Death of the dawn chorus

Drowned out by the increasing inner-city din, robins are being forced to change their singing habits, a study reveals.

Rather than competing with the rush-hour traffic at daybreak, many are now warbling at night instead.

Richard Fuller of the University of Sheffield, who led the investigation, said: "This shows that there are subtle effects of urbanisation, and that birds are adapting their behaviour to overcome some of these problems."

Robins, usually among the first to join the dawn chorus, sing to attract mates and to ward off rivals and mark their territory.

The survey, published today in the journal Biology Letters, claims that areas with daytime noise levels that are ten decibels higher than the average rural levels are more likely to have birds that sing at night.

Despite the fact that the birds are adapting successfully to their urban environments scientists warn that changing their sleeping patterns and staying awake for longer could prove stressful.

Dr Fuller added: "If they are singing at night, it is going to take more energy than sleeping, so this may not be good news for them."

Although daybreak is commonly thought to be the trigger for birdsong, the research found that noise levels, rather than light, had a greater impact on when birds started singing.

In December last year Dutch researchers discovered that urban birds had changed the type of sound they make.

City dwelling great tits developed a high-pitched staccato song to penetrate the background noise whereas their rural counterparts relied on a lower-level twitter which was longer and slower.