for National Geographic News
A researcher from California went to Namibia, Africa, last month to check on the vibes elephants put out and pick up. She theorizes that by making the ground rumble, the 6-ton (5,400-kilogram) animals are able to communicate over distances upwards of 20 miles (32 kilometers).
Such signals could warn other elephants of predators, help a lonely elephant find a mate, or direct them towards food and water.
Caitlin O'Connell-Rodwell, a biologist at Stanford University in Palo Alto, California, developed her theory in 1992 based on behavioral observations made while studying elephants in Namibia's Etosha National Park.
"I noted that elephants appeared to pay a lot of attention to the ground with their feet, shifting their weight and leaning forward, sometimes lifting a foot off the ground. This behavior corresponded to a period prior to the arrival of another herd," she said.
Over the last ten years, O'Connell-Rodwell has collected a host of scientific evidence to support her hypothesis. She returned to the arid grasslands of Namibia in June to refine her theory by conducting detailed experiments on how the seismic signals travel and how the elephants react to them.
Drumming, Stomping, and Communicating
Returning from Africa in 1992, O'Connell-Rodwell shared her theory with her Ph.D. advisor, Lynette Hart, a biologist at the University of California at Davis, and Byron Arnason, a geophysicist in Austin, Texas.
"From Byron Arnason's work, I was familiar with seismic exploration and the elastic responsiveness of the earth," Hart said. "For me the excitement was in combining the perspectives, acquiring some geophones from his garage, and exploring a new array of questions."
The team set out to determine whether elephant vocalizations and mock chargesdisplays of ground stomping, ear flapping, and screaming designed to frighten off predators such as lions and hyenaswere transmitted through the ground.
"It turns out that elephant vocalizations and mock charges do indeed travel in the ground," O'Connell-Rodwell said. The sounds and charges transmit in the low frequency range of 20 hertz, which is barely audible to the human ear.