A sun bear is seen inside a semi-natural enclosure at a bear rescue center in Tam Dao national park, north of Hanoi, Vietnam, July 22, 2015. (REUTERS/Nguyen Huy Kham)
Sun bears, the smallest of the world's eight bear species, are generally solitary animals, content to spend most of their time alone outside mating season, foraging for fruit, rodents, birds and insects in Southeast Asian tropical forests.
But, scientists said on Thursday, they also possess an unexpected social skill that puts them in elite company alongside humans and some of our close evolutionary cousins: the ability to mimic another bear's facial expressions in a subtle type of communication.
Researchers studied 22 sun bears in spontaneous social play at the Bornean Sun Bear Conservation Centre in Malaysia in outdoor forest enclosures big enough to let the animals decide whether to interact or avoid each other all day.
The bears exactly mimicked facial expressions they saw other bears produce during social play, copying with high precision not only the type of expression but also specific muscular movements such as raising their noses and wrinkling the bridge of their muzzles.
Other than people, facial mimicry has been observed in gorillas, orangutans, two monkey species and domesticated dogs. Until now, only gorillas had been observed showing a degree of precision comparable to the complex facial mimicry of people. But the sun bears proved equally as sophisticated as the gorillas and comparable to people, the study found.
The findings were surprising not only because sun bears are usually solitary but also because they are not closely related to humans.
"It seems that some forms of communication are much more widely shared amongst mammalian species than we previously thought," said Derry Taylor, a comparative psychology PhD student at the University of Portsmouth in England and lead author of the study published in the journal Scientific Reports.
Sun bears, with a black coat and a white or golden patch on the chest, are stocky arboreal omnivores reaching about 4-1/2 feet (1.4 meters) long and 145 pounds (65 kg).
Though they favor solitude in the wild, the bears in the study often engaged in gentle play, with slow grappling actions, and, less often, rough play, with faster actions and behaviors such as hitting and biting. A key difference in the two distinct expressions that the bears mimicked was that one did not display the upper incisor teeth while the other did.
It remains uncertain what messages the bears were conveying to one another, but the mimicry might signal a readiness to transition from gentle to rougher play, Taylor said.