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How Low Can You Go? Physical Production Mechanism of Elephant Infrasonic Vocalizations

Science  03 Aug 2012:
Vol. 337, Issue 6094, pp. 595-599
DOI: 10.1126/science.1219712

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The Song of the Elephant

In mammals, vocal sound production generally occurs in one of two ways, either through muscular control—as when a cat purrs or, more commonly, by air passing through the vocal folds—which occurs in humans and facilitates production of extremely high frequency bat calls. Over the past 20 years, it has been recognized that elephants can communicate through extremely low frequency infrasonic sounds. Taking advantage of a natural death of an elephant in a zoo, Herbst et al. (p. 595) examined the biomechanics of elephant sound production in an excised elephant larynx. Self-sustained vocal-fold vibrations, without the presence of any neural control, were used to produce infrasonic elephant sounds, using the same mechanism as singing in humans and echolocation in bats.

Abstract

Elephants can communicate using sounds below the range of human hearing (“infrasounds” below 20 hertz). It is commonly speculated that these vocalizations are produced in the larynx, either by neurally controlled muscle twitching (as in cat purring) or by flow-induced self-sustained vibrations of the vocal folds (as in human speech and song). We used direct high-speed video observations of an excised elephant larynx to demonstrate flow-induced self-sustained vocal fold vibration in the absence of any neural signals, thus excluding the need for any “purring” mechanism. The observed physical principles of voice production apply to a wide variety of mammals, extending across a remarkably large range of fundamental frequencies and body sizes, spanning more than five orders of magnitude.

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