Elephant Eavesdropper Comes to Town

Silent ThunderNASHVILLE, Tenn. (June 18, 2001)

The Elephant Sanctuary of Hohenwald, Tenn., in conjunction with the Zeitgeist Gallery, hosted noted researcher, author, educator and lecturer Katherine Payne. Payne was in Nashville to speak about "Silent Thunder: In the Presence of Elephants," her book on elephant communication tools at the Zeitgeist Gallery in Hillsboro Village.

Katy Payne and her team of researchers conducted non-invasive research at the Sanctuary June 21-24, 2001. Bruce Thompson and Mya Thompson are the principal investigators in the seismic work. They have collected and will now spend endless hours evaluating the data. Bruce is a professor at Ithaca College. Mya works close with Katy in the Elephant Listening Project. An important adjunct to the equipment brought by the researchers was the Sanctuary's on-site remote observation cameras. These cameras allowed the researchers to record, during daylight hours, where each elephant was, so as to attribute any elephant calls recorded to the appropriate elephant. Their "Elephant Listening Project" continues to uncover the communications between individuals as well as herds of elephants. The information that Katy and her team gather may help provide a solution to the human elephant conflict that threatens populations of wild elephants.

Four custom designed audio recording units (ARU) were placed high in trees in the elephants' habitat. Continually for the next three days and nights these devices collected and stored elephant vocalizations. Additional listening devices, designed to record vocalizations not audible to the ARUs, also collected vocalizations over the three day period.

All of the information collected will be compiled and studied to further the teams understanding of the different ways elephants communicate with each other over great distances.

Katy watching Eric prepare the ARU
Katy watches Eric prepare the ARU

Katy and Maya making final adjustments
Katy and Maya making final adjustments

Scott putting the ARU in tree
Scott putting the ARU in tree
(Scott is in the tree and Bruce and Eric are assisting from the ground)

Melissa and Bruce identifying ARU's exact position
Melissa and Bruce identifying the ARU's exact position
with the aid of the Global Position Satellite.


Both Sanctuary staff and the research team shared experiences and video of their time spent with elephants. All were encouraged by the many similarities between the behavior of wild elephants and the behavior of the captive elephants living at the Sanctuary. The on-going relationship between these two like minded groups will most definitely prove to bring a greater understanding of the way elephants think and communicate, undoubtedly furthering the understanding and welfare of both wild and captive elephants.

Payne spent more than a decade in the field researching African elephants and their acoustic behavior. In addition to "Silent Thunder: In the Presence of Elephants," Payne wrote a children's book "Elephants Calling," and currently is a research associate at Cornell Laboratory of Ornithology in Ithaca, NY.

Links to Internet Resources for Seismic Communication by Elephants

Rumble in the Jungle - Joanna Marchant, New Scientist, August 4, 2001

"The Elephant Listening Project"

"Eavesdropping on Secrets of Elephant Society" by Andrew Revkin, New York Times, January 9. 2001



Melissa Groo
Save the Elephants News Service Researcher

Rumble in the Jungle
Joanna Marchant
New Scientist
Aug 4, 2001

For elephants, long-distance communication could be a matter of feeling the vibes. Joanna Marchant puts her ear to the ground.

ELEPHANTS have mysterious powers. A thunderstorm in Angola prompts animals in Namibia to move north in search of water. A large elephant cull leaves another herd 50 kilometres away tense and agitated. They must be picking up signals somehow. Hearing or smelling events at such long range is out of the question, so what's going on?

Zoologist Lynette Hart thinks she has the answer. She is convinced that elephants can talk to each other through the ground. That would make them the only large terrestrial mammal we know that communicates using seismic signals. Now Hart and her colleagues are starting to piece together the evidence. But elephants can be a subtle and elusive bunch-and watching them in action provides many surprises.

The first real clue that the animals might be sensing distant vibrations came in 1992 when Caitlin O'Connell-Rodwell noticed some elephants in Namibia acting strangely. "They would freeze, lean forwards, and lift up one foot," says O'Connell-Rodwell, who was then a student of Hart's at the University of California in Davis.

She felt the elephants' behaviour was strangely familiar, and realised that she'd previously seen insects doing the same thing when they were feeling for rumblings. "If they lift one leg up, they get better coupling to the ground with the other three legs." But what might the animals be listening to? When O'Connell-Rodwell returned to the US, she told Hart about the enigmatic behaviour she had seen. Intrigued, Hart talked it over with her brother, geophysicist Byron Arnason. They wondered whether the elephants were using seismic waves to carry their calls through the ground. "She'd been talking about the possibility for a long time," says Arnason. "I was involved in oilfield seismic exploration, looking for oil. Our minds melded together."

