-frequency sound of around 200 hertz is produced by vibrating the vocal cords, just as we do when we sing. And a high-frequency sound of more than 1000 hertz is produced by whistling in the larynx.

“We now finally know how the two fundamental frequencies that make up a whinny are produced by horses,” Élodie Briefer, an associate professor in the Department of Ecology and Evolution at the University of Copenhagen and a co-author of the paper, said in a statement.

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In general, the larger an animal – and the larynx – is, the lower the sound frequency it produces. Meanwhile, smaller creatures, such as mice, produce high-frequency whistles. But this study suggests that horses are unique in their ability to whistle and vibrate their vocal cords at the same time, the authors write.

“This is going to be a landmark in stimulating research into equine vocalizations,” Sue McDonnell, an assistant professor of reproduction and behavior at the University of Pennsylvania, who was not involved in the research, told New York Times.

The results support a theory that horses may have evolved to communicate multiple messages in a single vocalization, write the study authors.

“Previously, we found that these two frequencies are important to horses, as they convey different messages about the horses’ own emotions,” Briefer said in the same statement. “We now have compelling evidence that they are also produced through different mechanisms.”

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