How do horses whinny?

A horse’s whinny is a distinctive and instantly recognizable sound, which the animals use to communicate with each other and express emotions. As Smithsonian magazine recently reported, this unique vocalization has long puzzled scientists, since it includes both high- and low-pitched components.

Now researchers say a horse makes the low-pitched part of its whinny by vibrating its vocal cords — similar to how humans speak and sing — and the high-pitched part by whistling with its voice box, according to a new paper published in the journal Current Biology. This marks the first known example of a creature that can make these noises simultaneously.

In 2015, scientists reported that a horse’s whinny contains two distinct sounds — one high-pitched, one low-pitched — that the animal produces simultaneously. The realization that horses can make high-frequency sounds was perplexing, because vocal pitch tends to be related to body size in a specific way: Large animals generally make lower-pitched sounds, whereas small animals make higher-pitched ones.

“The rule of thumb is that the lower the frequency the animal can produce, the more the animal sounds like, 'I’m fit, I’m big, I’m bad, you don’t want to mess with me,’” Peter Scheifele, a neuroaudiologist at the University of Cincinnati College of Allied Health Sciences, told the Australian Broadcasting Corporation. Scheifele was not involved in the new research.

For the new study, scientists slid an endoscopic camera through live horses’ noses to get an up-close look at their larynxes as they made sounds. The animals’ vocal cords vibrated whenever they made lower-pitched sounds but didn’t move when they produced higher-pitched ones, reported The New York Times. But during high-pitched vocalizations, the muscles above the vocal cords strongly contracted, per ABC.

Based on these results, the researchers suspected the high-pitched part of the whinny was an aerodynamic laryngeal whistle. To confirm that hunch, they blew compressed air and helium through larynxes removed from deceased horses, then compared the frequencies of the sounds produced by the two gases.

The high-frequency component got much higher when they used helium, confirming the sound was indeed a whistle.

The findings open the door for a wide variety of future research projects. 

Read the full Smithsonian magazine article. 

Featured image at top: The Black Hills Wild Horse Sanctury in South Dakota is home to more than 700 wild horses. Photo/Black Hills Wild Horse Sanctuary.