March 21 (UPI) -- Sun bears mimic each other's facial expressions, according to a new study. The subtle form of communication was previously thought to be only practiced by primates.
Sun bears are the world's smallest bear species. They make their home in the forests of Southeast Asia.
Biologists at the University of Portsmouth spent two years observing the behavior and interactions of sun bears in wild-like conditions at a rehabilitation center in Malaysia. Though solitary creatures, sun bears are surprisingly playful.
Their research revealed sun bears, sometimes called honey bears, use facial expressions to communicate, much in the same way humans and apes use facial expressions.
"Mimicking the facial expressions of others in exact ways is one of the pillars of human communication," Portsmouth researcher Marina Davila-Ross said in a news release. "Other primates and dogs are known to mimic each other, but only great apes and humans, and now sun bears, were previously known to show such complexity in their facial mimicry."
Until now, biologists had only observed facial mimicry among humans and gorillas.
Because sun bears aren't closely related to primates, nor do they have a history of domestication, scientists estimate other undiscovered examples of facial mimicry await.
"We are confident that this more advanced form of mimicry is present in various other species," said Davila-Ross. "This, however, needs to be further investigated."
Researchers described their discovery of sun bear facial mimicry in a study published Thursday in the journal Scientific Reports.
Though sun bear interactions are often playful, the mammals spend most of their time alone. Despite their solitary nature, the species evolved the use of facial mimicry.
"This suggests the ability to communicate via complex facial expressions could be a pervasive trait in mammals, allowing them to navigate their societies," Davila-Ross said.
During their two-year study, researchers observed hundreds of instances of play. Interactions were characterized as either gentle or rough play. Bears engaged in gentle play twice as often as rough play, and during gentle play, bears were twice as likely to mimic each other's facial expressions.
"It is widely believed that we only find complex forms of communication in species with complex social systems," said Derry Taylor, a doctoral candidate at Portsmouth. "As sun bears are a largely solitary species, our study of their facial communication questions this belief, because it shows a complex form of facial communication that until now was known only in more social species."
Already elusive, sun bear numbers have declined in recent years as a result of deforestation and poaching pressure. Improved conservation efforts are needed to protect the endangered species.