Image by Daniel Foster

For millennia, humans have interacted with elephants without noticing their communications with each other. In 218 B.C., Hannibal famously led an army over the Alps with elephants in its ranks. South Asians have long harnessed them for labor. In 1883, P.T. Barnum marched them across the Brooklyn Bridge. And as Jacob Shell details in his book “Giants of the Monsoon Forest,” the Japanese Army enlisted them to help build the “Railway of Death” in World War II.

Although scientists have studied them in the wild, no one managed to observe the signals they were sending. That’s partly because while elephants communicate over vast distances by emitting low-pitched rumbles, these rumbles exist below the range of human hearing.

Nonetheless, it was still possible to glean clues about their connections through simple observation. It took Caitlin O’Connell, a postdoctoral researcher who lived among elephants, to see what no one else had: They were hearing through their feet. …

From such long and close-up cohabitation, she noticed that elephants possessed an amazing ability to, in essence, tiptoe. Once, she watched a herd, startled by a sound of approaching predators, simultaneously turn and race into the forest, while barely making a sound. They appeared to be elevated on their toes. She also noticed that elephants often stood motionless, leaning forward and digging their toenails into the ground. O’Connell wondered if they might be doing something similar to the insects she had previously studied: detecting seismic signals—sound waves transmitted through the earth. In the elephants’ case, the vibrations might be picked up via bone conduction.

O’Connell’s hunch took years of elaborate experiments to explore. Eventually … her initial hypothesis proved correct. Today, we recognize that elephants hear through their feet using bone conduction, as well as through their ears. They can hear each other’s trumpet calls from roughly two miles away, but they can detect each other’s rumbles through the earth at up to twice that distance.

If herds of elephants have always been communicating with each other over kilometers, why did it take us so long to notice? The signals were always there for us to feel. We heard their trumpet calls; we could not have missed those if we tried. But then we stopped wondering what else might connect them. We accepted what was right in front of us, and we failed to imagine anything more.