Few sights in nature are as awesome as a 6-ton elephant guarding her baby from a hungry predator.
Rather than retreat, the threatened mother is likely to launch a mock charge - a terrifying display of ground stomping, ear flapping and frantic screaming designed to frighten off lions and hyenas.
But elephant researchers have discovered that there is more to a mock charge than meets the eye - or the ear, for that matter. It turns out that foot stomping and low-frequency rumbling also generate seismic waves in the ground that can travel nearly 20 miles along the surface of the Earth, according to a new study in the Journal of the Acoustical Society of America (JASA).
More astonishing is the discovery that elephants may be able to sense these vibrations through their feet and interpret them as warning signals of a distant danger.
"Elephants may be able to detect stress from a herd many miles away," says Caitlin O`Connell-Rodwell, an affiliate of the Stanford Center for Conservation Biology and a postdoctoral fellow in the Department of Pediatrics.
"They may be communicating at much farther distances than we thought," adds O`Connell-Rodwell, author of the JASA study.
To test the theory that elephants transmit and receive underground messages, O`Connell-Rodwell and her colleagues previously conducted several novel experiments with pachyderms in Africa, India and at a captive elephant facility in Texas.
"We went to Etosha National Park in Namibia and recorded three acoustic calls commonly made by wild African elephants," she says. "One is a warning call, another is a greeting and the third is the elephant equivalent of `Let`s go!"`
The researchers wanted to find out if elephants would respond to recordings played through the ground, so they installed seismic transmitters at a tourist facility in Zimbabwe where eight trained, young elephants were housed.