Human Voice and Birdsong Share Same Mechanism

Birds and humans make sounds in an identical way – this is the surprising discovery of an international scientific team whose members were also human voice experts Jan Švec and Christian Herbst from the Faculty of Science at Palacký University. The researchers have developed a unique experimental system that enabled them to examine the voice organ of birds in depth and study its functioning in detail. The findings resulting from many years of research have been published in one of the most prestigious scientific journals, Nature Communications.

The theory of sound production in humans has been known since the 1950s, when the myoelastic-aerodynamic mechanism was described by a Dutch scientist, Janwillem van den Berg. According to him, the human voice is created when air from the lungs is pushed past our flexible vocal cords, which then affect the sound based on how they are stretched by the larynx muscles. Scientists from Denmark, the United States of America and the Czech Republic have now shown that birds use the exact same mechanism to make vocalisations.

“To me it was very surprising and fascinating to discover that the sound of birds, that may resemble whistling at first, is made by the same oscillation in the birds’ vocal organs as in human vocal folds (vocal chords). It has been anticipated by some scientists, but there was no method to prove it. It has been made possible only now in Denmark by developing a very sophisticated experimental system that helped confirm the hypothesis,” said Jan Švec.

The experimental system allows the scientists to remove the vocal organ from the bird and maintain its vital functions by connecting it to an artificial blood circulation device and stimulating its nerves. A current of air is driven through it and the experts observe by means of sensors and monitors how the bird’s “vocal cords” (syrinx) function. The experts were able to scan through the avian vocal organ in order to look into its most hidden areas and capture its very rapid movements with a high-speed camera. Whereas human vocal cords are located in the larynx, the location of birds’ vocal organ varies, and so does its shape. For instance, songbirds have their syrinxes located where the trachea divides into the bronchial tubes.

“We have now managed to film the sound production mechanism in birds from zebra finches to ostriches in detail using high-speed cameras. We show for the first time that birds also produce sound in the same way as humans, that is, according to the myoelastic-aerodynamic mechanism theory,” summarises the lead author of the paper, Associate Professor Dr. Coen Elemans from the Department of Biology at the University of Southern Denmark.

Experts from the Department of Biophysics in Olomouc have been collaborating with the Danish team for about three years. According to them, the findings may be further used to study the human voice.

“The avian brain has been used as a simplified model to understand how the human brain functions in relation to vocal production and speech. The new findings about the mechanism of sound production in birds may therefore be used to improve the diagnostics of developmental and neurological disorders of voice and speech,” added Švec, whose primary specialisation in research is on the human voice. He is also known as the discoverer of videokymography – an unparalleled high-speed medical imaging method allowing the visualisation of the human vocal fold vibration dynamics and easy detection of even subtle damage to this important organ.

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