The American Physical Society (APS), in the latest podcast of ‘Life Lines’, has explained how elephant vocalizations travel through the ground for great distances, and how other elephants can understand them, just as they understand acoustic sound, which travels through the air.
Research that led to the development of the content of the podcast was done by Dr Caitlin O’Connell-Rodwell, who is the author of ‘The Elephant’s Secret Sense’.
Early in her research, Dr. O’Connell-Rodwell noticed behavior that indicates elephants are listening to acoustic (airborne) sounds by putting their ears out and orienting toward the sound’s source.
At other times, she also noticed a more puzzling behavior: Several elephants would freeze simultaneously, sometimes in mid-stride, and would press their front feet into the ground.
They might also roll a foot forward so that only their toes touched the ground. At other times, they would lift a front leg.
The behavior reminded the researcher of the behavior she saw in insects that communicate seismically.
She began a series of experiments that eventually found that:
Low-frequency elephant vocalizations, which are below the threshold of human hearing, travel through the ground in the same waveform as they do in the air.
The ground vocalization can travel faster or more slowly than acoustic sound, depending on soil conditions, but has the potential of travelling further as there is no outer limit to how far sounds can travel through the earth.