Elephants can hear something humans can’t: conversations traveling through the ground beneath their feet.
Along with trumpets and deep rumbles that travel through the air, elephants produce low-frequency sounds that send vibrations into the Earth. Other elephants can detect these seismic signals from kilometers away.
The vibrations travel through their feet and legs before reaching the skull and inner ear, allowing elephants to effectively “hear” through their bodies.
Scientists have known about this ability for years, but exactly why it works so well has remained unclear.
Now, new research points to elephants‘ enormous middle ears and a surprising ability humans lack: they can close their ear canals to better detect vibrations traveling through their bodies.
Elephants have a hearing advantage
Study senior author Sunil Puria is an associate professor in the Department of Otolaryngology at Harvard Medical School.
“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,” said Puria.
“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.”
That’s a genuinely interesting contrast. The same body-generated noise that makes wireless earbuds annoying for humans might actually work in elephants’ favor.
Since they can shut off the usual pathway for airborne sound, elephants can tune into ground vibrations more effectively.
Putting elephant ears to the test
To understand what makes elephant hearing so effective, the researchers examined temporal bones from deceased elephants and human donors. This part of the skull houses the middle and inner ear.
They attached these bones to a device that generated vibrations mimicking how sound travels through the body into the skull.
They then used a laser to measure how much tiny reflective markers on the middle ear bones moved in response to both low- and high-frequency stimulation.
The researchers sealed the ear canal with a soft foam plug throughout the experiment.
Differences between species
The results showed a clear difference between species. Elephant middle ear bones vibrated most effectively at around 400 Hz, while human bones peaked closer to 1.2 kHz.
Below these frequencies, the stapes, a small middle ear bone responsible for transmitting vibrations to the inner ear, moved three to four times more in elephants than in humans.
Greater movement doesn’t automatically translate into better hearing.
However, it does mean more vibrations reach the cochlea, the part of the ear that converts sound vibrations into neural signals the brain can interpret.
The team reasoned that elephants’ greater sensitivity to low-frequency airborne sound would likely extend to bone-conducted sound as well.
It all comes down to size
The anatomical explanation turns out to be refreshingly simple. Elephants’ middle ear bones weigh nine times more than humans’, and their eardrums are seven times larger.
In most mammals, overall body size determines organ size, so an elephant’s middle ear isn’t structurally unique compared to a human’s. Its proportions simply reflect the elephant’s vastly larger body.
“Because of their ear size, elephants can better transmit lower-frequency sounds to the cochlea,” Puria explained.
“The specialization comes from the cochlea adapting to this greater input and generating neural responses that the brain can use and interpret for communication.”
Elephants can tune their hearing
There’s a second factor at play: elephants can voluntarily close their ear canals, something humans simply can’t do.
The researchers hypothesize that elephants may contract a specific muscle when listening for frequencies around 200 Hz or lower. This muscle closes the ear canal, creating an effect similar to humans using earplugs or in-ear headphones.
That ability could matter a great deal for how elephants communicate over long distances.
“Elephants produce infrasonic vocalizations in the frequency range of 10 to 20 Hz,” O’Connell-Rodwell said.
“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,” Puria added.
“However, the exact improvement in sensitivity would depend on the extent to which the ear canal volume is blocked by the muscle.”
More elephant secrets remain hidden
The researchers are upfront about the study’s limitations. Because procuring and preparing the tissue samples took so long, the cochleas had been drained of fluid. This may have led the team to underestimate the true results.
Elephant tissue is also notoriously difficult to obtain, which limited the number of samples available for testing.
Even with those constraints, the findings open up a genuinely promising avenue for further research into how elephants perceive and use sound.
“There are few creatures more majestic than elephants,” Puria said. “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.”
The study is published in the journal Frontiers in Audiology and Otology.
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