Since the 1980s, people have known that elephants communicate with each other using infrasound - noises pitched too low for the human ear to detect them. Last year an unlikely alliance consisting of an ecologist, an epidemiologist, a zoo curator, a geoscientist, a vet student and a law student set up camp in Namibia to further investigate elephant communication.The research, led by ecologist Caitlin O'Connell-Rodwell, is conclusively proving that elephants also use seismic vibrations in the ground to communicate. The elephants are thought to detect the minute vibrations through special nerve cells in their trunks and feet. Elephants' ability to sense seismic signals was brought to public attention when trained elephants in Thailand moved to higher ground just before last year's tsunami struck, saving themselves and their tourist passengers.O'Connell-Rodwell has returned to Etosha this year to continue her investigations into elephants' seismic senses, relates Melissa Groo of Save the Elephants. The team developed special apparatus that would convert audible elephant calls into vibrations in the soil. A recording made in 1994 of the alarm calls of a breeding herd of elephants confronted by lions was used. When played through loudspeakers, the recording disturbed other elephants, causing them to leave a waterhole. The same call was wired up to a buried ground shaker, and played only through the ground.Above ground microphones ensured the call was not audible in the air. The seismic vibrations had the same effect on elephants visiting the waterhole that the audible call did - they clustered together and left in a hurry. After the initial success of this experiment, the team used two other calls to test elephant responses. The initial alarm call was recorded at the same waterhole in Namibia where it was played back, so a second alarm call was recorded in Kenya. The third call used was an artificial warble.Analysis of the findings is still underway, but O'Connell-Rodwell says, "The data I've seen so far suggest that the elephants were responding like I had expected. When the '94 warning call was played back, they tended to clump together and leave the waterhole sooner. But what's really interesting is that the unfamiliar anti-predator call from Kenya also caused them to clump up, get nervous and aggressively rumble - but they didn't necessarily leave. I didn't think it was going to be that clear cut." O'Connell-Rodwell is further expanding her research with a new study on how calls made by cows in oestrus affect the dominance hierarchy amongst bulls.Other than finding out more about how elephants communicate, the experiment is also hoping to develop a remote sensing technique for counting elephants and other animals using geophone arrays. Geophones detect seismic waves in the ground. "Our work is really at the interface of geophysics, neurophysiology and ecology. We're asking questions that no one has really dealt with before."