Elephants mourn their dead and engage in long-distance communication using barely audible, low-frequency growls. Now they have been shown to be able to distinguish between different human tribes based on the smell and colour of their clothing.
It is believed to be the first time that any wild animal has been found to have the ability to categorise different sub-groups within the same species depending on the potential threat that they pose.
A study of elephants in the Amboseli National Park in Kenya has found that they react differently to members of the Maasai, cattle-herding pastoralists whose young men sometimes spear elephants to prove their virility, and the Kamba, who are village-dwelling farmers who pose little threat to them.
Scientists from the University of St Andrews and the Amboseli Trust for Elephants in Nairobi conducted field experiments which have shown that the elephants base their distrust of the Maasai on the colour of their traditional clothing - red - and their body scent.
Anecdotal evidence gathered over the past 35 years suggested that the elephants might be able to distinguish between the Maasai and the Kamba, which led the scientists to devise an experiment based on clothing worn for five days by members of each tribe.
"We expected that elephants might be able to distinguish among different human groups according to the level of risk that each presents to them, and we were not disappointed," said Professor Richard Byrne, who led the study published in the journal Current Biology.
"In fact, we think this is the first time that it has been experimentally shown that any animal can categorise a single species of potential predator into subclasses based on such subtle cues," Professor Byrne said.
The scientists subjected elephant herds to different garments - both worn and unworn cloths - and observed the reaction of the animals.
The elephants became significantly more nervous and travelled more quickly away from the Maasai-worn clothing than the clothing of the Kamba. The animals were most relaxed in the presence of unworn cloths.
A typical reaction in the presence of the Maasai clothing was for the elephants to raise their trunks above their heads in the direction of the scent and then move directly downwind of the scent.
They did this even when the clothing was too far away to be seen, so the reaction must have been based on smell alone.
However, when the scientists exposed red and white cloths to the elephants, the animals acted more aggressively to red. This is despite the fact that red is a rather drab colour to an elephant's eye, the scientists said.
Lucy Bates, a member of the research team at St Andrews, said that the elephants appear to be able to assess the level of risk posed by the members of each tribe and adopt the appropriate behaviour based on this assessment. "With any scent present, fear and escape reactions seem to dominate anything else," she said.
Elephants are increasingly becoming a nuisance for farmers in Africa because of the expansion of the human population, and with it agricultural land, so the findings could be useful in terms of helping to avoid future conflicts.
"While elephants can undoubtedly be dangerous when they come into conflict with humans, our data shows that, given the opportunity, they would far rather run away even before they encounter the humans in person," Professor Byrne said.