"You would like to find that you get a particular whinny for a particular situation," said physicist David Browning, an adjunct professor at the University of Rhode Island, who along with Peter Scheifele, a research associate at the University of Connecticut, announced their project last week at the Acoustical Society of America in Providence, RI.
Unlike the monotonal vocalizations of cows, goats, and sheep, horses emit a range of sounds from snorts, blows and sighs to whinnies, which also come in the form of nickers and squeals.
Browning's initial acoustical studies have shown that whinnies have the greatest changes in frequency and could contain information about specific situations.
When they are stressed, their vocalizations peak into a high-pitched screams; when they are calm, their whinnies modulate in the middle tones.
But scientists are still not sure if the changes in frequency can be connected to more specific conditions.
Browning and Scheifele have begun compiling a database of horse vocalizations — from their own recordings and from those of other researchers. The vocalizations are analyzed with acoustic software that plots the sound over time.
They categorize the vocalizations by behavior in order to answer some basic questions. For example, horses have a good memory and can recognize friends, both human and horse. Browning would like to know if the whinny they make when they see someone they like is different from one they make upon seeing someone they don't like.
As part of the project, Browning will also be collecting vocalizations of three species of zebra — one that brays like a donkey, one that whinnies like a horse, and one that barks like a dog — to try and get a more complete picture of equine vocalizations.
Sarah Ralston an associate professor at the Equine Science Center at Rutgers University, isn't sure how much the study will contribute to the practicality of handling horses. But she does think that comparing the vocalization of horses and zebras could provide some insight into the social organization of different equines.
"One [zebra] is like a horse with harems and lives in groups, whereas another is more solitary. Differences in vocalizations might reflect differences in the social organization," she said.
