Researchers also played recorded calls to seven captive males. The bulls reacted, too, but their response was apparently much more subtle. Perhaps the predator alarms were more traumatic to a female and potential mother. Seismic waves could travel from their toenails to the ear via bone conduction, or through somatosensory receptors in the foot similar to ones found in the trunk. We think it may be a combination of both.
Ground work The ability of large mammals to communicate long distances also is well established.
Whales, for example, produce calls that carry hundreds of miles underwater at a frequency so low that it's barely audible to the human ear. In the late 1980's, researchers discovered that elephants also produce strong, low-frequency rumbles that can travel up to 10 kilometers through the air under ideal weather conditions. I was observing them at a drinking hole when I noticed this strange set of behaviours. They would lean forward, pick up one leg and freeze for no apparent reason. She theorised that the elephants were responding to vibrations in the ground from approaching herds.