A new study could take the mystery out of a horse whisperer's job.

The Equine Vocalization Project is compiling a database of horse talk and behavior in an attempt to correlate nuances in their whinnies with differences in their stress levels.

The information could help shed light on the communication styles of other equines, such as donkeys and zebras, and even improve how veterinarians, behaviorists, breeders or other animal handlers relate to horses.

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.