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Page last updated at 08:41 GMT, Wednesday, 3 June 2009 09:41 UK
'Tit townies' struggle to be heard

Great Tit
Urban great tits are less able to communicate with their country cousins

If you've ever been to an unfamiliar town and have had trouble understanding the locals, then spare a thought for the male great tit.

Researchers have found that the birds adapt to noisy urban environments, changing their song to a higher pitch in order to be heard over the city din.

Although the adaptation has been found within a few miles of the countryside, scientists at Aberystwyth University found that rural birds had trouble understanding their urban neighbours.

"Tit townies don't respond as strongly to the country boys song, nor do the country boys respond as strongly to the townies," says Dr Rupert Marshall, who led the research.

The scientists played recordings of urban and rural great tits at 20 sites around the UK.

The birds responded to the recordings by flying towards the speaker, standing by it and singing to it, just as if an intruder had entered their territory.

By timing these reactions, the researchers were able to measure the strength of the birds' response.

"They do occasionally peck the speaker, but we didn't measure that," says Dr Marshall.

Adaptation

The birds' brains are only able to adapt during the first year of their life, meaning that once the rural or urban song is learned, a mature bird cannot change its tune.

With the average bird moving by up to two miles each year, the adaptation could potentially cause problems for those birds that venture out of their neighbourhood.

A city bird moving to a new area to attract mates or find food may have difficulty warning local males to stay away.

"Were they not to be recognised at all then they would live alongside each other quite happily," explains Dr Marshall. "But as it is, it is likely they will be less successful defending their territory and finding mates."

Great tit in a bird box
The research recorded great tits in 20 locations around the UK

But all is not lost for a city bird wanting the quiet life.

Young great tits learn to sing from both their parents and the local bird population, so while an urban bird that finds itself in the country may face an uphill battle to breed, its offspring will most likely learn the rural song and so not experience the language problems of their parents.

While genetic studies have not yet been carried out, Dr Marshall believes that at the moment, the urban adaptation is most likely a case of cultural, rather than biological evolution.

"We know that a number of birds are adapting in this way but there is no evidence to suggest genetic differences between urban and rural birds," he says.

"But were song to act as a barrier to breeding, then given the island nature of most cities, surrounded by countryside, one might speculate that the gene flow may reduce between cities, leading to a reduction in genetic diversity in city populations."




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