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Elephants perk up their feet for familiar sounds

The animals apparently receive vibrations through the ground, and their brains `hear' them like airborne noises.

June 02, 2007|Karen Kaplan | Times Staff Writer

The elephants' messages were urgent: Lions hunting nearby.

Instead of pricking up their ears, the other elephants listened to the warnings with their feet. But they heeded the alarms only from animals they knew, according to a new study.

For the research, scientists from Stanford University, UC San Diego and the Oakland Zoo traveled to Namibia's Etosha National Park, where they found herds of wild elephants gathered near a remote watering hole.

The researchers played a series of three 15-second warning calls recorded from elephants in Etosha or in Amboseli National Park in Kenya, according to the study, to be published this summer in the Journal of the Acoustical Society of America.

They also sent a series of meaningless tones to make sure the animals weren't just reacting to unusual vibrations.

The recordings were not transmitted through the air, but through the ground, where the sound waves could travel farther.

The 456 animals involved in the study didn't react to the meaningless sounds or the warnings from the Kenyan elephants. But when they detected the communiques from their Etosha peers, they gathered into a huddle, said Caitlin O'ConnellRodwell, a research associate in the otolaryngology department at Stanford University School of Medicine.

"If they're listening for an airborne signal, they hold their ears out -- it looks like a satellite dish," said O'Connell-Rodwell, who led the study. "When they're listening to the ground, their ears remain flat at their side. They put their weight on the front feet and sometimes lift one foot off the ground."

O'Connell-Rodwell first saw this posture 18 years ago, when she was studying plant hoppers, insects that transmit and detect sound through their feet. She said she was startled when she recognized the behavior in elephants 15 years later.

Elephants use their voices to create sounds, which propagate as waves through the ground. From the feet, the vibrations travel up the leg bone, through the shoulder and to the middle ear bones, where they are processed in the auditory cortex region of the brain just like sound waves entering through the ears, O'Connell-Rodwell said.

Elephants also use vibration-sensitive nerve cells in the feet and the trunk to carry seismic signals directly to another part of the brain called the somatosensory cortex, she said.

The new research shows that elephants can distinguish between frequencies that vary by as little as 0.75 hertz.

By comparison, humans can only tell the difference between frequencies that are at least 2 hertz apart.

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