Male pachyderms sense female love calls within their bones

February 16th, 2009 - 2:38 pm ICT by IANS  

Washington, Feb 16 (IANS) Female elephants can transmit love calls audibly and also as low-frequency seismic vibrations that radiate up to several kilometres.

Their target, the male elephants, detect such potential mate’s signals with the help of two highly developed additional sensory systems at their disposal.

One is bone conduction, which help these vibrations travel from the toe tips into the foot bones, then up the leg and into the middle ear. The other, somatosensory reception, involves vibration-sensitive cells at the bottom of the foot that singals brain via nerves.

Caitlin O’Connell-Rodwell, ecologist and consulting assistant professor in otolaryngology at Stanford University 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.

“They are placing themselves in a way that best suits bone conduction, rather than somato-sensory reception,” she said.

O’Connell-Rodwell came to her conclusion by conducting a study of how male elephants respond to estrus calls from females. 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.

“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 travelled,” she said.

That orientation puts each of the elephant’s ears at a different distance from the sound source and 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. 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.

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, said a Stanford release.

Every time the estrus (heat) recording was played, the bulls’ behaviour 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.

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