Saturday, August 25, 2018

Listening: Feet to the Ground

Image result for african elephantEnvironmental & Science Education
Edward Hessler

Caitlin O'Connell-Rodwell has been studying the elephants at Mushara, a natural freshwater spring in Namibia's Etosha National Park for more than a quarter century. In an essay about her research KQED's Elliot Kennerson describes her work on "seismic communication among elephants, a field she pioneered back in 1997. Over the years, her work has shown that African elephants exchange information by emitting low-frequency sounds that travel dozens of miles under the ground...."

In addition to regular hearing, elephants listen for active announcements such as alarm calls and also listen passively. They "eavesdrop on each other's footsteps."O'Connell-Rodwell learned that when she "found that a predator alarm played on an above-ground speaker caused the herd to flee immediately. They responded quite differently, however, to the same call played underground. They closed ranks, but stayed put." This led her to conclude "that the elephants could tell the difference between nearby and distant dangers from how they had received the information."
All mammals have receptors for touch signals known as Pacinian corpuscles (PCs). These are hardwired "to a part of the brain...called the somatosensory cortex. In elephants, PCs are clustered around the edge of the foot." The footpad grows more than 7 cm per year but is ground down which keeps it from cracking and becoming infected, through their prodigious exercise routine. They walk about 18 hours each day on rocky and sandy soil. In the story linked below you will see a captive elephant receiving a biweekly pedicure because zoo conditions do not provide the surfaces and exercise elephants require to keep their tootsies in peak condition.
Kennerson calls attention to a distinction between hearing and feeling. In the former "airborne vibrations hit the eardrum, causing the tiny bones of the inner ear to tremble and transmit a message to the brain along the auditory nerve." When elephants sense ground vibrations "it's their sense of feeling, not hearing, at work."  These "two senses," as Dr. O'Connell-Rodwell notes, "are not quite as distinct as they seem."
Image result for african elephant
A video and Kennerson's essay are found here. The video tells how elephants use this information in regulating time at waterholes (water is a scarce resource in this dry country). Kennerson's essay includes a description of some of the subtle behaviors elephants use to announce "that new information is coming in."
I was interested to learn that Professor O'Connell-Rodwell started her career by studying planthoppers. They "communicate with each other, chiefly for reproductive purposes, by sending out vibrations over the stems of plants."
Here is a short film about life at the Mushara elephant research camp.


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