Image caption The project's "holy grail" was replicating the complex song of the zebra finch

A simple rubber device that replicates complex bird songs has been developed by a team of US researchers.

The song is produced by blowing air through the device, which mimics a bird's vocal tract, the team explained.

The findings appear to challenge the idea that birds had to learn complicated neurological controls in order to produce distinctive calls.

The team plans to share its data with biologists to see if it sheds new light on how birds produce complex songs.

"I definitely did not think that I would be able to produce a whole bird song when we started," explained Aryesh Mukherjee, a member of the project team from Harvard University, which was led by Professor L Mahadevan.

"We were just playing around and I probed the device in a certain way and it started playing a bird song - that was very exciting."

He added that the design of the device was very rudimentary: "It is made out of two pieces of rubber, which are stuck together but leaving a little area in the middle that forms the 'vocal tract'."

As well as the air source, the device is pressed together by a motor that replicates the action of a contracting muscle.

"In the terms of physics, the tract is just an elastic membrane of springs. If you tense it correctly, and probe it in a certain way, it starts vibrating," Mr Mukherjee told BBC News.

"Our project was to control the frequency of those vibrations."

The team were able to replicate a number of bird-songs, such as Bengalese finches and vireos, and were able to closely model the song of zebra finches.

"Making it sound like a zebra finch is the holy grail of the project," Mr Mukherjee said.

"We have been able to come pretty close to it, but we have been able to replicate other bird species much better."

He suggested that the song of the zebra finch was a little bit more complex, therefore it required a little fine tuning.

"But we are getting close," he added.

Good vibrations

The team's discovery was made during a project to learn more about the physical behaviour of vocal tracts.

Image caption The surprisingly simple design was able to replicate complex birdsong of a range of species

"We were working with neuroscientists who were trying to understand how a bird learns to sing.

"It was considered a very complicated process, and we tried to uncover some of the mysteries with physics."

Bird-song, a complex sound full of intricate patterns and rich harmonies, has been the subject of many studies. Neuroscientists, over the years, have provided insights into how young birds learn their songs from adult birds, requiring a series of complex neurological changes in order for them to control their voices.

But Mr Mukherjee said the project's results showed that it was possible to replicate bird-song without high degrees of control inputs.

"By just having one muscle (motor pressing the device) in the equation, you can get a lot of sounds," he explained.

"Translating that back into the idea of neurological control... it suggests that the control needed to produce seemingly complex songs is not as challenging as previously thought."

However, Mr Mukherjee said that whether this challenges current thinking on how birds produce their song was outside their area of expertise.

"We are in no position to make a claim about what this has to do with bio-physics or neurological control within birds. All we can say is what we have learned from our experiments, and share that information with biologists.

Another member of the team Shreyas Madre - now an assistant professor at Brown University, Rhode Island - is developing a mathematical model to see if it is possible to identify some of the key principles in producing complex birdsong.

The team plans to publish its findings in a paper in the near future.