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Elephants Make the Earth Move With Seismic “Love Calls”

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An elephant strikes a seismic sensing stance. Placing one foot on tiptoe enhances the sensitivity to seismic signals when using the bone conduction method of sensing, according to Researcher Caitlin O’Connell-Rodwell.

Photo courtesy Caitlin O’Connell-Rodwell

Elephants can communicate with one another miles apart by making subsonic calls that vibrate the ground, researchers established a few years ago.

But now a leading investigator in the field of elephant communications has discovered that elephants receiving the calls monitor the vibrating ground through both their feet and trunks. This may allow the elephants to position themselves with several points of contact on the ground to triangulate the direction of the elephant making the call.

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“Research has shown that elephants issuing calls, including those of love — more precisely, females in estrus — produce not only audible sounds, but also low-frequency seismic vibrations that can travel through the near-surface soils for distances up to several kilometers,” says a Stanford University news release about the research.

“Elephants can detect these seismic vibrations in two ways: by bone conduction, in which the vibrations travel from the toe tips into the foot bones, then up the leg and into the middle ear, and by somatosensory reception, involving vibration-sensitive cells in the bottom of the foot that send signals to the brain via nerves,” the university said.

 

Caitlin O’Connell-Rodwell discovered how elephants listen with their feet to underground vibrations by watching them in Namibia.

Photo by Max Salomon/Stanford

Caitlin O’Connell-Rodwell, an ecologist and consulting assistant professor in otolaryngology at Stanford’s School of Medicine, has been studying elephant communication for more than 15 years. During that time she’s puzzled over which seismic sensing system elephants use most often in locating the source of a call. In her most recent field season last summer, she finally got an answer, Stanford said.

“They are placing themselves in a way that best suits bone conduction, rather than somatosensory reception,” O’Connell-Rodwell said.

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She came to her conclusion by studying of how male elephants respond to estrus calls from females, Stanford said. She played recorded calls through a speaker coupled with the ground and concealed in a pile of brush near a watering hole in Etosha National Park in Namibia. The speaker emitted both an acoustic and seismic signal.

NGS Photo by Michael Nichols

“The bulls would come in and then we would test them as they headed out of the water hole in different directions. They would always place themselves perpendicular to the direction the sound had traveled,” she said.

“That orientation puts each of the elephant’s ears at a different distance from the sound source. It also creates the maximum possible difference in the distance between each of the elephant’s ears and the source. That enhances their ability to distinguish the point of origin.”

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When female elephants in estrus issue calls, they cause low-frequency seismic vibrations that male elephants, such as this one, can “listen” to with their feet and trunks, says Researcher Caitlin O’Connell-Rodwell.

Photo courtesy Caitlin O’Connell-Rodwell

This position was assumed by the elephants whether the signal was only seismic or both acoustic and seismic, suggesting that bone-conducted detection was the preferable method for detecting seismic frequencies, O’Connell-Rodwell added. “If the elephants preferred somatosensory reception, they would more likely align their front and back feet to create the greatest difference in distance from the source to each pair of feet. But perhaps that’s where the trunk comes in.”

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Every time the estrus recording was played, the bulls’ behavior was the same, O’Connell-Rodwell said. “They stop, press their trunk on the ground and position themselves and turn the other way and place their trunk on the ground and do it again,” she said.

NGS Photo by Michael Nichols

“Pressing their trunk against the ground may improve the elephant’s ability to use triangulation to locate a sound source, as using the trunk along with their (front) feet gives them the multiple (three) sensors needed for triangulating, or even front and back which would create a five-sensor array.”

O’Connell-Rodwell had observed both male and female listening behavior in previous years but hadn’t focused on the bone-conduction versus somatosensory-reception question.

Although she had noticed that both males and females often oriented themselves in a manner that seemed more conducive to employing bone conduction, until this most recent study she hadn’t tested how they responded when the sound effectively came from different locations, Stanford said.

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The scientist noticed behavioral differences in the bulls’ reactions to the estrus calls. The bulls who responded in the characteristic fashion were all either males in musth — a condition in which levels of reproductive hormones skyrocket — or subadult males, as well as juveniles too young to go into musth. But adult males who were not in musth showed very little interest in the love calls of the cows and simply walked away from the water hole, she said.

The behavior of the adult males not in musth seemed to confuse any subadult males who were with them, O’Connell-Rodwell said.

“The subadults would be torn between whether to go toward the estrus call or follow the adult male out. And they would end up following the adult out, but they kept turning back. The adult male wouldn’t pay attention at all.”

Caitlin O’Connell-Rodwell’s book describes her studies of how elephants listen to underground vibrations.

NatGeo News Watch posts about elephants:

Elephants Struggle to Cope With Poaching of Their Kin, Study Finds

Elephant Ivory Sales Stir Controversy

Elephants Imprisoned by Roads in Congo River Region

Elephants’ Legendary Memories May Be Key to Their Survival

 

 

 

Comments

  1. John McLaggan
    Houston, TX
    June 27, 11:50 am

    Possible research topic.

    In 2011 there was an earthquake in the DC area. I heard, at the time, that many animals – including the elephants – were agitated before the incident.

    Several years ago, I saw a program on TV about some elephant research in Africa. One of the points that was mentioned was that elephants communicate using sub-sonic tones. This article about Caitlin O’Connell-Rodwell’s work is similar in what it describes as far as elephants and their abilities to use sub-sonic frequencies.

    Do you suppose the elephants may have heard sub-sonic noise from the earthquake before it hit?

    Just a thought.

    John