Birdsong secrets revealed in 3D model

Front and back view of a zebra finch's syrinx The front and back view of the 3D model showing the bones surrounded by muscles

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A detailed 3D image of a bird's voice box has been created by scientists investigating how the animals sing.

Researchers in Denmark have modelled the tiny vocal organ of the zebra finch.

The study identified how the syrinx organ is adapted for rapid trills, even during flight.

According to the team, despite advances in understanding the neural control of birdsong, the physical ability is less well understood.

"Many great anatomists in the 19th Century have made absolutely wonderfully detailed drawings of the syrinx of many bird species," explained Dr Coen Elemans from the University of Southern Denmark, who led the study.

"However, now we have made a very high-resolution dataset in 3D that was not done before."

The research, published in the journal BMC Biology, focused on the zebra finch: a colourful songbird native to central Australia.

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Dr Elemans' team achieved the detailed 3D model using high-resolution imaging techniques, including magnetic resonance imaging (MRI).

The science of song

Mammals produce sounds using their larynx, an organ at the top of the windpipe, but birds have evolved a different organ.

The syrinx is found where the windpipe forks to the lungs. In zebra finches this measures just 1cm from top to bottom.

Birds rely on song to communicate essential messages about identity and reproduction but their ability to do this "on the wing" prompted Dr Elemans' analysis.

The voice box of the zebra finch The voice box of the zebra finch is located at the bottom of the windpipe

His team made three discoveries when investigating the songbirds' voiceboxes that help to explain how the finches sing so fast and maintain these complex songs in flight.

"We have shown that the bones in the syrinx are adapted for incredibly fast movement," said Dr Elemans.

"All the tiny bones are made strong but very light, so they can be moved at very high speeds. This enables a male songbird to sing very fast notes very accurately, which the females find attractive."

"We have also shown that the syrinx can be stabilised during singing [due to] a wedge-shaped bone that is connected to the sternum, the big breastplate."

In addition to bones and cartilage, the 3D model also revealed the muscle structure of the vocal organ.

"The movement of the small syrinx bones is controlled by a complicated arrangement of seven pairs of muscles. These muscles control all sorts of aspects of the produced sound, such as pitch and volume," Dr Elemans told BBC Nature.

Scientists have identified similarities between how juvenile birds mimic their parents' song and how humans learn to talk.

Start Quote

This is a crucial step to understand how the brain controls sound and turns it into those beautiful songs we are all so familiar with”

End Quote Dr Coen Elemans University of Southern Denmark

Birds have become models for many neuroscience studies in this area but the physics of avian sound production has received less attention.

"Now we have a great map to guide us and study what the function of individual muscles is," said Dr Elemans.

"Although we do not yet know which muscle contracts exactly as the bird sings, we now have a better understanding of how these 14 muscles can work together."

"This is a crucial step to understand how the brain controls sound and turns it into those beautiful songs we are all so familiar with."

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