Don: Hey Yaël, you know in old cowboy films when someone puts their ear to the      ground to listen for a stampede or wagon train in the distance?

Yaël: Yes?

D: Well, 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.

Y: But Don, ears don't help unless you can get the signal from the ground to your ear      drum! Do elephants lay their heads on the ground like cowboys?

D: Nope. 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.

Y: So I guess you might say that elephants stay alert by keeping a "foot" to the ground!  

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