AR-News: Elephants might be "talking" via seismic waves, scientists say

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Posted on Tue, Jun. 22, 2004    
    
    
    Elephants might be 'talking' via seismic waves, scientists say


By Betsy Mason

CONTRA COSTA TIMES


Elephants may keep their ears to the ground by using their feet. Stanford 
scientists think the animals communicate through ground vibrations.

African elephants depend on being able to communicate over long distances 
using calls that are below the range of human hearing. These low-frequency 
"rumbles" can travel several miles through the air, helping different elephant 
families coordinate their movements from afar and occasionally meet up with each 
other. Elephants' jumbo-size ears are designed to capture these calls.

But big ears may not be the only special equipment elephants use to pick up 
their friends' calls. A group of scientists at Stanford University suspects 
that the rumbles cause seismic vibrations that the pachyderms can feel in their 
feet. The team has turned to a specially trained elephant at the Oakland Zoo to 
help them figure out exactly what the animals can sense.

"People are really fascinated with the idea, because it explains a lot of 
things they see in the field," said biologist Caitlin O'Connell-Rodwell, the 
leader of the Stanford team.

She first guessed that elephants might be "listening" to vibrations in the 
ground more than a decade ago while working for the Namibian government to try 
to help farmers keep elephants from trampling their fields. She noticed that 
groups of elephants would sometimes freeze in their tracks in unison and stand 
still for a short time.

Other scientists have seen this pattern as well, and usually the animals are 
spreading their ears to scan for distant calls. But O'Connell-Rodwell observed 
them freezing without scanning, and suspected they might be feeling ground 
vibrations. The elephants would also often lift one of their legs, perhaps to 
press the remaining three into the ground for a better feel. This strange 
behavior would often be followed later by the arrival of another group of elephants.

O'Connell-Rodwell teamed with Stanford geophysicist Simon Klemperer to see if 
the rumbles really do create seismic waves in the ground. The pair, along 
with Stanford undergraduate Roland Günther, placed geophones, devices that 
measure and record vibrations, in the ground near Salinas.

They then recorded the rumbles made by a trained male elephant when he was 
reunited with his female companions after a three-hour separation and discovered 
that the calls make distinctive ground vibrations that move along the surface 
of the earth.

"It's like a water wave on the ocean," Klemperer said. "It's trapped at the 
surface." This could give the ground waves an advantage over sound waves 
traveling through the air. Airborne sound moves away from its source in all 
directions, like an expanding sphere away from a burst balloon, and energy is lost 
along the entire surface of the sphere as it grows.

But surface waves in the ground move from their source in a circle or very 
shallow cylinder, like ripples rolling away from a pebble dropped into a still 
pond, with much less surface area for energy loss. "So in theory, the seismic 
signals have the capacity to travel much further than airborne sound," said 
O'Connell-Rodwell.

In reality, under normal conditions, the airborne sound is likely to travel 
as far and probably farther than the ground waves.

Acoustic biologist Katy Payne of Cornell University, who was the first to 
discover that elephants were using these low rumbles that humans can't hear, has 
found that the sound may travel as far as 2.5 miles through the air. And 
according to the Stanford study, the ground waves aren't likely to travel more than 
half that distance in the energy-sapping sandy terrain that covers most of 
the elephants' range in Africa.

Still, O'Connell-Rodwell thinks that under some conditions the ground 
vibrations could win out, and Payne agrees. "On a very windy day, when it's very 
noisy, it might be that seismic communication would work better," Payne said.

The wind, too, creates "noise" in the ground, but elephant calls have a 
characteristic vibration that the animals may be able to filter out, just as people 
can pick out their own names spoken from across the room at a noisy cocktail 
party.

But do elephants actually feel and recognize the vibrations? Nobody knows 
yet, but the team is working on this question with Colleen Kinzley, general 
curator at the Oakland Zoo, and Donna, a 25-year-old African elephant.

The scientists attached a large metal plate on the ground to a device 
affectionately called a "butt-kicker shaker" that can create vibrations that mimic 
elephant rumbles and other sounds. Kinzley trained Donna to stand on the plate 
and touch a green square if she felt a vibration, or a silver triangle if she 
didn't.

They did the experiment first with both sound and vibrations to be sure Donna 
understood the task. When they took away the sound and just vibrated the 
plate, she still got the answers right.

"This is the first time we've ever trained an elephant to participate in a 
study where they are answering a question," Kinzley said.

And, although Donna has become frustrated with the experiment at times and 
tried to tear up the wires connecting the shaker to the plate, for the most part 
she has really enjoyed it, Kinzley said. "Donna's a real patient elephant. 
She's real smart and likes to participate in things."

Next they plan to see if Donna can distinguish between different types of 
elephant calls, such as warning rumbles and greeting rumbles.

O'Connell-Rodwell and her group are also studying wild elephants in Namibia. 
In the past, the elephants have reacted to warning rumble vibrations played to 
them. Now, the team is back in Africa to see if the wild elephants respond 
differently to different call vibrations. Kinzley is planning to join them in 
Africa to help interpret the elephants' behavior.

In the future, O'Connell-Rodwell hopes to figure out how the elephants might 
perceive the seismic waves. One theory is that they have special sensors in 
their feet. Another is that their feet are shaped to act like drums that amplify 
the vibrations, which then travel through the elephants bones and into their 
ears.

However they do it, elephants are likely to use every possible resource to 
keep in touch with each other since long-distance communication is often the 
only way solitary males and herds of females can find each other to mate. So when 
finding one another at the right moment is critical, maybe a few vibrations 
will help.

    


 
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