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Scientists report new
evidence that elephants communicate underground
Posted May 31, 2005
Courtesy Stanford University
and World Science staff
Scientists say preliminary findings from a new study seem to confirm
that elephants can communicate through underground signals.
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U.S. Fish & Wildlife Service
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The findings might explain reports that trained elephants in Thailand became agitated and fled from
the tsunami that killed more than 200,000 people in southeast Asia on Dec. 26. Their escape saved their
own lives and those of tourists riding on their backs.
The new findings come from ecologist Caitlin O’Connell-Rodwell of Stanford University in Stanford, Calif.
In 1997, she proposed that elephants
can communicate through deep calls that generate powerful ground vibrations known as seismic signals. Earthquakes and tsunamis
also spawn seismic signals. Elephants can feel the vibrations through their sensitive trunks and feet,
the ecologist hypothesized.
Seismic communication is common in small animals, including spiders and scorpions,
and has been found in elephant seals, which are unrelated to elephants. But O’Connell-Rodwell
is the first to have suggested that a large land animal could send and receive such messages.
She has proposed that the signals might be useful because they travel further
than airborne messages.
“Elephants may be able to sense the environment better than we realize,” she said, noting earlier studies showing that elephants sometimes move toward distant thunderstorms. “When it rains in Angola, elephants 100 miles away in Etosha National Park start to move north in search of
water,” possibly “sensing underground vibrations generated by thunder.”
Elephants may transmit signals as well as receive them, she added. But the transmissions aren’t necessarily
intentional: they could be byproducts of noises produced when elephants run, charge and sound off.
“Perhaps they’re sending out signals to potential mates far away,” she said. “Or maybe they can tell if a predator is in the vicinity by picking up seismic cues from a distressed herd.”
In the 1980s, scientists found that elephants emit a variety of infrasounds—calls too low to be heard by most humans—which other
pachyderms can detect more than two miles off. Scientists believe these long-distance communications are
vital for elephant survival, especially where they range over large areas.
Last July, O’Connell-Rodwell went to one such area, Etosha National Park in northern Namibia,
for an elaborate experiment to test for seismic signaling. At the park, more than 2,400 savanna elephants range over an area larger than El Salvador.
Her team set up camp at Mushara waterhole, a freshwater spring where elephants, giraffes, lions and other animals gather to drink or bathe during the dry Namibian summer.
The researchers spent a month performing tests designed to see how elephant herds respond when specific calls are played back through the ground.
The experiment was a followup on a simpler test of the same sort performed three years ago.
“Elephants live in matriarchal breeding herds made up of mothers, aunts and their offspring,” O’Connell-Rodwell
noted. “Once males reach puberty, around age 12, they get kicked out and start traveling alone or forming small bachelor herds.”
The search for a mate in this vast wilderness is further complicated by the elephant’s reproductive biology. Females breed when they are in
estrus, a brief ovulation period that occurs only every two years and lasts just a few days.
“Females in estrus make these very low, long calls that bulls home in on because it’s such a rare event,” O’Connell-Rodwell said.
The powerful calls carry more than two miles in the air and may be accompanied by long-distance seismic signals, she
added.
Breeding herds also use deep calls to warn of predators. Adult elephants have no enemies, except for humans, but young elephants are
vulnerable to lions and hyenas. When a predator appears, older members of the herd emit intense warning calls that prompt the rest
to clump together for protection and flee.
In 1994, O’Connell-Rodwell recorded the dramatic cries of a breeding herd threatened by lions at Mushara waterhole. “The elephants got really scared, and the matriarch made these very powerful warning calls, and then the herd took off screaming and trumpeting,” she recalls. “Since then, every time we’ve played that particular call at the waterhole, we get the same
response: the elephants take off.”
Reacting to a warning call played in the air is one thing, but what if the elephant could only feel the call through the ground?
To find out, the researchers used a device that converts acoustic sounds into vibrations. They buried
it near the waterhole in 2002 and connected it to a tape deck installed in an observation tower.
Every time a herd showed up at the waterhole, O’Connell-Rodwell would play a tape of the 1994 warning call, converted to a seismic vibration through the device.
The results showed “that elephants do indeed detect warning calls played through the ground,”
the ecologist said. As expected, the pachyderms clumped into tight groups and
left.
“But since we only played back one type of call, we can’t really say whether they were interpreting it
correctly,” she added. “Maybe they thought it was a vehicle or something strange instead of a predator warning.”
The 2004 experiment was designed to solve that problem by using three different
recordings: the 1994 warning call; a different sort of anti-predator call recorded in Kenya; and an artificial warbling tone. (Hear
actual elephant calls here.)
All three sounds were randomly played at different times to see if the elephants
would respond to each type differently. “We wanted to determine if they can discriminate between familiar and unfamiliar calls
that are played back as seismic signals,” O’Connell-Rodwell explains.
Although still analyzing results from the experiment, O’Connell-Rodwell made some preliminary
observations.
“The data I’ve seen so far suggest that the elephants were responding like I had expected. When the ‘94 warning call was played back, they tended to clump together and leave the water hole sooner. But what’s really interesting is that the unfamiliar anti-predator call from Kenya also caused them to clump up, get nervous and aggressively
rumble—but they didn’t necessarily leave. I didn’t think it was going to be that clear-cut.”
The findings could have implications for conservation, she added.
Human-generated noise may be a menace to elephant lifestyles, she explained. Researchers have found that
spinning helicopter blades generate low-pitched noises, and possibly seismic vibrations, that can disrupt and frighten wild herds located far away.
Some researchers argue, therefore, that helicopters in elephant-inhabited areas should be carefully monitored and controlled.
Seismic research also may prove useful against poachers. “There is military technology to detect and track tanks seismically,” said David Larom, an environmental scientist formerly with the University of California-San Diego and now in private industry. “This could potentially be used to track poacher vehicles as well.”
Eventually, O’Connell-Rodwell hopes to broaden her research to include other large animals that produce low-frequency vocalizations, such as rhinos, lions and giraffes.
“This is important basic
research,” Larom said. “Like all creatures, humans perceive with limited
spectra and sensory modes. We bias research with the unconscious and incorrect
assumption that other animals ‘see’ the world as we do. Every time we
discover otherwise, it expands the horizons of scientific knowledge and sends us
the humbling and vital message that we are not, after all, ‘the measure of all
things.’”
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