Seismic Communication in Elephants
How These Large Mammals Feel Vibration in Their Bodies
Feb 28, 2009
Scientists have already shown that elephants, like whales, giraffes, hippos and other animals, have the ability to communicate using subtle vocalizations that are below the human range of hearing. This is called infrasound, and it travels through the air (or in the case of whales, through water) as low-frequency waves.
But it is also known that some animals use seismic communication, which is when low-frequency waves travel through the ground. Researchers had already studied small animals and insects like blind mole rats, kangaroo rats, spiders and scorpions using seismic communication, but until recently, the theory of elephants communicating with seismic waves had not been tested.
Seismic Communication Contributes To Elephant's Social Behavior
Prior research on elephant communication focused on identifying and classifying their acoustic communication—the audible and inaudible vocalizations. Early studies in this area were spearheaded in the mid-eighties by researcher Katharine Payne, who logged more than 400 distinct elephant calls, over 60 percent of which were detected by scientific instruments but not human ears.
Ecologist Caitlin O’Connell, who wrote the 2007 book The Elephant’s Secret Sense, has spent a lot of time in the field with her husband, Tim Rodwell, and other researchers, studying elephant behavior at Etosha National Park in Namibia.
Her research showed that elephants have interesting ways of detecting sound waves traveling through the earth. They use them in coordination with other methods of communication, including acoustic, tactile, visual and chemical—all of which contribute to their social behaviors, whether for mating, warning of predators, or other purposes.
Elephant's Body Designed to Detect Low-Frequency Waves
Like whales, elephants have large middle-ear bones that are designed to detect very low frequency sounds. They can use their unique ear structure along with other body features to detect subtle vibrations. O’Connell observed elephants in a “tiptoeing posture,” or shifting their weight onto the tips of their toes or rocking back on the heel, just before a group would run off in alarm. She later concluded that fatty pads in their feet helped conduct vibrations from their toes, through the body, up to their ears. This is possible through what she calls “bone conducted hearing.”
Elephants have the ability to close off their ears to over-the-air sounds. When they close off their ears, they are more sensitive to vibrations, and therefore can “listen” to longer-range, low frequency messages traveling from the earth, up through their bodies, to their ear bones.
As an analogy for better understanding, consider how hearing-impaired people are able to “listen” to music and learn to dance by feeling vibrations in the floor. And if a person plugs their ears, their own voice can still be heard “in their head,” somewhat amplified and “felt” through vibration, too.
The tip of an elephant’s trunk is equipped with special sensory cells, too, that can be used to detect vibrations by touch. The sensory cells send messages to the brain via nerve pathways.
Elephants Create Seismic Waves in Addition to Feeling Them
O’Connell’s work showed that some elephant vocalizations, as low rumbles, traveled through the ground in addition to acoustically, but at a different speed. This meant that one signal could travel both short and long distances, increasing the elephant’s range of communication. Additionally, when elephants stampede, the vibration caused by their movement produces seismic waves that, while not generated by vocalizations, can be detected by other elephants over long distances through bone conduction.
The results of studies like O’Connell’s can be used to help understand how animals like elephants are affected by vibrations caused by natural occurrences, such as earthquakes, or by man-made activities. O’Connell’s study of seismic communication in elephants is featured online at the National Wildlife web site, in a reprint of the article “Secret Sounds of Elephants” by Mark Shwartz, published in the magazine’s April/May 2005 issue.
Other sources: Amazing Elephants, by the editors of Time-Life Books, © 1990.
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