http://abcnews.go.com/wire/World/reuters20010312_3277.html
SAN FRANCISCO, March 12 (Reuters) - When an elephant puts its foot down,
people listen. And so, apparently, do other elephants -- using their toenails
to sense messages sent from as far as 20 miles (32 km) away. A new study by
Stanford University researchers indicates that elephants use foot-stomping
and vocal rumblings as part of an elaborate system of seismic communication,
sending vibrations through the ground to other elephants far beyond the reach
of audible sound. "If they are sensing these messages in the ground, it
radically changes our perspective how far they can communicate," Caitlin
O'Connell-Rodwell, a visiting scholar at the Stanford Center for Conservation
Biology said in an interview on Monday. "They may be communicating at far
greater distances than we thought." O'Connell-Rodwell's study, published in
the December issue of the Journal of the Acoustical Society of America, sheds
new light on how elephant herds transmit messages -- sensing greetings or
warnings of danger through their feet. By studying separate groups of
elephants in Africa, India, and in captivity in Texas, the Stanford
researcher found indications that elephants have a highly developed set of
seismic signals, creating ground vibrations both through their vocal calls,
which create a low level rumbling, and by stomping their feet in mock
charges. Other animals, ranging from certain types of moles and seals to
insects, fish, and reptiles, are known to use seismic signals to find mates,
locate prey or establish territories. But the elephants' methods of seismic
communication appear to be more complex, and travel far greater distances.
O'Connell-Rodwell said that the seismic waves created by various elephant
actions -- ranging from foot-stomping warnings to vocal calls of greeting --
were recreated and transmitted through the ground to see if elephants would
display the same reaction if no audible sound were present. "HEARING" WITH
THEIR TOENAILS The results showed that the elephants, particularly female
ones, picked up the signals and reacted. "We think they're sensing these
underground vibrations through heir feet," O'Connell-Rodwell said. "Seismic
waves could travel through their toenails to the ear via bone conduction, or
they may be using seismic sensitivity in their trunk. It may be a combination
of both." Earlier elephant studies have shown that they can produce low-level
20 hertz vocal rumblings which can travel up to six miles (10 km) through the
air under ideal conditions. Subsequent studies showed that these rumblings
themselves create a seismic "echo" in the earth, where the vibrations travel
even greater distances. These vibrations are also created by the
foot-stomping and ear flapping of mock elephant charges, which the animals
use as a defense mechanism when danger is perceived. "Based on our
mathematical models, we estimate that seismic signals produced by elephants
can travel between 10 and 20 miles (16 - 32 km) in the ground,"
O'Connell-Rodwell said. She added that current evidence indicated that
seismic signals conveyed basic information about where elephants are and what
their mood is -- enabling elephants at some distance to sense fear or anger.
"Whether or not they can discriminate individuals in the ground is something
that we are trying to do in the future with more studies," O'Connell-Rodwell
said. Already, observation of elephant behavior in Angola hinted that seismic
signals may travel even farther, with thirsty elephant herds there detecting
and moving toward thunderstorms as far as 100 miles (160 km) away.
O'Connell-Rodwell said evidence of seismic communication was found in both
Asian and African elephants, and could lead to a far broader understanding of
how all sorts of animals communicate in the wild. "It really opens the door
to (seismic communication among) other mammals," O'Connell-Rodwell said. "We
picked the one animal that was the most obvious -- because elephants are so
large, and so heavy. But are also looking for this possibility in rhinos,
possibly in bison, and possibly in lions," she said. (San Francisco bureau,
415-677-2541, andrew.quinn+reuters.com)