An elephant doesn’t need to hear another elephant to know it’s there. You can feel it. Yes, it’s kind of like telepathy, but not quite. As you can see, elephants can communicate with other elephants through sounds that can travel through the air over a distance of up to five kilometers.
But this is not their only way of communicating. They have a second channel running alongside it: vibrations that move through the ground itself, climbing up through the elephant’s feet, legs and skull before reaching the inner ear. A new study published in the journal border in Audiology And ear medicine Explains why this system works so well with elephants.
Second communication channel
Researchers at Harvard Medical School and Massachusetts Eye and Ear School found that this second system, known as bone conduction hearing, carries signals over 10 kilometers or more, roughly twice the range of airborne calls.“Ear canal listening devices like AirPods can be annoying because we hear sounds made by the body louder than usual, for example, when we walk or chew,” lead author Dr. Sunil Boria, an associate professor in the department of otolaryngology at Harvard Medical School and the University of Massachusetts Eye and Ear, said in a statement.“However, elephants may use the ability to close their ear canals to their advantage in communicating over long distances.
We have found that bone conduction hearing in elephants is greatly enhanced by larger middle ear structures, and is perhaps further enhanced by voluntary closure of the ear canal.
They have shaking bones
To test bone conduction, the researchers used the temporal bones, the part of the skull that includes the middle and inner ear. They took samples from deceased elephants and human donors. They attached the bones to a device that generates vibrations that mimic sound traveling through the body to the skull.
Using a laser beam, they tracked how small reflective marks on the bones of the middle ear moved. The ear canal was closed with foam for each trial.The middle ear bones of elephants vibrate efficiently at about 400 Hz. It peaked in human bones closer to 1.2 kHz. Below those frequencies, the elephant’s stapes, a small bone that transmits vibration to the inner ear, moved three to four times more than its human counterpart. More movement does not automatically mean clearer hearing; However, this means more vibrations reach the cochlea, where they are converted into signals that the brain can read.Previous research has shown that elephants have better sensitivity to low-frequency hearing through air conduction, so it stands to reason that elephants also hear low-frequency vibrations through bone conduction better than humans.“Although we doubt this based on their behavior in the wild and their responses to vibratory stimuli, it has been extremely gratifying to show that elephants have excellent bone conduction hearing,” said first author Dr. Caitlin O’Connell Rodwell, a former professor in the Department of Otolaryngology at Harvard Medical School.
The larger ear
Nothing about the elephant’s middle ear is built differently than the human ear. It’s simply bigger. This may be the reason why elephants are more sensitive to low-frequency sounds. The bones of the middle ear are nine times heavier, and the eardrum is seven times larger than human bones. This means that the elephant’s ear is not specialized in structure; It’s just bigger.“Because of the size of their ears, elephants can better transmit low-frequency sounds to the cochlea.
Boria explained that the specialization comes from the cochlea adapting to this greater input and generating neural responses that the brain can use and interpret to communicate.
A muscle that works like earplugs
Another wonderful fact is that elephants can close their ear canals voluntarily. Humans don’t have that ability. This may be another reason why elephants have excellent low-frequency hearing. According to the researchers, this happens through muscle contraction, which occurs when the elephant listens to frequencies of around 200 Hz or lower.
This creates an effect similar to that of humans inserting earplugs or headphones into the ear.“Elephants produce infrasound sounds in the frequency range of 10 to 20 Hz,” O’Connell-Rodwell explained.“Based on our estimates, the ability of elephants to close their ear canals could enhance bone conduction hearing by up to 30 times when listening to these infrasonic frequencies. However, the exact improvement in sensitivity will depend on the extent to which the volume of the ear canal is blocked by muscle,” Boria added.The research also has limitations, as elephant tissue is difficult to obtain and the samples undergo a long preservation process. The cochlea was drained of fluid, which may have caused the study to underestimate the true effect.“There are few creatures more majestic than elephants. Their behavioral characteristics can be better understood through their hearing capabilities. We need better data on their absolute sensitivity to hearing across frequencies with stimulation of air and bone conduction. We have tried this and found that it is easier said than done,” Boria concluded.