Elephants may be listening with their feet as well as with their ears, say researchers who are studying how well super-low frequency elephant song moves through the ground.
For about 20 years it''s been known that African elephants sing out and respond to calls so low that they are beyond human hearing. Until now, however, no one was sure if the rumbling calls were also moving through the Earth as seismic waves, possibly helping elephants communicate when there is too much noise above ground.
"They are trying to prove the concept is possible," said elephant researcher Katy Payne of the Cornell University Bioacoustics Research Program, referring to a team of Stanford University researchers who have published a paper on seismic elephant infrasound calls in the current issue of Geophysical Research Letters.
"We have several experiments going on right now to try to determine whether elephants perceive seismic cues via bone through their toenails and foot bones to their middle ear bones, or through vibration-detecting cells in the bottom of the foot," said Stanford''s Caitlin O''Connell-Rodwell, now studying the matter in Namibia.
What is clear from the Stanford team''s earlier work with trained African elephants is that under ideal conditions, elephant infrasound calls can make seismic waves that can travel almost a mile and a half (two kilometers).
The seismic signals are identical to the elephant calls in the air, says O''Connell-Rodwell.
But are the elephants really picking up distant seismic calls through their feet?
"It seems evident from their behavior," said O''Connell-Rodwell.
Telltale behaviors that an elephant is listening to a call include standing very still and adjusting their ears, explained Payne.
But since infrasound in the air is known to travel much further then a mile and a half (two kilometers), it''s hard to be sure if elephants ever notice the seismic side of their calls or use them as a back up "line" on noisy days.
To sort that out, the Stanford team is now sending elephant calls through the ground only and watching the reactions of wild elephants to see if it catches their attention.
"We are now conducting seismic playback experiments in Etosha National Park, Namibia, that will tell us for sure if they detect the signals," said O''Connell-Rodwell.
As for whether the ground can also get too noisy for seismic elephant songs, O''Connell-Rodwell says it''s possible. Generators, vehicles and airplanes all can make a lot of seismic noise and can easily drown out elephant calls entirely.