Animals use their mobile ears to detect sounds, and determine the direction of predators. But a new study shows that horses may use their ears to convey visual clues, not just to listen for predators and other dangers. Researchers at the University of Sussex found that when horses had free use of their eyes and ears, they would choose a feed bucket which another horse was pointing to; if either their eyes or ears were covered, they would choose a bucket at random.

Horses have ears which can turn almost 180 degrees, like many prey animals. They most likely developed those ears to avoid predators. However, we may have overlooked the importance of those ears in communication, according to a new research study.

The researchers found that horses looked to the direction that the ears of other horses were pointed in for visual cues to convey information. Horses have swiveling ears that can turn from left to right, and these serve not just as a defense mechanism against danger but also as a rich tool for communication.

This study was published in the most recent issue of Current Biology. The team wanted to find out more about the unique ways that horses use their anatomy to talk to each other. "We're interested in how [they] communicate," said lead researcher Jennifer Wathan. "And being sensitive to what another individual is thinking is a fundamental skill from which other [more complex] skills develop."

Wathan did a study of 72 horses with fellow researcher Professor Karen McComb. In order to find out more about how horses communicated, they set up an experiment in which the horse could choose to feed from one of two buckets. Behind the buckets, they put an actual-size photograph of another horse's head which the head facing either left or right. They did three groups of photographs: one where the horse's ears were covered, one where the eyes were covered, and one where the horse's eyes and ears were left uncovered.

The study found that the horse looked at a photo in which the eyes and ears of the other horse were left uncovered, the horse would choose the feed bucket towards which the photograph of the horse was pointing. If either eyes or ears in the photograph were covered the horse would choose a direction at random.

"It seems there's something in the visual cues - from both the eyes and the ears - that are really important," Wathan told BBC News. "Horses have quite rich social lives and relationships with other horses, so they're a good species to look at this in."