Thanks to Arnason's expertise with seismic waves, they knew that some elephant calls had the necessary characteristics to travel efficiently through the earth. They have frequencies as low as 20 hertz, and they are loud. So Arnason temporarily stopped looking for oil, gathered up his monitoring equipment, and set off with the others to an elephant sanctuary in Texas to listen in.

To test for vibrations, Arnason placed microphones 10 metres from the elephants and also further away, at around 45 metres. Directly beneath each microphone he buried a geophone, which measures ground vibration. Sound travels at a different speed through earth than through air, so this would show whether calls were being carried in the ground independently of those in the air. "We had to measure both the acoustic and seismic signals to show that they arrived at different times," says Arnason.

The results, published in The Journal of the Acoustical Society of America (vol 108, p 3066), showed exactly that. What's more, by measuring the rate at which they faded, the researchers also worked out that sounds travelled much farther through the ground than through the air. They estimate that elephant calls could travel around 16 kilometres through the ground. Vibrations caused by mock charges-the sort of crashing around that elephants do when they are nervous or afraid-might travel even farther, up to 32 kilometres. By contrast, calls can't be heard more than about 10 kilometres away.

Why would elephants need these long-range seismic signals? "The communication is for coordination within and between herds of closely related individuals," says O'Connell-Rodwell, who is now at Stanford University. "The herds move in the same direction, even though they are not in eye contact." Elephants roam over vast areas and seismic communication would extend the range over which they could stay in touch.

But how might the animals pick up the seismic signals? One possible answer came from a surprising quarter. When the researchers mentioned their ideas to Bets Rasmussen, an expert in elephant chemical communication from the Oregon Graduate Institute of Science and Technology, she had no doubts. "I know they can do this with their trunks," was her response.

Rasmussen's conviction came from her work in India, investigating how elephants use their highly developed sense of smell. Pheromones that signal sexual status are particularly important, and elephants detect them using a specialised organ in the roof of their mouths. Rasmussen wondered whether the tip of the trunk also had chemical receptors in it. But when she searched the literature she was amazed to find that nobody had ever studied the trunk tip. "In some parts of South-East Asia, the tip is considered sacred," she says. "People cut it off and keep it as a good-luck charm. So when an elephant dies that is the first bit to go-the scientists never get their hands on it."

To plug the knowledge gap, Rasmussen enlisted the help of anatomist Bryce Munger from the University of Tasmania, who had previously studied the anatomy of monkey snouts. "He was about to retire, but I convinced him to do this one last project," she says. "Then he called me up and said, 'You wouldn't believe it!'" The trunk tip was the most sensitive tissue Munger had ever seen.

But it wasn't picking up chemical signals. Instead, Munger found specialised cells called Pacinian corpuscles which pick up vibrations. They comprise concentric membranes of connective tissue, like the layers of an onion, with the gaps between filled by a slimy gel. Movements or vibrations deform the layers, sending a nerve signal to the brain. These corpuscles are found in other mammals too, in human fingertips, for example, but in the elephant trunk they are particularly densely packed. "They would definitely make it possible for elephants to detect low-frequency vibrations in their trunk tip," says Rasmussen.

The finding explains stories about elephants laying their trunks on water pumps, as if to see whether they are switched on or not. But O'Connell-Rodwell and Hart were convinced this couldn't be the whole story. What about that strange foot-lifting behaviour they had observed? Surely it must hold another clue. "Elephants have extraordinary feet," says Hart. "They stand on their toes. Their toes rest on this big gooey ball of fatty tissue. It feels like a waterbed." That's why you never hear an elephant walking, she adds. Hart plans to dissect elephant feet to see if she can find the same vibration-sensitive cells that Munger found in the trunk. Vibrations in the ground would make the dense fatty cushion of the foot undulate, stimulating any Pacinian corpuscles within.

The idea that elephants are sensing the world through the soles of their feet has got other researchers in the field talking. "People are really excited," says O'Connell-Rodwell. "It answers a lot of mysterious questions for them about what elephants do in the wild." For example, Iain Douglas-Hamilton, founder of the Nairobi-based conservation group Save the Elephants, says the notion would explain one strange habit he has witnessed. When elephants come across a dead elephant, he says, they touch the body very delicately with their feet, as if checking whether the animal is alive by looking for vibrations in the body. "I get the feeling that they use the foot as a sensory organ," he says. "They are like large plate-like scanners."

O'Connell-Rodwell and Hart say that if elephants are also sending messages through the ground deliberately, rather than simply sensing information, the messages are probably quite simple-more "I am here, where are you?" than "Come down to the waterhole, there's a party on Friday night". That's because the signals travelling through the ground are very plain. "The seismic signal has virtually no modification on it at all," says Arnason. "So if they do communicate seismically, there's very little information they can put in. The only specific characteristics are duration and frequency."

