Elephants are known for their ability to communicate with one another through low-frequency sounds that travel for many kilometers. But a new study published in the scientific journal Frontiers in Audiology and Otology reveals that these animals may rely on an additional mechanism that allows them to detect seismic vibrations transmitted through the ground at distances greater than 10 kilometers.
The investigation, conducted by scientists from Harvard Medical School and other international institutions, sought to understand how elephants are able to perceive very low-frequency sounds through the so-called bone-conduction hearing. This process occurs when vibrations propagate through the body and the bones of the skull to the inner ear, instead of reaching the inner ear via air through the auditory canal.
The results show that elephants have a sensitivity significantly higher than humans for this type of stimulus. According to the researchers, the explanation lies mainly in the size of their auditory anatomy: the middle-ear ossicles are about nine times heavier than those of humans, and the tympanic membranes have an area roughly seven times larger.
During the study, the scientists analyzed samples of elephants’ temporal bones and human temporal bones, subjecting them to vibrations that simulated the propagation of sound through the body. They found that the elephants’ ossicles transmitted low frequencies to the cochlea more effectively, the structure responsible for converting vibrations into neural signals interpreted by the brain.
In addition to the size of the ears, the researchers identified another possible determinant factor: the elephants’ ability to voluntarily close their ear canals through a specific muscle. This mechanism may function similarly to what happens when humans insert earplugs or earmuffs and begin to hear more intensely the sounds produced by their own body.
According to the authors, when elephants hear very low frequencies — including infrasounds between 10 and 20 hertz, used in communication between individuals — the closure of the auditory canal could significantly increase the perception of vibrations transmitted through the bones. Estimates point to an improvement that may reach up to 30-fold at certain frequencies.
The researchers believe that this discovery helps explain the effectiveness of elephants’ communication in natural environments and opens new perspectives for a better understanding of the species’ behavior. Still, they acknowledge that more studies are needed to precisely determine the elephants’ auditory sensitivity, both for sounds transmitted through the air and for vibrations propagated through the ground.
“There are few animals as majestic as elephants,” says Sunil Puria, one of the authors of the study. “Their auditory abilities could help us better understand many of their behaviors.”
