Researchers have discovered that African elephants can distinguish different people groups and gauge whether or not the humans are dangerous just from hearing them talk.

Working with around 1,500 elephants roaming Kenya's Amboseli National Park, the researchers found that elephants can tell if a human voice is male or female and if it belongs to a child or an adult, USA TODAY reported.

"They're using vocal information from another species--us--and they're using that to discern a threat," said study co-author Graeme Shannon, a behavioral ecologist at Britain's University of Sussex, as quoted by USA TODAY. "That takes really advanced cognitive abilities. ... These are subtle differences these elephants are attending to."

The elephants used in the study live near two groups of people: the Maasi, who used to spear elephants frequently and now attack the animals on occasion, and the Kamba, peaceful farmers who aren't a threat.

To test whether the elephants could tell the different ethnic groups apart, the scientists disguised loudspeakers with palm leaves and put them near a herd. The speakers played a human voice saying, "Look, look over there, a group of elephants is coming," and the elephants reacted in different ways depending on the voice.

The recording of a Masaai man put the elephants on alert; they bunched together and smelled the air, waiting for a possible attack. But they had little reaction to a Kamba man or women and children from either people group, who didn't historically pose a threat.

The scientists then further tested the animals' ability to distinguish voices by toying with the recording of a Masaai man's voice to sound higher and more like a woman's. The elephants still reacted as if the voice hadn't been altered, which implies that "they are picking up gender signals more accurate than those used by humans," USA TODAY reported. 

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