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Elephants "Hear" Warnings With Their Feet, Study Confirms

John Roach
for National Geographic News
February 16, 2006
 
When African elephants stomp and trumpet as a predator approaches, other
distant elephants can get the news by feeling the ground rumble, a team
of scientists recently confirmed.

The vocalizations and foot stomps resonate at a frequency that elephants can detect in the ground, according to Caitlin O'Connell-Rodwell, a biologist at Stanford University in Palo Alto, California.

She and her colleagues played the ground-shaking component of these vocalizations to elephants gathered around a watering hole in Etosha National Park in Namibia (map).

"What we saw was they bunch into a tighter group, orient in the direction of where the signal is coming from, and then leave the area much sooner than they would if nothing was played," O'Connell-Rodwell said.

These behaviors are indications that the elephants detected the call and interpreted it as a warning, she added.

O'Connell-Rodwell and her colleagues reported the finding this month in the online edition of the journal Behavioral Ecology and Sociobiology.

O'Connell-Rodwell first theorized that elephants use vibrations to communicate in 1992, but this is the first scientific evidence to support her theory. (Read "Elephants May 'Talk' Via Vibrations")

Peter Narins, a biologist at the University of California, Los Angeles, says he's pleased to see her theory validated by a scientific study.

"She's shown it before, but this is real. The data are here, the controls are here, and it's been collected in a study," he said.

Now O'Connell-Rodwell and colleagues are preparing a follow-up report on whether the elephants can distinguish different types of calls.

Preliminary results suggest that elephants react most vigilantly to familiar warning calls, but they also crowd together and act nervous when they detect unfamiliar calls.

Vibration Threshold

UCLA's Narins says animals use "multiple mechanisms" to detect seismic vibrations.

For example, the African desert golden moles that he studies have extremely large bones in their ears that can detect low-frequency vibrations made by dune grass blowing in the wind. The dune grass sits over mounds where the moles' insect prey reside.

O'Connell-Rodwell says elephants have similar enlarged ear bones, so they may use the same mechanism to detect vibrations.

The scientist also believes that pressure-sensitive nerve endings in the elephants' feet and trunks are other pathways for detecting the vibrations of distant elephants.

But how sensitive are the elephants to these seismic signals?

O'Connell-Rodwell is currently exposing a captive elephant at the Oakland Zoo in California to lower and lower levels of vibration to determine the answer. (See a video of Donna, an elephant at the Oakland Zoo, demonstrating how she can "hear" with her feet.)

"What's the lowest threshold she can detect? … She is focusing and getting better and better at doing the task [of sensing the motion]," O'Connell-Rodwell said.

"Just when we thought we had reached the threshold, she's now learned and is doing better."

The learning curve suggests that the elephant had previously filtered out the seismic environment as noise. Now that she understands the task, she is focusing more attention to it, O'Connell-Rodwell said.

Conservation Implications

O'Connell-Rodwell says her research indicates how important the seismic environment is to elephant communication. This knowledge may in turn help conservation efforts, she adds.

For example, she says she would like to see land managers consider the seismic environment when they decide where to draw park and nature reserve boundaries to ensure that elephants can communicate.

O'Connell-Rodwell and her colleagues have also begun to study the nuances of elephant signals to distinguish them from the footsteps of rhinoceroses or lions.

"We're developing a [vibration-based] census technique that can count the number of elephants versus other large mammals that come to a water hole," she said.

In theory, researchers could leave their equipment at a water hole to record data for months at a time. The equipment could also be used in dense forests where it is difficult to count elephants from the air.

The researchers also hope to teach park rangers how to identify the telltale rumble of a vehicle in the wrong place at the wrong time—like a car full of poachers near an elephant herd.

"Managers would know whether or not a vehicle should be in certain areas at a certain time," O'Connell-Rodwell said.

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