The secret of the whinny

Ever wondered why your pony’s whinny sounds so special? Scientists have discovered it’s not just one sound – and the way ponies produce it is seriously clever.

If you’ve ever stood in the field listening to a whinny, you might have noticed it’s more than just a squeal or a neigh. It has both a high, almost whistly sound, and a deeper, lower tone. Researchers reporting in Current Biology have discovered that ponies actually create these two sounds in separate ways – at the same time!

The lower sound comes from the vocal folds, the same way humans sing or cats meow. But the higher sound? That’s produced by a whistle inside the pony’s larynx (voice box) – something previously thought to happen only in small animals like mice or rats. Horses and ponies are the first large mammals discovered to do this, and they can combine the whistle and vocal fold vibration simultaneously.

“We now finally know how the two fundamental frequencies that make up a whinny are produced by horses,” says author Elodie Briefer of the University of Copenhagen. “In the past, we found that these two frequencies are important for horses, as they convey different messages about the horses’ own emotions. We now have compelling evidence that they are also produced through distinct mechanisms.”

To confirm this, researchers carried out clever experiments using excised horse larynges. By blowing air – and even helium – through them, they were able to show that the high-frequency whistle and the lower vocal sound are created independently. As expected, the whistle pitch changed with helium, but the lower tone stayed the same.

“When we blew helium through the larynges for the first time, the frequency shift was immediately obvious, and we knew we’d solved the mystery,” says author William Tecumseh Fitch of the University of Vienna. “We were thrilled!”

This unusual double sound, known as biphonation, probably evolved so ponies can send more than one message at the same time – maybe about their mood, location, or intentions. Even wild Przewalski’s horses can do it, while donkeys and zebras generally cannot.

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