Elephants may be known for their long memories, but it seems they are incredible listeners, too.
African elephants who hear human voices can tell people of different sexes, ages and even ethnic groups apart, according to a study in the journal Proceedings of the National Academy of Sciences. Such keen ears are necessary when trying to survive in territory marked by human-elephant conflict.
African elephants living in Kenya's Amboseli National Park share land with the Maasai people, who raise and herd cattle.
The two groups sporadically come into conflict over such resources as grazing land and water. Occasionally an elephant will attack cattle or even a human, and Maasai hunters will spear an elephant in response.
But these attacks are random, from an elephant's perspective - so knowing which human is most likely to attack you is a handy skill.
"The elephants can't predict where the people are going to be because they range over these large areas, grazing their cattle," said Graeme Shannon, a behavioural ecologist at Colorado State University who co-led the study. "So they have to respond appropriately."
The researchers took a camouflaged speaker and placed it about 50 metres away from where they expected wandering elephants to end up.
They prerecorded calls from villagers, including Maasai men, women and young boys, saying, "Look, look over there: a group of elephants is coming".
To compare to the Maasai, they also included calls from people known as the Kamba. Since the Kamba are farmers, not cattle herders, they generally come into far less conflict with elephants.
The scientists waited for elephant families to wander within earshot, and videotaped their responses to the recorded voices.
The elephants would react with alarm to the voices of Maasai men - they quickly huddled, protecting the calves, and raised their trunks to sniff for scent.
Recordings from Maasai women or boys didn't earn such a reaction. Nor did the voices of Kamba men.
That's because Maasai men are the most likely to hunt an elephant down, the scientists said.