Elephants have the biggest ears in the animal world, so you'd think they would do all the listening. But watch a herd closely and you may see something odd. Every now and then the elephants freeze, lean forward, and press their weight onto their front feet, as if they're feeling for something under the ground.
That's exactly what they're doing. Elephants communicate through seismic signals, which are vibrations that travel through the earth. A stomp, a run, or a mock charge can send these vibrations a long way, and other elephants pick them up through their feet. The signals seem to travel up through the leg and shoulder bones to the middle ear. So in a real sense, elephants can "hear" through the soles of their feet.
Rumbles You Can Barely Hear
Elephants make plenty of sounds we know well, like the famous trumpet blown through the trunk. They also roar, bellow, growl, and snort. But some of their most important calls are deep rumbles so low that they're barely audible to humans. Sounds that low are called infrasound.
These rumbles are powerful. For African elephants, the calls can be as loud as 117 decibels. Because they're so low and so strong, the rumbles don't just travel through the air. They also couple with the ground and travel along the surface of the earth, which gives elephants a second channel for their messages.
Feet Built Like Listening Devices
An elephant's foot is more than a giant pillar. The cushion pads on the bottom contain nodes of cartilage, and scientists have noticed that they resemble the special acoustic fat found in toothed whales and manatees, animals that rely heavily on sound underwater.
There's another clever trick inside the ear itself. Elephants have a unique muscle around the ear canal that works a bit like a drawstring. When it tightens, it narrows the passage and dampens sounds coming through the air, which lets the animal focus more on the signals arriving through the ground.
Then there's that "freezing behaviour" researchers describe. When an elephant tunes in to ground vibrations, it leans forward and puts more weight on its larger front feet. It's the elephant version of cupping a hand to your ear.
How Far Can the Message Go?
Vibrations made by elephants on the move appear to travel up to 20 miles. Vibrations made by their rumbling calls travel about 10 miles. That's an impressive range for an animal with no phone, no radio, and no internet.
The ground is a good place to send a message. Sound in the air spreads out in every direction and fades quickly as it goes. Waves rolling along the surface of the ground lose their strength more slowly, so they hold together over longer distances. And the low frequencies elephants use, around 20 hertz, are fairly quiet in the natural world, apart from thunder or earth tremors.
Why It Matters to the Herd
These hidden messages seem to serve real purposes. When elephants detect the vibrations of an alarm call warning of predators, they take up a defensive posture and family groups pack tightly together. Researchers think long-distance signals may also help elephants find mates far away and help groups coordinate their movements across huge ranges.
Scientists also suspect that elephants may pick up natural vibrations, like those from distant thunderstorms, which could lead them toward water. That idea is still being studied, but it fits with everything else we know about how tuned in these animals are to the ground beneath them.
The study of this secret language is fairly young. In the late 1990s, researcher Caitlin O'Connell-Rodwell argued that elephants communicate over long distances with low-pitched rumbles, and Katy Payne of the Elephant Listening Project did pioneering work on elephant infrasound.
So the next time you see an elephant standing perfectly still, don't assume it's daydreaming. It may be listening to a friend several miles away, one footstep at a time.
