It turns out elephants may be listening with their feet, and their ears.

New research says elephants can communicate through ground vibrations because of their large ears and ear canals that can be sealed off at will. Scientists say that lets them stay in touch with other herd members through “vibes” over 10 kilometers away.

Elephants can already communicate across distances of up to five kilometers by producing trumpeting sounds with their trunks. But scientists said they also send signals through seismic waves traveling through the ground.

The vibrations are transmitted from elephants’ feet through their legs and through the bones of their skull directly into the inner ear. Scientists call the method “bone-conduction hearing,” and said it can be perceived across distances of 10 kilometers or more.

A new study found that bone-conduction hearing works so well in elephants because of their size and a special muscle.

Senior author Sunil Puria said: “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.

“Elephants, however, may use the ability to close their ear canals to their advantage in long distance communication.

“We found that elephants’ bone-conduction hearing is significantly improved through their larger middle ear structures and possibly further enhanced by voluntarily closing the ear canal.”

For the study, published in Frontiers in Audiology and Otology, researchers used temporal bones from deceased elephants and human donors. Temporal bones are part of the skull that houses the middle and inner ear.

The team attached the bones to a device that created vibrations mimicking sound traveling through the body into the skull. A laser beam measured how much tiny reflective markers placed on the middle ear bones moved in response to low- and high-frequency stimulation.

Researchers closed the ear canal with a soft foam plug during the experiment.

Elephant middle ear bones vibrated most effectively at a frequency of about 400 hertz, while human bones did so at around 1.2 kilohertz. Below those frequencies, elephants’ stapes, a small middle-ear bone that transmits vibrations to the inner ear, moved three to four times more than humans’ stapes.

The researchers said that does not directly mean better hearing ability, but it does mean more vibrations are transmitted to the cochlea, the part of the ear where vibrations from sound waves are translated into neural signals.

Previous studies showed elephants have better sensitivity to low-frequency hearing for air conduction, and the researchers said it stands to reason that they would also hear low-frequency bone-conducted sounds better than humans.

Study first author Caitlin O’Connell-Rodwell, of Harvard Medical School in Boston, said: “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.”

The researchers said elephants’ greater sensitivity to low-frequency sounds is likely anatomical. Their middle ear bones are nine times heavier and their eardrums seven times larger than those of humans.

In most mammals, organ size scales with body size, meaning an elephant’s middle ear is not specialized in structure compared with a human one, it is just bigger.

Puria, from the Department of Otolaryngology at Harvard Medical School, said: “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.”

Researchers also said elephants’ ability to voluntarily close their ear canals, which humans do not have, could further improve their low-frequency hearing.

They hypothesized that when listening to low frequencies of around 200 hertz or lower, elephants may contract a muscle that closes the ear canal, creating an effect similar to humans inserting earplugs or in-ear headphones.

O’Connell-Rodwell said: “Elephants produce infrasonic vocalizations in the frequency range of 10 to 20 Hz.”

Puria added: “Based on our estimates, elephants’ ability to close their ear canals could enhance their bone-conduction hearing by up to 30 times when listening to these infrasonic frequencies.

“However, the exact improvement in sensitivity would depend on the extent to which the ear canal volume is blocked by the muscle.”

The team said the study opens avenues for further research. They said the cochlea had been drained of fluids during a lengthy procurement and preparation process, which may have led to an underestimation of the results.

Elephant tissue is also scarce to obtain, which limited the number of samples.

Puria added: “There are few creatures more majestic than elephants .

“Their behavioral characteristics might be better understood through their hearing capabilities.

“We need better data about their absolute hearing sensitivity across frequencies with air and bone-conduction stimulation.

“We have tried this and found that it is easier said than done.”

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