THE constant din of traffic is forcing nightingales in cities to sing so loudly that their songs are technically breaking legal noise levels and could be classified as a sound hazard.

The noisier the background sound, the louder male birds are forced to warble, a study in Berlin of nightingales singing next to roads, railways, parks and woodlands found. At the noisiest place, next to the Potsdamer Chaussee dual carriageway, the birds had to sing at about 93 decibels to be heard over the constant roar of the morning rush hour.

This level of sound is the equivalent of having your ear close to a motorbike exhaust at full power and means that, strictly speaking, a nightingale at full volume could be illegal.

“A nightingale next to your ear would cause severe damage to your ear for a prolonged length of time,” Henrik Brumm, a behavioural biologist at the Free University in Berlin, said. “In Germany, you are obliged to wear ear protection with more than 85 decibels for more than one hour, so working next to a nightingale means you would have to have protection.”

The loudest nightingale song was 14 decibels more than in the quieter parts of Berlin. “This does not sound much, but it corresponds to a fivefold increase in sound pressure, which means that the pressure in the bird’s lungs must be five times greater,” Dr Brumm said. “I was really quite surprised that the birds had the lung capacity to sing this loudly.”

He added: “It is unlikely that the birds suffer sore throats or laryngitis, but it may still cost them. Birds are perfectly adapted to singing, rather like opera singers, and maybe like an opera singer they get tired singing at the top of their voice.”

Songs are crucial for night-ingales, especially in late April and May when they have just arrived from their winter migration to Africa and are keen to find a mate. With a repertoire of 200 songs, the male needs every break he can get to make himself heard.

The research is published in this month’s Journal of Animal Ecology.

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