The scientists also deduced that elephants might employ their keen sense of smell to distinguish Maasai from Kamba.

Their body odors likely differ because Maasai eat substantial amounts of milk and occasionally cattle blood and beef while the Kamba diet consists of vegetables and maize, along with some meat.

Also, unlike the Kamba, the Maasai use ochre and sheep fat in body decorations.

The researchers had heard of several instances of elephants reacting "to even faint signals of Maasai, with elephants running away from Maasai men that were several kilometers away," said cognitive psychologist Lucy Bates at the University of St. Andrews in Scotland.

The pachyderms even stayed away from a vehicle "for several days after Maasai men had been carried in it."

Cognitive psychologist Richard Byrne at the University of St. Andrews, along with Bates and colleagues, tried displaying clean, unworn red and white cloths on bushes in Amboseli. They found elephants behaved significantly more aggressively toward the red cloths.

"We think that this is the first time that it has been experimentally shown that any animal can categorize a single species of potential predator into subclasses based on such subtle cues," Bates said.

The researchers also presented elephants with red clothing that had been worn for five days by either a Maasai or a Kamba man.

The pachyderms reacted with greater fear toward the Maasai-scented clothing — they moved faster away and farther away, fleeing toward tall grass for cover, and took significantly longer to relax after they stopped running.

The differences the researchers saw between elephant responses to sights and smells might relate to the amount of risk the pachyderms sense.

Future research can focus on "what cues in the garments the elephants are attending to — what specific smells signal Maasai and Kamba? What aspect of the red cloths do the elephants respond to — the brightness, the hue?" Bates said.

Moreover, "we don't know how many ethnic groups the elephants can discriminate, or how elephants respond to females of these groups — both of which would be interesting questions to answer," she added.

The scientists, collaborating with the Amboseli Elephant Research Project, detailed their findings online Oct. 18 in the journal Current Biology.