Stomping elephants 'communicate seismically'
By Andrew Quinn
San Francisco - When an elephant puts its foot down, people listen. And so, apparently, do other elephants - using their toenails to sense messages sent from as far as 32km away.
A new study by Stanford University researchers indicates that elephants use foot-stomping and vocal rumblings as part of an elaborate system of seismic communication, sending vibrations through the ground to other elephants far beyond the reach of audible sound.
"If they are sensing these messages in the ground, it radically changes our perspective how far they can communicate," Caitlin O'Connell-Rodwell, a visiting scholar at the Stanford Center for Conservation Biology said in an interview on Monday. "They may be communicating at far greater distances than we thought."
O'Connell-Rodwell's study, published in the December issue of the Journal of the Acoustical Society of America, sheds new light on how elephant herds transmit messages - sensing greetings or warnings of danger through their feet.
By studying separate groups of elephants in Africa, India, and in captivity in Texas, the Stanford researcher found indications that elephants have a highly developed set of seismic signals, creating ground vibrations both through their vocal calls, which create a low level rumbling, and by stomping their feet in mock charges.
Other animals, ranging from certain types of moles and seals to insects, fish, and reptiles, are known to use seismic signals to find mates, locate prey or establish territories.
But the elephants' methods of seismic communication appear to be more complex, and travel far greater distances.
O'Connell-Rodwell said that the seismic waves created by various elephant actions - ranging from foot-stomping warnings to vocal calls of greeting - were recreated and transmitted through the ground to see if elephants would display the same reaction if no audible sound were present.
The results showed that the elephants, particularly female ones, picked up the signals and reacted.
"We think they're sensing these underground vibrations through heir feet," O'Connell-Rodwell said. "Seismic waves could travel through their toenails to the ear via bone conduction, or they may be using seismic sensitivity in their trunk. It may be a combination of both."
Earlier elephant studies have shown that they can produce low-level 20 hertz vocal rumblings that can travel up to 10km through the air under ideal conditions.
Subsequent studies showed that these rumblings themselves create a seismic "echo" in the earth, where the vibrations travel even greater distances. These vibrations are also created by the foot-stomping and ear flapping of mock elephant charges, which the animals use as a defence mechanism when danger is perceived.
"Based on our mathematical models, we estimate that seismic signals produced by elephants can travel between 16 - 32km in the ground," O'Connell-Rodwell said.
She added that current evidence indicated that seismic signals conveyed basic information about where elephants are and what their mood is - enabling elephants at some distance to sense fear or anger.
"Whether or not they can discriminate individuals in the ground is something that we are trying to do in the future with more studies," O'Connell-Rodwell said.
Already, observation of elephant behavior in Angola hinted that seismic signals may travel even farther, with thirsty elephant herds there detecting and moving toward thunderstorms as far as 160km away.
O'Connell-Rodwell said evidence of seismic communication was found in both Asian and African elephants, and could lead to a far broader understanding of how all sorts of animals communicate in the wild.
"It really opens the door to (seismic communication among) other mammals," O'Connell-Rodwell said. "We picked the one animal that was the most obvious - because elephants are so large, and so heavy. But we are also looking for this possibility in rhinos, possibly in bison, and possibly in lions," she said. - Reuters