WASHINGTON, Aug. 4 (Xinhua) -- Horses can use their facial expressions, specifically the direction of eyes and ears, to "talk " to other horses, a study said Monday.
Previous work investigating communication of attention in animals has focused on cues that humans use: body orientation, head orientation, and eye gaze, but no one else had gone beyond that, said lead author Jennifer Wathan of the University of Sussex in Britain.
"However, we found that in horses their ear position was also a crucial visual signal that other horses respond to," she said.
"In fact, horses need to see the detailed facial features of both eyes and ears before they use another horse's head direction to guide them."
The new study, published in the U.S. journal Current Biology, challenges theories that animals with eyes to the sides of their heads cannot get information based on the direction of one another 's gaze, she said.
Wathan and the study's senior author Karen McComb took photographs to document cues given by horses when they were paying attention to something.
Then they used those photographs as life-sized models for other horses to look at as they chose between two feeding buckets.
In each case, the horse in the photo was paying attention to one of the buckets and not the other. In some instances, the researchers also manipulated the image to remove information from key facial areas, including the eyes and the ears.
The researchers' observations show that horses rely on the head orientation of their peers to locate food.
However, that ability to read each other's interest level is disrupted when parts of the face -- the eyes and ears -- are covered up with masks.
The ability to correctly judge attention also varied depending on the identity of the horse pictured, suggesting that individual facial features may be important, the researchers reported.
Wathan and McComb planned to continue to explore facial features related to the expression of emotion in their horses, noting that horses' rich social lives and close relationship to humans make them particularly interesting as study subjects.
"Horses display some of the same complex and fluid social organization that we have as humans and that we also see in chimpanzees, elephants, and dolphins," Wathan said.
"The challenges that living in these societies create, such as maintaining valuable social relationships on the basis of unpredictable interactions, are thought to have promoted the evolution of advanced social and communicative skills."