When detecting the scent of a Masai, the elephants turned up their trunks to orient themselves to the smell and then stampeded away until they reached cover in the tall grass.

"The degree with which the elephants are able to classify people hasn't been shown before in any animal," said Lucy Bates, a cognitive psychologist at the University of St. Andrews, who worked on the study published in Current Biology.

Working with the Amboseli Elephant Research Project in southern Kenya, the researchers presented the animals with clean clothing and material worn by either a Masai or Kamba tribesman.

They did not stampede when sniffing either clean clothes or those worn by Kamba tribesmen, farmers who pose little threat to the animals, Bates said.

"The reactions between the Masai and the Kamba were so different," Bates said in a telephone interview. "They weren't reacting as if it was the same predator."

To test their reactions further, the researchers presented the elephants with red material, the same colour as the Masai's traditional costume, and plain white clothing.

When the animals spied red, they stamped their feet and shook their heads in an aggressive manner while the colour white failed to spark such aggressive behaviour, Bates said.

"The reaction with the Masai clothes was very intense," Bates said.

The findings could boost conservation efforts in Kenya focused on keeping people and pachyderms apart, Bates said.