Elephants communicate primarily through sounds or vocalisations known as “rumbles”. These rumbles have fundamental frequencies in the infrasonic range below 30 Hertz, which means that they cannot be heard by humans, although the harmonics of the fundamental frequency are audible. The Stanford team has shown that these rumbles can also act as a source of Rayleigh waves that can travel through the ground.

Following on from previous work by O'Connell-Rodwell, the Stanford geophysicists studied the propagation of Rayleigh waves produced by three trained African elephants using a line of 57 geophones that began just outside the elephant enclosure and extended out to about 175 metres. They also used three microphones to measure acoustic signals in the air. Using computer models, the scientists estimated that the seismic signals produced by the elephants could travel distances up to about 2.2 kilometres through the ground, compared with only 1-2 kilometres for through the air.

“It is possible that elephants use ground waves to communicate during times when acoustic communication is not ideal, as well as over short distances to supplement acoustic communication,” Günther told PhysicsWeb.

O'Connell-Rodwell and colleagues believe that elephants sense the underground vibrations through special receptors in their feet and trunks. The team is now studying elephants at Oakland Zoo in California and in the Etosha National Park in Namibia.