An urban bird is changing its song repertoire to adjust to the noise of the city.
Great tits (Parus major) are singing at a higher pitch to attract a mate above the rumble of traffic.
Biologists believe it is the first known case of a wild bird changing its call sign to cope with a human-altered world.
But they warn that some species may be unable to adapt as conurbations encroach upon the countryside.
"One reason behind the success [of urban birds like the great tit] may be because they can adjust the signal that is crucial in breeding," says Hans Slabbekoorn of Leiden University in The Netherlands.
"Other species that lack such flexibility in their songs may perish or lose the opportunity to breed under noisy conditions."
The beauty of bird song has been heralded down the centuries by countless poets and playwrights.
But as the countryside is swallowed up by towns, highways and airports, some birds are having to change their age-old tunes.
The din is having a long-term effect on their behaviour, and possibly breeding habits.
ADAPTING BIRDS SING HIGH
32 male great tits in Leiden were studied
Ambient noise and bird song were recorded in various locations
Noisy territories were home to males whose songs had a higher minimum frequency
Birds in quiet areas sang more notes that reached the lowest frequencies
The study is published in the journal Nature
The Dutch study found that the great tit - which has done well in towns - appears to adjust its song to the noise around it.
Male birds in busy areas choose songs with a higher frequency to stop them being drowned out by the low frequency hum of cars, planes and machinery. Birds in quieter streets in the city dip to lower notes on the scale.
The worry is that some songbirds may be unable to survive this new selection pressure. They may stop breeding in cities and go into decline.
It could explain why birds like great tits and blackbirds have thrived in European cities while others, such as the sparrow, are disappearing.
"Great tits are fighting back in the sense that they're actually adapting to the environment around them," says Andre Farrar, spokesman for the Royal Society for the Protection of Birds in the UK.
"It's a good news story for the great tits. However, not all species can adapt to the situation we are putting them in.
"There is growing evidence that the indirect effect of traffic, such as noise and lighting, from roads is making otherwise good habitat unsuitable for a range of breeding birds."