Researchers studying elephants for clues to hearing impairment

ETOSHA NATIONAL PARK, Namibia — 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, 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.

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 behavior.

O'Connell-Rodwell 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. 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 of kilometers away, far beyond the reach of most airborne sound.

O'Connell-Rodwell knew a thing or two about vibrotactile sensitivity. Her master's thesis in entomology, done before the Africa trip, had examined how cicadalike Hawaiian planthoppers communicate using vibrations transmitted through their legs.

In 2000, working with a geophysicist, she published a scientific paper showing that elephant calls travel through the ground at a different rate than through air. (Precisely how far has not been documented in the field.) So the vibrations were there. The question was: Did other elephants perceive and respond to them?

Last year she reported that, yes, elephants can "listen" with their big, round feet, as vibrations travel up their legs and ultimately into their ears.

Now comes the latest twist. In August, the Journal of the Acoustical Society of America will detail her new findings that elephants can detect subtle frequency differences in vibrations and react accordingly.

For the study, she used recordings of two calls that had been made to warn of hunting lions. One was taped at Etosha, the other in faraway Kenya. They were played at the water hole at different times, using the ButtKicker to convey just the vibrations, stripped of the airborne sound.

"After the first experiment, I could see it was having an effect," she said, "but it took a long time to repeat it and get statistical evidence." With a local call, "the first thing they do is freeze; then they bunch up in the family unit, putting babies in the middle." Before long, the entire group would leave the water hole.

The Kenyan call had a less visible effect. Some elephants froze, but they did not bunch up or quickly leave the water hole.

Colleen Kinzley, the Oakland Zoo's curator and O'Connell-Rodwell's graduate student on the project, suggested that the local alarm might seem more real to the elephants, whereas the one from Kenya was akin to a foreign language.

To Kinzley, this fits in with what she has observed during elephant mating.

"We've seen males out here lean forward and clearly appear to use their body position to pick up vibrations," she said. "That's sometimes followed by females appearing or males leaving in a purposeful way."

At the zoo, Kinzley has trained an elephant named Donna to touch one sign when she feels a vibration and another when she does not. One aim is to see how far the vibration level can be turned down and have an elephant — at least a captive one — still feel it.

O'Connell-Rodwell said that when people lose their hearing, they lose it first at higher frequencies, meaning that a hearing-impaired person's ear is more sensitive to low frequencies, like an elephant's. The deaf are more sensitive to vibrations than those with normal hearing.

The science is complicated, but she speculates that lessons gleaned from elephants could, for example, enhance the results of cochlear implants in deaf babies. That explains her research post at Stanford Medical School's otolaryngology (ear, nose and throat) department.

She is no less excited about the possible benefits to conservation. Better ways of keeping elephants out of fields would help farmers and elephants.

To that end, her new research will explore whether an elephant's character influences how it reacts to vibrations. Once again using the ButtKicker, she will play the local alarm call in the presence of both a confident matriarch elephant, such as the aggressive one at Etosha that has been dubbed "Margaret Thatcher," and a more nervous matriarch.

At dusk, the team finished driving steel posts into the ground and wrapping a 10-foot-high bronze tarp around them. Later, they would add the electric fence.

It had been an eventful first day. A python was found curled up under one post. The rambunctious behavior of Brando and fellow bulls made everyone a bit nervous, with no quick escape available to the entire team. And just before sunset, as the perimeter was completed, a male lion roared his arrival at the water hole and lay down 150 yards from camp.

That night, O'Connell-Rodwell peered through a night-vision scope at the water hole. A football field away, more than 80 elephants cavorted and splashed. Occasionally, one rumbled like an idling tank or let out a trumpet burst. In the morning, her research would begin in earnest.