But there was no audible sound. When I sped it up later to play back, I realized there was a communication system we didn't know about. We thought this might be a long-distance communication system. Payne, working with Joyce Poole and Catherine Moss at Amboseli National Park, have determined that elephants communicate via sound waves below the threshold of human hearing. They are thinking about, listening for and responding to one another.
Elephants also engage in audible communication when it's time to mate.
Once a year, males go through a period called musth, in which their testosterone levels rise and they begin looking for females. They issue a unique call that tells females they are in musth. Females also issue a louder call to males, usually when she has been found by one male. The female call then draws in many males from great distances. When the males arrive, they begin jousting for dominance.