Horses use both eyes and ears as tools for communication, a new study reveals.
Communication between horses has focused on sounds, as well as body and eye direction - the same tools humans employ to convey information. This new investigation shows the importance of ear movements in communication by horses.
"Previous work has focused on head and eye direction, overlooking the fact that many mammals have obvious and mobile ears that could act as a visual cue to attention," researchers wrote in an article announcing their study.
Biologists previously believed that horses and other animals with eyes on the sides of their heads could not detect the direction another member of their species was gazing. This new study upends that idea, showing the animals are capable of making that distinction.
"[W]e found that in horses their ear position was also a crucial visual signal that other horses respond to. 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," Jennifer Wathan from the University of Sussex said.
Researchers took photographs of horses as they paid attention to an object. These images were then used as realistically-sized models. These were placed in front of horses as they were selecting from a pair of feed buckets. In each trial, the model was arranged so it looked like it was paying attention to one of the two buckets. In some of these models, the eyes or ears of the horse were blocked from view, to test the contributions to communications through these body parts. The ability to determine the location of food was also diminished or enhanced, depending on the identity of the horse used as the model. This suggests that individual facial features could also play an important role in conveying information between equines.
Horses do pay attention to the direction another horse's head is pointed to garner information about a potential food source, the study found. However, that communication was severely hindered when eyes or ears were blocked from view.
A followup study will examine how the emotional state of the highly-social animals is conveyed in their facial expressions. Horses have a complex social life, and bonding relationships with humans and other members of their species.
"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. There is a general interest in studying species with this social structure," Wathan said.
Study of horse communication systems using ears and eyes was published in the journal Current Biology.
