Via their whinnies, horses convey specific info about their identities, including sex, height and weight, say French researchers. Acoustic analyses of whinnies and horses’ reactions to various recorded whinnies also suggest the vocal calls play an important social role and are 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.

Martine Hausberger, director of the Laboratory of Animal and Human Ethology, says her lab focuses on the link between social bonds and auditory communication in various species, including birds, dolphins, and monkeys.

“We realized there were practically no scientific publications on vocal communication among horses, despite the interesting social structure of these animals. 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," she says.

Characterized as a three-part call, with an introduction, climax, and end, the whinny varies in frequency according to sex, the study of 30 adult domestic horses (10 stallions, 10 geldings, 10 mares) reports. 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 reports.

Whinny recordings of some 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 say. The physical reactions of the horses were very sound-specific, varying significantly in terms of attention and attraction.

"Our results show horses recognize the voices of their social partners even when they can’t see them, which explains their reactions when separated," Hausberger says. "If they’re still within hearing range (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 Animal Cognition. See the abstract at www.ncbi.nlm.nih.gov/pubmed/19449192.
-- www.thehorse.com