Study: Horse Whinnies Packed with Information

Through their whinnies, horses convey specific information about their identities, including sex, height, and weight, according to French researchers. Acoustic analyses of whinnies and the reactions of horses to various recorded whinnies also suggest that the vocal calls play an important social role and appear to be unique to each horse.

This is the first study of its kind in horses, which are historically considered to be dependent on sight as opposed to hearing for their social communication, the researchers reported.

"Our laboratory focuses on the link between social bonds and auditory communication in various species, including birds, dolphins, and monkeys," said Martine Hausberger, PhD, director of the Laboratory of Animal and Human Ethology, a branch of the French national research center (CNRS) and of the University of Rennes 1. "We realized there were practically no scientific publications on vocal communication among horses, despite the interesting social structure of these animals. We felt compelled to look into this, and what we found was that the whinny is a complex call full of relevant social information. It might even be a signature call for each individual."

Characterized as a three-part call, with an introduction, climax, and end, the whinny varies in frequency according to sex, the study reported. Stallions have low-pitched frequencies whereas mare and gelding calls are higher. Interestingly, the two intact stallions of their study, which were subordinate to other stallions in their social group, also had high-frequency calls similar to that of mares, Hausberger’s team reported. All 30 horses in the study were either privately owned or belonged to a riding club.

Whinny recordings of some of the study horses were played back on an iPod to isolated study horses to observe their reactions. The listeners were clearly able to recognize the social category of the caller, whether it was a horse they knew well, knew from a distance, or didn’t know at all, the researchers said. The physical reactions of the horses were very sound-specific, varying significantly in terms of attention and attraction.

"Our results show that horses recognize the voices of their social partners even when they can’t see them, which explains their reactions when they are separated," Hausberger said. "If they’re still within hearing range (1 km / 0.6 mile) of each other, their reactions are going to be strong."

The study, "Horse (Equus caballus) whinnies: a source of social information," was published in the September edition of Animal Cognition. The abstract is available online.  

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