Mental telepathy seemed as good an explanation as any for the uncanny ability of elephants to show up in the right place at the right time. How else could two groups of females, separated by large hills, find each other? Why did a young bachelor, striding confidently along an elephant path, suddenly rush off into the woods? Did he know that a rival bull was on his way? What guided a six-ton bull nearly 20 miles through the African countryside to find a female who had just come into heat?

The latest answer, almost as remarkable as thought broadcasting, is that elephants hear through their feet. The flexible, soft skin of the foot acts like a drum head, perhaps, to sense vibrations which travel from the toe nails to the ear by bone conduction. Foot stomping and low-frequency rumbling generated by one group of elephants are picked up by another group far away.

The discovery was made by Caitlin O'Connell-Rodwell, an ecologist at Stanford University, who played seismic recordings to eight elephants. Using seismic transmitters, she dispatched low-frequency rumbles like the ones elephants use in the wild to signify, "Greetings," "Warning!" and "Let's go!" Each sound had been recorded in Africa, then converted into seismic waves that the elephants could feel through the ground but not hear directly through the air. As a control, she also played them rock music.

"When the warning calls were played," O'Connell-Rodwell noted, "one female got so agitated she bent down and bit the ground. That's very unusual behavior for an elephant, but it has been observed in the wild under conditions of extreme agitation."

The female responded the same way each time the experiment was repeated. Seven males reacted too, but more subtly.

This research built upon the work of Katharine Payne, a biologist who discovered elephant rumbles when she felt throbbing in her chest while observing elephants at a zoo in 1984. She investigated the phenomenon, which she initially called "silent singing," and found that elephants communicate, in part, by producing strong, low-frequency sounds of about 20 hertz. These sounds are too low for humans to hear, but they travel through the air to alert other elephants to danger, the location of water, and mating availability.

The same infrasonic vibrations, O'Connell-Rodwell discovered in 2000, can also travel through the ground. Microphones placed 30 feet and 130 feet outside an elephant enclosure, with geophones buried in the ground beneath each microphone, picked up both "silent singing" and foot-stomping as simultaneous acoustic and seismic signals.

"Our results show that elephant rumbles travel separately through the air and the ground," O'Connell-Rodwell wrote.

Elephants crossing in front of our vehicle.
Photo by: Ann Houghton - Weir

Elephants have an urgent need to communicate over great distances; the perpetuation of the species depends on it. Because they roam freely over large areas, with no defined territory and no specific breeding season, elephants must know when and where to get together. Females live in exclusive herds, and males live alone or in bachelor herds. An elephant cow comes into estrus for only three to six days at a time, and not at all during the two years of each pregnancy and the subsequent two years she spends nursing her calf. To mate, females must be able to communicate their whereabouts to eligible males.

In addition to infrasonic sounds and stamping, elephants communicate by trumpeting through their trunks, by squealing to express juvenile distress, and by rubbing their heads against tree trunks and other markers to apply secretions that emanate from their temporal lobes. The meaning of such secretions is not well understood, at least by humans, but they tend to increase when elephants become excited or agitated.