Elephants are one of the loudest animals on the planet. However, oddly enough, most of the sounds they emit are not perceptible by the human ear, since they are infrasound. These ‘silent’ messages allow them tomaintain contact over distances of up to 10 kilometersand they are used to mate, guide the group or search for the young. An international team of scientists has discovered the mechanism by which elephants are capable of producing infrasound.
There are two theories to explain the emission of these low frequency sounds. The first, calledactive muscle contraction, indicates that neuronal signals cause the laryngeal muscles to contract constantly. This is the mechanism cats use to purr. The second theory is that ofmyoelastic-aerodynamic method, which occurs when air flows through the vocal cords, causing them to vibrate, something similar to what happens with human speech. In this case the neural signals are needed only to control breathing, but not to produce sound.
In short, active muscle contraction would be similar to an apparatus that needselectricityto function – in this case, brain signals – while the myoelastic-aerodynamic method would be similar to the operation of awind instrument.
How to check the method used by elephants to emit infrasound? “You can’t put an endoscope in the mouth of an African elephant and ask it to say ‘Ah’,” explains Christian Herbst, one of the authors, from the University of Vienna.
The researchers used an intact larynx from a naturally killed elephant at the Berlin Zoo andthey connected it to an air tank that served as a lung. After recording the vibrations and comparing them with infrasound emitted by elephants, the scientists concluded in their work, published in Science, that the myoelastic-aerodynamic mechanism is sufficient to produce it, without the need for neural signals. “It is the simplest explanation for the emission of infrasound by elephants,” said William Langbauer, another of the authors.
