City noise makes robins sing at night

Urban robins living in noisy areas sing at night because they are more likely to be heard, according to research published yesterday.

Scientists in the north of England have discovered that the birds have adapted their behaviour to cope with the pressing demands of modern city life.

The study, which appears in the journal Biology Letters, disproves the myth that some robins sing at night because they believe street lighting is daylight.

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

The researchers recorded sound levels at 121 sites around Sheffield for several months in 2005 and 2006. They found robins singing during the day at 67 sites, and nocturnally at 18. At one site, where daytime traffic created a noise of 69 decibels, the scientists discovered a single robin that sang only at night.

Light level at the different sites were measured by the scientists but was shown to have less of an effect on the robins' behaviour than noise. The robins' songs, which they use to define and defend their territory as well as attract mates, are slightly higher pitched than traffic sound but the researchers added that increased urban noise levels still manage to drown out the birds' vocal efforts.

This behaviour is not without drawbacks for the bird, one of the earliest to join the dawn chorus. The birds are more likely to tire themselves out with nocturnal singing. 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."

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