This article is reposted from the old Wordpress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I'll return with fresh material.
It's tempting to think that elephants have their own PR agency. Just last week, their mighty reputation was damaged by the revelation that they are scared away by bees but they have bounced back with a new study that cements their standing among the most intelligent of animals.
Lucy Bates and colleagues from the University of St Andrews have found that African elephants (Loxodonta africana) can tell the difference between different human ethnic groups by smell alone. They also react appropriately to the level of threat they pose.
The Massai, for example, are a group of cattle-herders, whose young men sometimes prove themselves by spearing elephants. Clearly, it would pay to be able to sort out these humans from those who post little threat, like the Kamba.
At the Amboseli National Park in Kenya, Bates found that elephants reacted more fearfully to clothes previously worn by a Massai man than to clean ones or those worn by a Kamba man. She placed the three types of cloth near 18 family groups and watched what happened.
When the first individual caught whiff of a new scent, it raised its head and curled its trunk towards the source of the smell. If they smelled Massai clothes, they moved away particularly fast, travelled about five times further and took more than twice as long to relax. They could clearly tell the difference between the two groups based on smell and reacted more defensively to the dangerous one.
Every single time the elephants smelled Massai on the wind, they moved downwind and didn't stop until they reached tall elephant grass, over 1m in height. They only sought tall grass in about half of the trials with Kamba clothes, and almost none of the trials with clean clothes. To Bates, this was a clear sign of planned action for elephant grass only covers about 7% of Amboseli.
In all cases, the elephants never approached within 10m of the clothes and wouldn't have seen them. They reacted on smell alone. It's possible that the Massai and Kamba exude different pheromones, but their distinctive scents possibly stem from their vastly contrasting cultures.
The Kamba eat meat, vegetables and maize meal. The Massai, on the other hand, subsist mainly on milk and cattle meat and their villages are suffused by the smells of their herds. They also use ochre and sheep fat for decorations. To an elephant's sensitive trunks, the resulting smells must be as different as red and green beacons are to our eyes.
Visual cues worked too - while most African groups wear a wide range of colours, the Massai traditionally wear a striking red. Bates found that when the elephants saw clean, unworn red cloths, they reacted much more aggressively than they did to clean white ones, even though red is a fairly drab colour to elephant eyes.
Bates believes that the smell of Massai triggers a strong fear in the elephants that overrides whatever their eyes tell them. If the elephant sees the distinctive colour of the Massai but doesn't smell them, it's lack of fear allows aggression to come to the forefront.
Seven of the families included individuals that had faced spears over the last 30 years, and two individuals in particular had a history of violence towards Massai cattle. But neither of these factors affected the elephants' reactions. Even groups that were personally inexperienced with Massai spears showed similarly strong reactions to the veterans.
Like the recent bee study, this once again shows that elephants rely heavily on shared knowledge, even between different family groups. Elephants groups have complex social structures and they can recognise individuals in the group by their calls. They appear to recognise the bones of dead elephants and mourn members of their group who pass away.
Many non-human animals including meerkats, vervet monkeys and prairie dogs can classify predators into different groups and react accordingly to the type of threat they pose. But so far, the elephant's ability to split members of a single species into further sub-groups is a unique one.
More on elephants:
Elephants crave companionship in unfamiliar stomping grounds
Reference: Bates, Sayialel, Njiraini, Moss, Poole & Byrne. 2007. Elephants classify human ethnic groups by odor and garment color. 2007. Curr Biol 17, 1-5.