Sun bears are the smallest of all bear species, growing about 5 feet (1.5 meters) long and weighing up to 150 pounds (68 kilograms). They are usually solitary creatures, feeding on a variety of insects, honey and fruits in their native Southeast Asian rainforests.
Yet these small, mostly solitary bears have revealed some big insights about communication and social sensitivity in mammals, according to a new study published in the journal Scientific Reports. Sun bears can exactly mimic each others' facial expressions, the study's authors report, the first time such precise facial mimicry has been seen beyond humans and gorillas.
"Mimicking the facial expressions of others in exact ways is one of the pillars of human communication," says co-author Marina Davila-Ross, a researcher of comparative psychology at the University of Portsmouth in the U.K., in a statement about the findings. "Other primates and dogs are known to mimic each other, but only great apes and humans were previously known to show such complexity in their facial mimicry."
The study is based on the coded facial expressions of 22 sun bears, ranging in age from 2 to 12 years old. They were recorded during spontaneous social play sessions at Bornean Sun Bear Conservation Centre in Malaysia, where enclosures are large enough that the bears can decide for themselves whether to interact with one another.
Although sun bears are typically solitary, they do have a social side. The bears in this study joined in hundreds of play sessions, with more than twice as many involving gentle play compared with rough play. They were more likely to use precise facial mimicry during gentle play, which the researchers say might help two bears fortify their social bonds, or agree to play more roughly.
But since this kind of social interaction is relatively uncommon for sun bears, especially in the wild, it raises questions about what other subtle communication skills we might be overlooking in other mostly solitary animals. "What's most surprising is the sun bear is not a social animal," Davila-Ross says. "In the wild, it's a relatively solitary animal, so this suggests the ability to communicate via complex facial expressions could be a pervasive trait in mammals, allowing them to navigate their societies."
Also known as honey bears, due to their penchant for raiding beehives, sun bears are listed as Vulnerable by the International Union for Conservation of Nature. Their numbers are declining for several reasons, including poaching, habitat loss due to deforestation, and retaliation from farmers for eating their crops. Sun bear mothers are also increasingly killed so their cubs can be taken into captivity, either as pets or for the widely condemned practice of "bile farming." By raising their public profile and revealing a relatable degree of social sophistication, research like this could be a useful tool in protecting the species.
And, as co-author and University of Portsmouth Ph.D. candidate Derry Taylor explains, there are also broader implications. Many of the social skills and subtleties that seem unique to humans and our close relatives may be more common than we thought.
"Sun bears are an elusive species in the wild and so very little is known about them. We know they live in tropical rainforests, eat almost everything, and that outside of the mating season adults have little to do with one another," Taylor says. "That's what makes these results so fascinating — they are a non-social species who, when face to face, can communicate subtly and precisely."