An elephant does not need to hear another elephant’s voice to know it is there. It can feel it. Yes, like telepathy, but not quite. You see, elephants can communicate with other elephants through sounds that can travel up to five kilometers in the air. But this is not their only way of communication. They have a second channel that runs along it: vibrations that travel through the ground travel up through the elephant’s legs, feet and skull before reaching the inner ear. A new study published in the journal in the frontier audiology and otology This explains why this system works so well for elephants.
second communication medium
Researchers at Harvard Medical School and Massachusetts Eye & Ear found that this second system, known as bone-conduction hearing, transmits signals over distances of 10 kilometers or more, about twice the range of aerial calls.“Ear canal listening devices like AirPods can be irritating because we hear body-generated sounds louder than usual, for example, when we walk or chew,” senior author Dr. Sunil Puria, associate professor of otolaryngology at Harvard Medical School and the Department of Otolaryngology at Massachusetts Eye & Ear, said in a statement.“However, elephants can 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 can potentially be further enhanced by voluntarily closing the ear canal.”
their bones keep moving
To test bone function, researchers used the temporal bones, the part of the skull that contains the middle and inner ears. They took samples from dead elephants and human donors. They mounted the bones on a device that produces vibrations that mimic sound traveling from the body to the skull. Using a laser beam, they tracked how small reflective markers moved on the bones of the middle ear. The ear canal was sealed with foam for each test.The bones of the middle ear of elephants vibrate most efficiently around 400 Hz. Human bones reached close to 1.2 kHz. Below those frequencies, the elephant stapes, a small bone that transmits vibrations to the inner ear, moves three to four times more than its human counterpart. More movement doesn’t automatically mean faster hearing; However, this means that more vibrations reach the cochlea, where it is 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 makes sense that elephants would also hear low-frequency vibrations better through bone conduction than humans.“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 first author Dr. Caitlin O’Connell-Rodwell, formerly an instructor in the Department of Otolaryngology at Harvard Medical School.
big ear
There is nothing different about an elephant’s middle ear from that of a human. It’s just bigger. This may account for elephants’ greater sensitivity to low-frequency sounds. The bones of the middle ear are nine times heavier than those of humans and the eardrums are seven times larger. So, this means that the elephant’s ear is not specialized in structure; This is even bigger.“Because of the shape of their ears, elephants can better transmit low-frequency sounds to the cochlea. “Specialization comes from the cochlea adapting to this larger input and generating neural responses that the brain can use and interpret for communication,” Puriya explained.
a muscle that acts like an earplug
Another interesting fact is that elephants can voluntarily close their ear canals. Humans do not have that ability. This may be another reason why elephants have excellent low-frequency hearing. According to the researchers, this occurs through muscle contractions, which develop when an elephant is listening to frequencies of 200 Hz or lower. This creates the effect of humans wearing earplugs or headphones.“Elephants produce infrasonic vocalizations in the frequency range of 10-20 Hz,” O’Connell-Rodwell explained.Puria said, “Based on our estimates, the ability of elephants to close their ear canals may increase their bone-conduction hearing by up to 30-fold 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 muscles.”The research also has limitations, as elephant tissue is difficult to obtain and the samples went through a lengthy preservation process. Fluid had drained from the cochlea, causing the study to underestimate the true effect.Puria concluded, “There are few creatures more majestic than elephants. Their behavioral characteristics can be better understood through their hearing abilities. We need better data about their absolute auditory sensitivity across frequencies with air and bone-conduction stimulation. We have tried this and found that this is easier said than done.”