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African elephants may have magnificent ears, but on the savanna, they communicate over vast distances by picking up underground signals with their sensitive, fatty feet.
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Thousands of elephants roam Etosha National Park in Namibia, a nation in southwest Africa, taking turns at the park’s numerous watering holes. The elephants exchange information by emitting low-frequency sounds that travel dozens of miles under the ground on the savannah.
The sound waves come from the animals’ huge vocal chords, and distant elephants “hear” the signals with their highly sensitive feet. The sound waves spread out through the ground and air. By triangulating the two types of signals using both ears and feet, elephants can tune into the direction, distance and content of a message.
Seismic communication is the key to understanding the complex dynamics of elephant communities. There are seismic messages that are sent passively, such as when elephants eavesdrop on each others’ footsteps. More active announcements include alarm cries, mating calls and navigation instructions to the herd.
Seismic communication works with elephants because of the incredible sensitivity of their feet. Like all mammals, including humans, elephants have receptors called Pacinian corpuscles, or PCs, in their skin. PCs are hard-wired to a part of the brain where touch signals are processed, called the somatosensory cortex.
In elephants, PCs are clustered around the edge of the foot. When picking up a far-off signal, elephants sometimes press their feet into the ground, enlarging its surface by as much as 20 percent.
Strictly speaking, when elephants pick up ground vibrations in thei feet, it’s their sense of feeling, not hearing, at work. Typically hearing happens without physical contact, when airborne vibrations hit the eardrum, causing the tiny bones of the inner ear tremble and transmit a message to the brain along the auditory nerve.
But in elephants, some ground vibrations actually reach the hearing centers of the brain through a process called bone conduction.
By modeling how the elephant’s inner ear bones respond to seismic sound waves, scientists are hoping to use a bone-conduction approach develop new and better hearing aids for people. Instead of amplifying sound waves through the ear canal, these devices would transmit sound vibrations into a person’s jawbone or skull.
--- Where did you film this episode?
It was filmed in Etosha National Park in Namibia, at Menasha watering hole, which is closed to the public. We also filmed with the elephants at the Performing Animal Welfare Society (PAWS) sanctuary in San Andreas, Calif.
--- Do all elephants communicate seismically?
Both species of elephants – Asian and African – can pick up vibrations in their feet. There are some differences in anatomy between the two species, which cannot interbreed. Those include attributes related to their hearing, and probably arose as adaptations to their distinct habitats.
---+ Read the entire article on KQED Science:
---+ For more information:
Visit Caitlin O’Connell-Rodwell’s non-profit, Utopia Scientific. You could even go with her to Africa: http://www.utopiascientific.org/Research/mushara.html
Support the Performing Animal Welfare Society (PAWS): http://www.pawsweb.org
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