The huge bull elephant nicknamed "Marlon Brando" loped over to the water hole, big ears flapping in the breeze. Soon he and four massive bull underlings indulged in a spirited bath that darkened their gray girth.

Buried in the sandy soil nearby, switched off at the moment, sat a device probably never before known in this remote stretch of southwest African wilderness: the same kind of ButtKicker subwoofer that gives many American home theaters their bone-rattling shake.

Here in the Etosha National Park in Namibia, the device has led to groundbreaking discoveries about how Brando and his kind communicate. Not only can elephants find meaning in calls that pulse through the ground as vibrations, says Stanford ecologist Caitlin O'Connell-Rodwell, but a new study shows that they can tell whether the source is familiar or foreign.

It has been likened to a caller ID system and could have implications for humans. The benefits could one day include insights into hearing impairments and new ways to stop elephants from devouring the crops of subsistence farmers across Africa.

Thunder in the ground

O'Connell-Rodwell, 42, hopes to learn much more about this mysterious seismic chatter, possibly explaining behavior that has long been observed but is not well understood.

"Elephants are the first to move to rain," she noted. "We think they may be tuning in to thunder in the ground."

After gazing out at Brando and the boys, she rejoined her assistants as they raced the sun to set up camp for a fresh season of research. For five weeks, home will be a 13- by 13-yard enclosure surrounded by electric fencing to ward off lions.

A three-level platform offers commanding views of the water hole 90 yards away, and a concrete bunker allows close observation. The ButtKicker will be fired up for vibration experiments - but it will be used sparingly, to minimize disrupting the animals' behavior. O'Connell-Rodwell also will study bull elephant social interactions.

She has been visiting this water hole off and on since 1992, when she stumbled into a career of elephant study. She and her husband, Tim Rodwell, had embarked on a nine-month backpacking trip across Africa between college degrees. They never got past Etosha. Days after they agreed to volunteer for a while, the park's head of research offered them a three-year paid assignment studying elephant migration in the Caprivi Strip. They jumped at the chance.

A big issue there, as elsewhere, was crop damage by elephants. She experimented with car alarms as a scare tactic and saw results. But she thought using elephants' own alarm calls would prove more effective.

She experimented with audio recordings at Etosha in the mid-1990s. Elephants responded more to elephant sounds taped near their home turf. When they heard a local alarm call, "they would just take off." When it was from another area, "they'd leave, but wouldn't run away immediately."

Working toward her doctorate at the University of California, Davis, she set out to test a hypothesis that elephants could detect signals through the ground. She suspected that they could, based on observations at Etosha.

Even in what sounded to human ears like absolute silence, elephants would suddenly freeze, lean forward, press down hard on a front foot and focus on the ground. Rather than waving their ears to catch sounds, they plastered them against their heads. Sometimes they did this well before another herd would arrive from a couple kilometers away, far beyond the reach of most airborne sound.

Listening with their feet

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