How Elephants Produce Their Deep ‘Voices’: Same Physical Mechanism Produces Vocalizations in Elephants and Humans

ScienceDaily (Aug. 2, 2012) — 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 range — fewer than 20 Hertz, or cycles, per second — that is generally below the threshold of human hearing.

African elephants are known to be great communicators that converse with extremely low-pitched vocalizations, known as infrasounds, over a distance of miles. (Credit: © catfish07 / Fotolia)


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, a senior author of the Science paper, studied it in depth.

Herbst and the other researchers imitated the elephant’s lungs by blowing controlled streams of warm, humid air through the excised larynx while adjusting the elephant vocal folds into a phonatory, or vocal-ready, position. In this way, the scientists were able to coax the vocal folds into a periodic, low-frequency vibration that matched an elephant’s infrasound in every detail.

The fact that they were able to duplicate the elephant’s infrasounds in a laboratory demonstrates that the animals rely on a myoelastic-aerodynamic, or “flow-driven,” mode of speech to communicate in the wild. The elephant’s brain would have been required to recurrently tense and relax the vocal muscles if the other mechanism, which produces a cat’s purr, was involved, they say.

This flow-induced mechanism demonstrated by the researchers is likely to be employed by a wide range of mammals. From echolocating bats with their incredibly high vocalizations to African elephants and their extremely low-pitched infrasounds, this mode of voice production seems to span four to five orders of magnitude across a wide range of body sizes and sonic frequencies.

The researchers also saw some interesting “nonlinear phenomena” in the way the elephant vocal folds vibrated. These mostly irregular patterns of vibration occur when babies cry or heavy metal singers scream and the physical mechanism that elephants use is again identical to that seen in humans, they say.

“If I scream, it’s no longer a periodic vibration,” said Herbst. “It becomes chaotic and you can hear a certain degree of roughness. This can also be observed in young elephants, in situations of high excitement.”

Herbst says that the findings were only made possible by a collaborative effort between voice scientists and biologists, and that voice science is an essential aspect of our social and economic lives.

Link:

http://www.eurekalert.org/pub_releases/2012-08/aaft-ssh080212.php

Journal Reference:

  1. C. T. Herbst, A. S. Stoeger, R. Frey, J. Lohscheller, I. R. Titze, M. Gumpenberger, W. T. Fitch. How Low Can You Go? Physical Production Mechanism of Elephant Infrasonic Vocalizations. Science, 2012; 337 (6094): 595 DOI: 10.1126/science.1219712

Citation:

American Association for the Advancement of Science (2012, August 2). How elephants produce their deep ‘voices’: Same physical mechanism produces vocalizations in elephants and humans. ScienceDaily. Retrieved August 5, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120802141527.htm

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World’s Largest Herbivore, the African Elephant, Makes Unique Food Choices

ScienceDaily (July 10, 2012) — When is an elephant a picky eater? A study of the African elephant finds that, despite its large size and fast-operating digestive system, this mammal does not eat just anything. This megaherbivore selectively chooses species and parts of the woody plants that comprise its diet.


An article in the current issue of Journal of Mammalogy explores the dietary habits of the African elephant. Researchers investigate what plants this animal selects, what parts of a plant it consumes, and how its choices vary with seasonal changes.

Previous studies suggested that the larger the animal, the less selective it might be in its diet, due to lower nutrient requirements per unit of body mass. Accordingly, a large animal would be more capable than a smaller one of digesting high-fiber content and potentially toxic chemical contents of some plants. Thus the African elephant, the largest extant herbivore, should be willing and able to consume a broad variety of plant species.

This study takes a closer look at the dietary patterns of more than 80,000 elephants in the Chobe National Park of Botswana. While its size and hindgut digestion do enable the African elephant to exploit a large assortment of plants, it seems to occupy a rather distinct niche from other animals in its actual choices.

During the wet season, elephants found only 30 percent of the woody species available for consumption palatable. In the hot, dry season, this increases to 50 percent. While the elephant might eat shoots and leaves during the wet season, it prefers stem, bark, and roots, making up 50 percent of its diet in the cool, dry season and increasing to 94 percent of it consumption in the hot, dry season.

It is not so much the choice of plant species that separates the elephant from other animals, but the selection of plant parts. The African elephant concentrates on the bark, stem, and roots rather than foliage or fruit of plants. These choices reduce the elephant’s overlap of food selection with other animals.

The food choices of the African elephant can leave a large footprint. But rather than eliminating most of the woody plant component, elephant feeding habits may cause a compositional change among the woodland species due to their neglect of certain types of plants and favor of others.

Journal Reference:

  1. Norman Owen-Smith, Jonas Chafota. Selective feeding by a megaherbivore, the African elephant (Loxodonta africana). Journal of Mammalogy, 2012; 93 (3): 698 DOI: 10.1644/11-MAMM-A-350.1