Traffic changing birds' songs

From ABC News:

New research has found some Australian birds are changing the way they sing so they can be heard over traffic noise.

The University of Melbourne study compared the songs of silvereyes living in cities and rural areas. It found silvereyes in urban areas sang songs and contact calls more slowly and at a higher pitch than their country relatives...

"If you're in a noisy environment and you're trying to be heard, you'd generally speak more clearly and slowly - that's what the city birds are doing as well."

[Senior research fellow Dr Kirsten Parris] says there are two possible explanations for the birds' behaviour. "The first is that it is an evolutionary shift - birds with slower, higher-pitched voices are more successful at finding mates and so are better breeders," she said. "The other is that the birds shift their own voices to suit the environment, what the researchers call plasticity."

Dr Parris says the findings show city noise may affect the birds' breeding, as the birds are being forced to use mating calls that instinctively are not as attractive to one another... "Basically the birds are presented with a trade-off between being heard at all and having the females like what they hear."

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