A horse’s neigh may be unique in the animal kingdom. Now scientists know how they do it

NEW YORK– NEW YORK — Horses neigh to find new friends, greet old ones and celebrate happy moments like feeding time.

Exactly how horses produce this distinctive sound – also called neighing – has long eluded scientists.

Neighing is an unusual combination of high and low sounds, like a cross between a grunt and a cry – coming out at the same time.

The serious part wasn’t really a mystery. This comes from air passing over the tissue bands of the voice box which make noise when they vibrate. It’s a technique similar to how humans speak and sing.

But the high-pitched bit is more confusing. With few exceptions, larger animals have larger vocal systems and generally make lower pitched sounds. So how do horses do it?

According to a new study, they hiss.

The researchers slipped a small camera into the horses’ noses to film what was happening inside as they whinnied and made another common horse sound, the softest and most subtle. They also performed detailed scans and blew air through the dead horses’ insulated voice boxes.

The mysterious high-pitched tones of neighing, they discovered, are a kind of whistling sound that begins in the horse’s voice box. The air vibrates the tissues of the voice box while an area just above it contracts, leaving a small opening for the whistle to escape.

This is different from human whistling, which we make with our mouths.

“I never would have guessed there was a wheezing component. It’s really interesting, and I can hear it now,” said Jenifer Nadeau, who studies horses at the University of Connecticut. Nadeau did not participate in the study, published Monday in the journal Current Biology.

Some small rodents like rats and mice whistle this way, but horses are the first known large mammal to have a gift for it. They are also the only animals known to be able to whistle through their voice boxes while they sing.

“Knowing that a ‘neigh’ is not just a ‘neigh,’ but is actually composed of two different fundamental frequencies created by two different mechanisms is exciting,” Alisa Herbst of the Rutgers University Equine Science Center said of the study in an email.

A big lingering question is how horses’ two-tone calls originated. Wild Przewalski’s horses can do something similar, as can elk. But horses farther away, like donkeys and zebras, cannot make high-pitched sounds.

Two-tone neighing could help horses convey multiple messages at the same time. The different neighs may help them express a more complex range of feelings when socializing, said study author Elodie Mandel-Briefer of the University of Copenhagen.

“They can express their emotions in both of these dimensions,” Mandel-Briefer said.

—-

Associated Press video journalist James Brooks contributed to this report.

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.