End of the dawn chorus: How noise pollution is driving out birds from towns and cities

Experts say the constant rumble of cars, trucks and factories is masking the sound of the dawn chorus which males use to attract mates.

Upsetting this vital part of the breeding process could lead to a decline in the bird population.

The din also drowns out noises made by approaching predators and blocks alarm calls, leaving birds open to danger, experts say.

There is growing evidence that birds are affected by noise in urban areas. Some are singing at a higher pitch or louder, to avoid being drowned out.

Dr Richard Fuller, of Sheffield University, found some robins have abandoned the traditional dawn chorus and sing at night instead.

The change had been attributed to light pollution.

But Dr Fuller found that those parts of Sheffield with the most nocturnal singers were actually nosier in the day than other areas, New Scientist reports.

Other birds - such as nightingales - are responding to noise pollution by singing louder.

Dr Henrik Brumm at St Andrews University recorded nightingales singing between 5am and 10am.

He found that those in Berlin sang up to 14 decibels louder than those in forests.

The city birds reached volumes of up to 95 decibels - enough to send humans reaching for ear protection.

And they were loudest on weekday mornings, during rush hour. Meanwhile, great tits living in the noisiest parts of Leiden in the Netherlands, have higher pitched tunes than those in the quieter areas, according to Dr Hans Slabbekoorn, of Leiden University.

Higher melodies are more audible to other birds.

When he looked at populations of great tits in ten European cities including London, Paris and Amsterdam, he found that every one sang at a higher pitch than those in the country.

Many believe that urban noise could eventually lead to the emergence of new species. As male birds use songs to attract mates, those that can sing above the urban din - or distinguish birdsong from the background noise of cars and factories - are more likely to breed successfully.

And so, within a few generations, the genetic make up of urban birds could be subtly different from rural birds.

Some scientists believe the European blackbird has already diverged into separate urban and rural subspecies with different body shapes and life histories.

Others suspect that noise could be wiping out city birds such as house sparrows.

Their numbers have fallen by twothirds in the last few decades in Britain.

Dr Slabbekoorn said: "We don't really understand why that is, but noise may be a factor.

"House sparrows use an important low-frequency component in their calls.

"There are many factors that affect a bird's capacity for breeding in cities but noise has been the most neglected one."

Yesterday's Mail told how the number of birds visiting our gardens and parks has fallen by a fifth in four years.

The decline follows a succession of mild winters and the growing popularity of paving and decking.