African elephants are known to be great communicators that converse with extremely low-pitched vocalizations, known as infrasounds, over a distance of miles. These infrasounds occupy a very low frequency rangefewer than 20 Hertz, or cycles, per secondthat is generally below the threshold of human hearing.
Now, a new study shows that elephants rely on the same mechanism that produces speech in humans (and the vocalizations of many other mammals) to hit those extremely low notes. Christian Herbst from the University of Vienna, along with colleagues from Germany, Austria and the United States, used the larynx of a recently deceased elephant to recreate some elephant infrasounds in a laboratory.
Their findings are published in the 3 August issue of the journal Science, which is published by AAAS, the nonprofit science society.
"These vocalizations are called infrasounds because their fundamental frequency is below the range of human hearing," explained Herbst during a phone interview. "We only hear the harmonics of such sounds, or multiples of that fundamental frequency. If an elephant's vocal folds were to clap together at 10 Hertz, for example, we would perceive some energy in that sound at 20, 30, 40 Hertz and so on. But these higher overtones are usually weaker in amplitude."
Until now, researchers have wondered whether these low, rumbling elephant infrasounds were created by intermittent muscle contractions, as a cat's purr is, or by flow-induced vocal fold vibrations, fueled by air from the lungs, as is a human's voice. But, the natural death of an elephant at a zoo in Berlin gave Herbst and his colleagues a somewhat serendipitous chance to study the mechanism firsthand.
The researchers removed the elephant's larynx and froze it within a few hours of the animal's death. They then took it over to the larynx laboratory in the Department of Cognitive Biology at the University of Vienna, where Tecumseh Fitch
|Contact: Natasha Pinol|
American Association for the Advancement of Science