Ai, a 27-year-old chimpanzee in western Japan, watches another chimp yawn, quickly rolls back her head and soon is showing the pink inside of her mouth in a gaping yawn of her own.
"It's another good example of how chimpanzees are so like us," said Tetsuro Matsuzawa, professor at the Primate Research Institute at Kyoto University who took part in the Japan-based study.
The study, published this month in the British online journal The Royal Society Biology Letters, says that out of six chimpanzees under observation, two clearly yawned repeatedly in response to videos of other chimps yawning.
Three infant chimps accompanying their mothers did not respond at all, it said.
Meanwhile, none yawned in response to images of other chimps just opening their mouths.
The pattern fits that of humans, Matsuzawa said.
When people watch yawning videos, roughly half yawn in response, while children under five do not appear to find yawning contagious, he said.
Contagious yawning is thought to be a result of empathy and self-awareness, both of which require a sophisticated intellect, the study concluded.
Previously, it was believed that only older humans yawned contagiously because young children and animals did not have the intellectual development necessary.
But the study said its findings provide further evidence that apes may possess an advanced level of self-awareness and empathy like mature humans.
Matsuzawa said the next step was to see whether chimpanzees found human yawns contagious, predicting that they would.
"Humans have a strong belief in our differences," Matsuzawa said. "Objectively, we should be one member of the apes."