Sun Bears Copy Each Other's Facial Expressions—A Behavior Only Previously Seen in Humans and Gorillas

bear pic
A mature female sun bear in Malaysia which researchers studied. Daniela Hartmann

Scientists have found sun bears can precisely mimic each other's facial expressions, in the first display of such behavior to be spotted in animals other than humans and gorillas.

The study published in the journal Scientific Reports questions the idea that only species with complex social systems —like humans—can exhibit this behavior.

Also known as honey bears, the elusive and therefore little-understood species live in the tropical forests of Southeast Asia and rarely socialize outside of mating.

Researchers studied 22 sun bears aged between 2 to 12 at the Borean Sun Bear Conservation Centre in Malaysia. The team filmed the animals as part of their investigation, which took place in enclosures large enough to allow the bears to isolate themselves or be as social as they pleased.

The team wanted to understand how the animals used facial mimicry: where an animal nearly or exactly copies the expressions of a counterpart.

They found sun bears do in fact use their faces to communicate. During play, the animals showed two expressions: baring or concealing their incisor teeth, respectively. The bears copied one another's expressions most when they were playing gently, the scientists found.

While primates and animals like dogs imitate one another, researchers believe sun bears are the first discovered to so such levels of precision outside of humans and gorillas.

Derry Taylor, study co-author and a Ph.D. candidate at the University of Portsmouth in England, told Newsweek: "Humans show complex patterns of facial mimicry—routinely mimicking not only the facial expressions of others, but precisely mimicking subtle muscular movements also. It is widely believed that we only find complex communication in species with complex social systems.

"Our recent finding of complex facial mimicry in sun bears tells us that there is a little more to this story. Sun bear facial mimicry outstrips facial mimicry shown by more social species with regard to precision, yet sun bears live largely solitary lives in the wild. This raises the possibility that sophisticated facial communication might be a trait widely shared among mammals."

However, Terry told Newsweek the study was limited as it was not clear what the function of these expressions was. He suggested sun bears might copy expressions to signal they are ready to transition into rougher play, but said the data does not currently answer this question.

"We found that exact facial mimicry was much more common in gentle play compared to rough play, and we know that gentle play often builds up into rough play. In other species, when play behavior is not accompanied by play signaling, play often escalates into aggression," he said.

Commenting on how the research contributes to our wider understanding of animal communication, Taylor said the study brings two ideas to the fore.

"One possibility raised by the study is that sophisticated forms of communication might be more widely shared among mammalian species than previously thought, which indicates the widely held belief that complex communication is only present in species with complex social systems is not quite the whole story.

"Alternatively, it could be that there are deeper complexities in the communication systems of more social species that are yet to be discovered."

Sun bears are classed as a vulnerable species as numbers in the wild, and are dropping due to factors including deforestation, poaching, and pest control by farmers, according to National Geographic. The team hopes the research will help with conservation efforts for the creature.

The research is the latest to investigate how animals use their faces to communicate. A 2017 study published in the journal Scientific Reports, also by researchers at the University of Portsmouth, indicated dogs move their faces more when they are being watched by humans.

The authors concluded the facial movements of dogs might not be involuntary "but rather potentially active attempts to communicate with others."