Mystery of elephant infrasounds revealed
3. Aug 12 1 / 4 African elephants in the Amboseli National Park, Kenia (Copyright: Department of Cognitive Biology, University of Vienna) "Science": The physics of making very low sounds
Elephants can communicate using very low frequency sounds, with pitches below the range of human hearing. These low-frequency sounds, termed "infrasounds", can travel several kilometers, and provide elephants with a "private" communication channel that plays an important role in elephants' complex social life. Their frequencies are as low as the lowest notes of a pipe organ.
Although the sounds themselves have been studied for many years, it has remained unclear exactly how elephant infrasounds are made. One possibility, favored by some scientists, is that the elephants tense and relax the muscles in their larynx (or "voice box") for each pulse of sound. This mechanism, similar to cats purring, can produce sounds as low in pitch as desired, but the sounds produced are generally not very powerful.
The other possibility is that elephant infrasounds are produced like human speech or singing, but because the elephant larynx is so large, they are extremely low in frequency. Human humming is produced by vibrations of the vocal folds (also called "vocal cords"), which are set into vibration by a stream of air from the lungs, and don't require periodic muscle activity. By this hypothesis, elephant infrasounds result simply from very long vocal folds slapping together at a low rate, and don't require any periodic tensing of the laryngeal muscles.
To find out, researchers at the University of Vienna, and the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, Germany led by voice scientist Christian Herbst and elephant communication expert Angela Stoeger, removed the larynx from an elephant (which died of natural causes), and brought it into the larynx laboratory of the Department of Cognitive Biology (headed by Tecumseh Fitch). By blowing a controlled stream of warm, humid air through the larynx (substituting for the elephants lungs), and manually placing the vocal folds into the "vocal" position, the scientists coaxed the vocal folds into periodic, low-frequency vibrations that match infrasounds in all details.
Since there can be no periodic tensing and relaxing of vocal fold muscles without a connection to the elephant’s brain, low-frequency vibrations in the excised larynx clearly demonstrate that the "purring" mechanism is unnecessary to explain infrasounds. Thus, elephants "sing" using the same physical principles as we do, but their immense larynx produces very low notes.
As an additional insight, the scientists were able to get a very clear look at some fascinating types of vibration called "nonlinear phenomena". When a baby cries, or a heavy metal singer screams, the vocal folds vibrate in an irregular manner, which is very grating to our ears. Young elephants also scream and roar, and the mechanism they use is again identical to that seen in humans.
This research shows that the physical principles underlying the human voice extend over a remarkable range, from bat's incredibly high vocalizations (too high for us to hear), all the way down to elephants’ subaudible infrasounds. How whales, the largest animals, make their even lower frequency sounds remains to be determined.
Publication in "Science":
Herbst CT, Stöger AS, Frey R, Lohscheller J, Titze IR, Gumpenberger M, Fitch WT: (2012): How low can you go? Physical production mechanism of elephant infrasonic vocalisation: Science 337, 595-599; doi: 10.1126/science.1219712
Copyright video and audio examples: University of Vienna
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- Herbst_Christian.jpg (5.9 MB)
- Stoeger_Angela.jpg (1.3 MB)
- Fitch_Tecumseh.jpg (95 KB)
- InVivo_01.wav (1.4 MB)
- exLar_01.wav (332 KB)
Contact
Dr. Roland Frey
Reproduktionsmanagement
Leibniz-Institut für Zoo- und Wilditerforschung (IZW)
Alfred-Kowalke-Str. 17
10315 Berlin, Germany
+49-30-5168 708
frey@izw-berlin.de
Dr. Christian Herbst
Department für Kognitionsbiologie
Universität Wien
1090 Wien, Althanstraße 14 (UZA I)
M +43-664-602 77-761 22
christian.herbst@univie.ac.at
Dr. Angela Stöger
Department für Kognitionsbiologie
Universität Wien
1090 Wien, Althanstraße 14 (UZA I)
M +43-676-7837326
angela.stoeger-horwath@univie.ac.at
Mag. Alexandra Frey
Pressebüro der Universität Wien
Forschung und Lehre
1010 Wien, Dr.-Karl-Lueger-Ring 1
T +43-1-4277-175 33
M +43-664-602 77-175 33
alexandra.frey@univie.ac.at