The sun bears were making faces at each other. And that was a bit of a surprise.

Comparative psychologists have been studying the facial expressions of primates like orangutans and gorillas for years. They have evolved in complex societies and thus need to be able to convey their joy, anger, and other emotions to their companions. But nobody had thought to look at creatures like sun bears, who live mostly solitary lives.

Marina Davila-Ross, a primatologist at the University of Portsmouth in England, and her colleagues learned that a handful of the Southeast Asian bears, which primarily live alone in the wild, were in a rehabilitation center near the orangutan center in Malaysia where Dr. Davila-Ross was doing research.

Curious about whether facial communication was more common in the animal kingdom that people thought, they deployed cameras to capture hours of footage of the bears interacting with each other. In a study published Thursday in Scientific Reports, they say that sun bears do use facial expressions to communicate, suggesting that the capacity to do so may be widespread, and that social creatures do not have a monopoly on expressing themselves this way.