Caller ID in the wild: African elephants communicate by ground vibration, Stanford researcher finds

STANFORD, Calif. - In the vast expanse of African grasslands, wild herds of migrating elephants have learned to communicate with each other by listening with their feet to vibrations in the ground. Now a Stanford University School of Medicine researcher has found their seismic communication system is so sophisticated the elephants have their own version of "caller ID."

"It's a much richer communication system than we thought," said Caitlin O'Connell-Rodwell, PhD, an ecologist who initially discovered this underground communication system 14 years ago while observing wild elephant herds in northern Namibia.

O'Connell-Rodwell has written about this journey of scientific discovery in her book, The Elephant's Secret Sense: The Hidden Life of the Wild Herds of Africa, published in March. Her newest study on the topic, which measures the ability of elephants to recognize whether an underground message is delivered by a familiar or unfamiliar source, will be published in August in the Journal of the Acoustical Society of America.

"I see this is going to be a lifetime journey," said O'Connell-Rodwell, a research associate in the school's otolaryngology department. She hopes to draw analogies between humans and elephants in research conducted with people and hearing implants at Stanford because the hearing-impaired population is "much better at feeling vibrations," she said.

O'Connell-Rodwell's journey into discovering this secret sense of elephants began with a simple observation. While hunkered down in a bunker observing family herds of elephants next to a favorite watering hole at Etoshia National Park in northern Namibia in 1992, she noticed a curious behavior. Suddenly the entire herd would freeze, ears flattened to their heads. Each enormous beast would lean forward up on tiptoes, sometimes raising one foot in the air.

Credit: Max Salomon Caitlin O'Connell-Rodwell

Caitlin O'Connell-Rodwell

"When elephants are listening with their ears, they have huge, extended ears," O'Connell-Rodwell said. But in this instance, the ears remained flat. She knew about the process of listening through limbs, a phenomenon known as "seismic communication" in insects, having spent endless hours in a small soundproof chamber recording the seismic love songs of Hawaiian planthoppers when she worked toward a master's degree in entomology. O'Connell-Rodwell became convinced the elephants were listening to seismic vibrations through the earth, but it's taken her years of painstaking scientific research to convince the rest of the world.

"It took a long time for this idea to gain momentum," said O'Connell-Rodwell, who also works with her husband Tim Rodwell in San Diego to co-direct a nonprofit conservation organization, Utopia Scientific. "People weren't thinking that larger mammals could do this. We've had to prove ourselves each step of the way."

Past studies by O'Connell-Rodwell and colleagues have shown that when African elephants stomp and rumble as a predator approaches, other distant elephants can get the news by feeling the ground ripple through their feet or trunk. This may have the direct or indirect effect of alerting other elephants of potential predators and other threats. Other seismic messages, such as distance thunder rumblings, could also let elephants know when and where the rains will arrive, explaining their uncanny ability to move hundreds of kilometers in the right direction to get to the green growth that the rains will bring.

The new study suggests that not only can the elephants receive and interpret underground calls, but they can distinguish between specific callers.

Working with senior author Sunil Puria, PhD, Stanford consulting associate professor of mechanical engineering, to conduct the study, O'Connell-Rodwell and colleagues converted previously recorded alarm calls from two different elephant herds into seismic vibrations and sent them to a herd of elephants at the watering hole at Etosha National Park. The recorded alarm calls were very similar, both low-frequency vocalizations that lions were approaching, but one was sent by elephants living in the same park as the study group in Etosha, and the other taken from elephants living far away in Kenya.

"The elephants at the watering hole responded only to the familiar calls," O'Connell-Rodwell said. "They would freeze, clump into tighter groups, leave the watering hole earlier. I expected some response to the unfamiliar calls, but they didn't appear to care about it at all.

"I wasn't expecting their ability to be that subtle," she said. "Maybe I underestimated it."

O'Connell-Rodwell has spent most of her summer months for the past 14 years hidden in the same dank bunker watching the same group of migrating elephants at the watering hole in Etosha National Park. Over the years, she's been stalked by lions who have climbed up on the bumper of her pickup truck when she was sleeping in the back and, once, nearly climbed headlong into her bunker. Still, she writes about her bunker and her herd of elephants with continuing appreciation and awe.

"The bunker is wonderful," said O'Connell-Rodwell, who camped out alone for weeks at a time patiently observing the elephants' behavior. She loved "listening to the night sounds, the lions roaring, the hyenas calling."

Her wonder at these enormous beasts of Africa fills her book. She writes about the "tiptoeing elephants" with their "vaudeville eyelashes almost comical in length" and "giant stethoscope feet" with love and admiration.

"We still have this very special window into their society but I don't know for how much longer," O'Connell-Rodwell said. "I grew to understand the elephant's society. How they treat each other. How they care for each other. I watched their relationships."

She grew to know which of the elephant bulls were the bullies, which the gentle giants. She even named them. One bull with a long, scraggly, gray tail, dubbed "Willy Nelson," is "a little bit of an outsider, but well-respected," she said. One of the matriarchs dubbed "Margaret Thatcher" is "somewhat of a tyrant but takes care of her own."

O'Connell-Rodwell's passion for elephants began all those years ago, with an initial serendipitous job offer. During a nine-month trip to Africa with her husband, she was offered a job helping Namibian farmers come up with new ideas for scaring away rampaging, wild elephants that could devour a year's worth of crops in one day. She's still working on new ideas as the elephants continually adapt to her plans to scare them off with car alarms or underground warnings.

"They're just too freakin' smart," she said.

She'll be heading back to Africa once again on June 8 for two months of elephant observation.

O'Connell-Rodwell works with principal investigator Robert Jackler, MD, professor and chair of otolaryngology. She has received funding for her elephant studies from the National Geographic Society, the U.S. Fish and Wildlife Service, the National Science Foundation, the Seaver Institute, TRAFFIC International and several Stanford University grants including including one Bio-X award with co-principal investigators Simon Klemperer, PhD, professor of geophysics, and Robert Sapolsky, PhD, professor of biological sciences and of neurology and neurological sciences.



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