Horses use a silent form of communication that involves moving, and paying attention to, eyes and ears, a new study has found.
The research, published in the journal Current Biology, shows how animal ears don't just move to better hear sounds. The movements have meaning to other horses.
"Most significantly, our results demonstrate that animals with large, mobile ears can use these as a visual cue to attention," co-authors Jennifer Wathan and Karen McComb wrote.
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Human ears aren't mobile, so scientists in the past hadn't paid much attention to ears as a means of communication in other animals.
As Wathan, a researcher at the University of Sussex, explained in a press release, "Previous work investigating communication of attention in animals has focused on cues that humans use: body orientation, head orientation, and eye gaze; no one else had gone beyond that."
"However, we 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."
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She and McComb found this out after taking life-size photographs of horses while the horses were paying attention to something. The researchers then used the photos as models for other horses to look at as they chose between two feeding buckets. In each case, the horse photo was positioned to look at one of the two buckets.
In some instances, the researchers also manipulated the giant horse photos so that some features, such as the eyes and ears, were missing.
The study determined that horses rely on the head orientation of their peers to locate food, but that this ability is disrupted when eyes, ears, or both are covered up. The positioning of the ears, as well as the direction of the horse's gaze, therefore also communicates important information.
Horses must also use such information to identify threats, to determine where a herd might move next, to monitor foals and for other purposes.
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"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.
She added, "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."
Photo: Closeup of a horse. Credit: Wikimedia Commons