You've probably seen cowboys in Westerns sometimes puts their ear to the ground to listen for a stampede or wagon train in the distance. But did you know that elephants can also communicate with seismic signals–sounds transmitted through the ground–sort of like in those old cowboy films? The difference is that elephants not only listen to, but produce loud low-pitched sounds that travel long distances through the ground.
Elephants have evolved some special adaptations that may help with detecting the subsonic seismic signals. For starters, their ears are tuned to hear lower sounds than other land mammals' ears.
Unlike cowboys, the elephants don't need to put their ears against the ground to hear the sounds well. Playback studies show that elephants can hear and discriminate different kinds of seismic calls standing up. For example, when scientists played alarm calls with special underground "rumble speakers," nearby elephants froze and then moved into defensive postures.
Scientists think elephants may pick up the sounds using their feet like microphones that transmit the signal to their ears by bone conduction. Vibrations from the ground travel through the feet up through bones in the legs, shoulders, and skull to the ear. Elephant feet actually contain a dense pad of fatty tissue that is thought to help amplify the sound. In addition, the skin on the bottom of their feet contains special touch-sensitive cells called Pacinian corpuscles. These sensory cells may also help with detection or discrimination of sound vibrations in the ground. You might say that elephants stay alert by keeping a "foot" to the ground!