A songbirds' vocal muscles work like those of human speakers and trained opera singers, according to a new study.
The research on Bengalese finches showed that each of their vocal muscles can change its function to help produce different parameters of sounds, in a manner similar to that of a trained opera singer.
"Our research suggests that producing really complex song relies on the ability of the songbirds' brains to direct complicated changes in combinations of muscles," said lead author Samuel Sober, from Emory University in US.
"In terms of vocal control, the bird brain appears as complicated and wonderful as the human brain," said Sober said.
Pitch, for example, is important to songbird vocalisation, but there is no single muscle devoted to controlling it.
"They don't just contract one muscle to change pitch. They have to activate a lot of different muscles in concert, and these changes are different for different vocalisations," Sober said.
"Depending on what syllable the bird is singing, a particular muscle might increase pitch or decrease pitch," he said.
Previous research has showed some of the vocal mechanisms within the human "voice box," or larynx. The larynx houses the vocal cords and an array of muscles that help control pitch, amplitude and timbre.
Instead of a larynx, birds have a vocal organ called the syrinx, which holds their vocal cords deeper in their bodies.
While humans have one set of vocal cords, a songbird has two sets, enabling it to produce two different sounds simultaneously, in harmony with itself.
"Lots of studies look at brain activity and how it relates to behaviours, but muscles are what translates the brain's output into behaviour," Sober said.
"We wanted to understand the physics and biomechanics of what a songbird's muscles are doing while singing," he said.
The researchers devised a method involving electromyography (EMG) to measure how the neural activity of the birds activates the production of a particular sound through the flexing of a particular vocal muscle.
The results showed the complex redundancy of the songbird's vocal muscles.
"It tells us how complicated the neural computations are to control this really beautiful behaviour," Sober said, adding that songbirds have a network of brain regions that non-songbirds do not.
The study was published in the Journal of Neuroscience.