Arnason points out that it would be impossible for elephants to transmit complex information through seismic signals, because any details would get garbled. "When you propagate a pulse through the ground using surface waves, it becomes very distorted," he says. And if you analyse elephant calls you find that the high pitched ones such as trumpeting, which could not travel through the ground, tend to carry more detailed information than lower pitched ones. That fits with the idea that elephants intend some calls to travel seismically.

Even without complex signals, elephants might be able to work out how far away the caller is by comparing the arrival time of the signal in the air with that in the ground. They could also tell the direction from which the call came, depending on which foot felt it first, says Arnason.

The details of how elephants analyse sound signals remains a mystery. What is clear is that they have plenty of brain power with which to do the complex information processing involved. In work soon to be published in Animal Behaviour, Hart compared the brains of different sized mammals, and calculated how much of the brain would be required simply to run the body. "The Asian elephant has more cortex to spare than any other mammal," she says. "They have a tremendous amount of brain power. Maybe they could use it to integrate all this information coming from their trunk and feet."

In addition to detecting specific calls, elephants would also be able to use their seismic sense to glean information about distant events. O'Connell-Rodwell believes they might be able to tell what mood another group was in, from how often they called, for example, or by sensing any agitated mock charges. "If they can sense a herd running away from a waterhole, then they might guess there are lions there," she says.

Then there are culls. "There's anecdotal evidence that when you have large elephant culls, other herds are able to sense it 50 kilometres away," says Arnason. That's too far for the animals to be hearing or smelling anything, but they could be picking up the vibrations from the helicopters used by the hunters, or from stampeding herds.

Another mystery is how elephants seem to sense distant thunderstorms. "When it rains in Angola, elephants 150 kilometres away in Etosha start to move north in search of water," says O'Connell-Rodwell. "They shouldn't be able to hear it," says Arnason. He's now investigating whether it would be possible for elephants to pick up seismic waves caused by thunder so far away.

Arnason even speculates that sensing thunderstorms could have been the original reason why elephants evolved the ability to detect vibrations. "In Central Africa, what was the ambient seismic noise 10,000 years ago? It was thunderstorms. And water would have been very important to the elephants. Maybe first they were able to sense the vibrations, and then found out they could generate them too," he says.

But so far the evidence is circumstantial. To prove their theory, Hart and her colleagues need to show that the elephants can respond to the vibrations set up by their calls, something that's easier said than done. "They are very subtle animals," says Hart. "They don't necessarily respond in a constant way." They might orient towards the source of the sound, shift their weight, freeze, hold their ears out, or do nothing at all. "If they don't respond they may still be hearing it, just not interested," says Katy Payne, of the Elephant Listening Project at Cornell University in New York. Payne says she likes the seismic theory.

Hart and O'Connell-Rodwell have already carried out one study where they recorded three common acoustic calls-a warning call, a greeting call, and the elephant equivalent of "let's go!" They played the calls back through seismic transmitters to eight young, domesticated elephants in Zimbabwe. "We made sure the elephants were only feeling the seismic stimulation," says Hart. They compared the elephants' responses to the calls with their responses to vibrations derived from synthesised tones, rock music and to silence.

The seven males were blasé. "At first we thought they weren't responding, and we got disheartened, but the trainers would say they are responding, they're just pretending not to!" says Hart. Certainly, one female became very agitated when the "warning" signal was played, even biting the ground-a behaviour only seen in elephants under extreme stress. The researchers videotaped the elephants' responses and are now using computer analysis to try to pick out more subtle changes in the elephants' behaviour.

In the meantime, they are planning a further round of tests due to start in October, in which they will train elephants at a nearby zoo to respond to certain sound signals in a specific way. "Once the elephant senses the thing that it has been trained to respond to, it touches its trunk to a target," says O'Connell-Rodwell. The researchers then plan to play seismic versions of the calls, to see whether the elephants still respond. They hope the project will provide definitive evidence for their theory.

But if elephants can pick up seismic signals, vibrations caused by human activity could now be interfering with or preventing this ability. "Anywhere near a town has gigantic amounts of background seismic noise," says Arnason. Even out in the desert, his equipment still senses trucks passing up to 30 kilometres away.

Remote areas of Africa and India aren't immune either-low-tech devices such as water pumps create vibrations too, and aircraft noise permeates everywhere. "The amount of seismic noise that transcontinental jets produce is enormous," says Arnason. "When a jet comes towards you it's not such a problem, but once it passes you, there's a large Doppler shift." This moves the high frequencies of aeroplane noise down into just the range that elephants use.

Hart fears that sound pollution could be very damaging. "Seismic vibrations from human activities may limit elephants' access to information. It may be disruptive to their social activities, and it may be stressful to them," she says. "The kind of environment in which animals evolved these sensibilities no longer exists."

Joanna Marchant
From New Scientist magazine, vol 171 issue 2302,
04/08/2001, page 28