London, September 12 : A new study has suggested that elephants have their own global positioning system (GPS), in the form of powerful rumbles, which are mostly too low in pitch for humans to hear, to keep family members from wandering too far.
According to a report in New Scientist, Katherine Leighty, a behavioural ecologist at Disney's Animal Kingdom in Lake Buena Vista, Florida, led the study.
African elephants form tightly knit families centred around dominant females. Family members spread out while looking for food but always reunite, according to Leighty.
Research on the elephants in the wild has hinted that their low-frequency calls, which can travel more than 2 kilometres, work like GPS, she added.
But, proving that in the wild requires tracking the movements and subsonic calls of multiple elephants - all relative to one another.
For this reason, Leighty and her colleagues studied five captive elephants living in 4-hectare outdoor enclosure within a wildlife sanctuary owned by Walt Disney.
"They're not related by blood, yet some of them seemed to have formed social bonds," she said.
The researchers, including bioacoustic scientist Joseph Soltis, attached microphone collars to each elephant, along with a satellite tag, which allowed the scientists to sync the movements of each animal in response to a rumble.
The team found that after one elephant rumbled, another moved closer to it. If the two elephants were good friends - determined by how often they stuck together - and the second elephant rumbled back, the elephants moved even closer to one another, compared to less convivial pairs.
"Everybody knows that this is how the (rumbles) function, but this really proves it in a really clear way," said Mya Thompson, a behavioural ecologist at Cornell University in Ithaca, New York, who also studies African elephant communication.
But the elephant "GPS" requires each animal to have a unique call.
"We haven't really nailed down precisely what structures in the calls allow animals to distinguish familiar callers from unfamiliar callers," said Thompson. "We know they can do it, but we're not presently sure how," she added.
According to Soltis, the rumbles almost certainly convey information besides "here I am" or "come hither". When less chummy elephants got too close, rumbles seemed to push them apart.
The researchers have also found that subordinate elephants raise the pitch of their rumbles in response to the calls of dominant animals.