Secret of the songbirds: How nightingales, skylarks, robins and other birds create their uplifting melodies

ODENSE, Denmark — Ever wonder why and how birds are whistling such beautiful songs throughout the day? The secret to the uplifting melodies of nightingales, skylarks, robins and other songbirds has finally been revealed.

Birdsong has inspired humans for centuries. Mozart, Beethoven, Vivaldi and Handel have all written music that mimic the sounds of our feathered friends. Now biologists at the University of Southern Denmark have discovered the scientific secret to the uplifting melodies of songbirds. They have super fast muscles in a unique voice box called the syrinx, through which they can control a single fiber.

The organs contract a hundred times quicker than a human’s leg muscles.

“We found songbirds have incredible fine control of their song – including below one Hertz frequency,” says study lead author Dr. Iris Adam, an assistant professor in the university’s Department of Biology, in a statement.

The study sheds fresh light on the famous dawn chorus that helps them defend territory and attract potential mates. It is based on an analysis of “motor units, or single neurons that trigger muscles. Combining tissue samples and mathematical models showed many were as small as a single fiber.

“Motor units vary in size from several hundreds or thousands of muscle fibers in our leg muscles down to only 5-10 in the muscles controlling eye position and the muscles in the larynx,” explains senior author Dr. Coen Elemans. “In zebra finch song muscles, our models predicted 13 to 17 percent of the motor neurons innervates a single muscle fiber.”

So the scientists developed a technique that measures their activity.

“Our new method allowed us for the first time to activate single motor neurons and visualize and record the activity of all responding muscle fibers simultaneously,” says Dr. Adam.”We were able to show the song muscles of zebra finches indeed contain motor units as small as one muscle fiber.”

The researchers also calculated maximum muscle stress and how it changes the frequency of the sound.

“Next to small motor units, we discovered songbird vocal muscles have the lowest stress measured in any vertebrate,” adds Dr. Adam.

Reptiles, amphibians and mammals have a larynx — a voice box at the top of the throat that protects the airways. Vocal cords vibrate to enable humans to talk, pigs to grunt and lions to roar. Birds also have larynxes. But the organ they use to make their tunes is lower down, where the windpipe splits to go into the two lungs.

The syrinx was named in 1872 after a Greek nymph who was transformed into panpipes, which have a similar structure.

“To be able to study how changes in muscle force alter the sound made by the birds’ vocal organ, the syrinx, we had to invent a new set up,” says Dr. Elemans. “This blows air through the syrinx while we can control the muscles with small motors.”

The groundbreaking findings in Current Biology reveal songbirds’ vocal muscles pack a lot of extremes.

“They are among the fastest muscles known, and now we show they are also the weakest with the highest level of control possible,” adds Dr. Adam.

This fine mastery is vital. Previous research has shown females detect these small changes. It decides if they are impressed by a male or not.

Songbirds evolved about 40 million years ago. They quickly radiated into the rich variety of 6,000 species we know today. Song is crucial for females to find and judge males. It can even drive the creation of new types.

A few important features are thought to have been important for their success. Birds need to learn their song from a tutor by imitation, just like humans.

“We think that next to a special syrinx and their amazing ability to imitate sounds, the fine graduation of the song such as pitch has increased the amount of different sounds a bird can make,” says Dr. Adam.

Birds feature in many pop and classical tunes, including Prince’s “When Doves Cry,” “Blackbird” by The Beatles, and Edward Elgar’s “Fly, Singing Bird.” Mozart is said to have bought a starling to help him write Piano Concerto No. 17. Beethoven is thought to have “plagiarized” the chirps of a warbler to finish his Second Symphony.

Birds also play important roles in Shakespeare’s plays. In Romeo and Juliet, the Lark sings at dawn and the Nightingale’s song fills the evening. At a moment of great peril, the Lark warns the lovers their time is short.

Both the Skylark and the Nightingale are nondescript birds – but their songs are unforgettable. The Danish team say they have now demonstrated why.

SWNS writer Mark Waghorn contributed to this report.