We're noisy, so robins sing at night

[snopes]

The puzzle of why urban robins are increasingly like to sing at night has been solved.

Scientists say the birds use song to define and defend their territories, warn of danger and to woo the opposite sex and sing at night so they do not have to compete with human noise.

It had been thought that they were confused by street lighting but today that is dismissed as an urban legend by researchers who studied robins at around 100 locations in Sheffield.

http://www.telegraph.co.uk/news/main...5/nrobin25.xml

[Richard W]

They're doing it in Ipswich too - we were listening to one outside the pub the other night. At first I assumed it was a blackbird, because blackbirds have sung at night for years, although wasn't sure because it didn't sound quite right. Then my friend spotted it and it was a robin. Then it got eaten by a sparrowhawk (not really).

Traffic noise seems a reasonable explanation for the change to me.