Elephants may close their ear canals at will to hear vibrations miles away

(CN) — Elephants can make plenty of noise if they choose to. When it comes to sending a message, though, it’s a more under-the-radar method they possess that has researchers intrigued.

Researchers of a study published in the ear-focused science journal Frontiers in Audiology and Otology dug into the anatomy behind bone conduction hearing — an evolutionary trait that allows elephants to communicate with each other through seismic waves, or ground vibrations, from over six miles away.

A team of scientists led by elephant expert Caitlin O’Connell-Rodwell contrasted the vibrational perception of elephants with that of humans by looking at temporal bones, where the middle and inner ear are located in both species’ skulls.

After attaching the temporal bones to a device emitting vibrations, the team measured movement in the middle ear bones, testing different frequencies. They observed greater movement within elephant middle ears at low frequencies than human middle ears, indicating that more vibrations can reach an elephant’s cochlea — a part of the ear that translates sound waves to the brain — and showing a human’s low-frequency hearing is no match for a pachyderm’s.

“Although we suspected as much based on their behavior in the wild and responses to vibrational stimuli, it was very gratifying to show that elephants have excellent bone conduction hearing,” said O’Connell-Rodwell.

Elephant middle ear bones are nine times heavier than those of humans, and elephant eardrums are seven times larger than human eardrums.

“Because of their ear size, elephants can better transmit lower-frequency sounds to the cochlea. The specialization comes from the cochlea adapting to this greater input and generating neural responses that the brain can use and interpret for communication,” said Sunil Puria of Harvard Medical School.

But size isn’t the only factor. Elephants can voluntarily close their ear canals, an effect that Puria likened to human audio accessories.

“Ear canal listening devices such as AirPods can be annoying because we hear body-generated sounds louder than normal, for example, when we walk or chew,” he said. “Elephants, however, may use the ability to close their ear canals to their advantage in long-distance communication.”

The team estimated that closing the ear canal could enhance elephant bone conduction hearing of low frequencies by up to 30 times.

What kind of signals could elephants be sending? O’Connell-Rodwell told Courthouse News that long-distance ground vibrations, caused by elephant vocalizations and stomps and perceived through their bone conduction hearing, could “improve mate-finding” and result in “better coordination” between family groups.

She added that elephants could detect vibrations from vehicles or predators, and humans could use ground vibrations as a deterrent to ward off elephants from towns and farms.

Currently working at a field site in Namibia, O’Connell-Rodwell concluded, “All in all, better bone conduction hearing would improve an elephant’s quality of life, fitness and safety.”