Researchers have shown that humans and birds use the exact same physical mechanism to make their vocal cords move and thus produce sound, even though the two species evolved completely different organs for voice production.

"Science has known for over 60 years that this mechanism - called the myoelastic-aerodynamic theory, or in short the MEAD mechanism- drives speech and singing in humans," said Coen Elemans from the Department of Biology, University of Southern Denmark.

"We have now shown that birds use the exact same mechanism to make vocalisations. MEAD might even turn out to be a widespread mechanism in all land-dwelling vertebrates," he added.

Researchers studied six different species of bird from five avian groups. The smallest species, the zebra finch, weighs just 15 grammes, and the largest one, the ostrich, weighs 200 kilogrammes.

In the human voice box, or larynx, air from the lungs is pushed past the vocal cords, which then start moving back and forth sideways like a flag fluttering in the wind. With each oscillation the larynx closes and opens, making the airflow stop and start, which creates sound pulses.

Birds produce sound using an organ unique to them called the syrinx that is located deep in the body and therefore very difficult to study. All studied birds were shown to use the MEAD mechanism, just as humans do.

"We now managed to film sound production in birds from zebra finches to ostriches in detail using high-speed cameras. We show for the first time that birds also produce sound according to the MEAD theory," Elemans added.

The study was published in the journal Nature Communications.

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