Urban din not music to their ears

Wind-farms and motorways generate noise, annoying people who live near them. In extreme cases, it’s claimed, the din may be a threat to health and well-being. Are wild creatures also affected by noise? Recent research suggests that they are.

The Eastern bluebird, a glamorous little red and blue thrush, is the state bird of New York. Not much bigger than a sparrow, it lives in farmland orchards and parks in the US east of the Rockies. Dr Caitlin Kight, of William and Mary College Virginia, has studied the nesting performance of bluebirds in noisy and not so noisy environments. Noise, she found, can have “damaging effects on individual fitness” and is “associated with smaller brood sizes”.

Some creatures struggle to be heard over traffic sounds. Researchers at Bielefeld University in Germany recorded the ‘songs’ of 188 grasshoppers. The insects living in noisy urban areas sang louder and at a higher pitch than those in rural ones. Great tits in European cities sing more vigorously the noisier the environment. Robins, famously, have taken to performing at night. The presence of artificial light, it’s said, is responsible for this. It’s also possible, that they are avoiding the cacophony of the daylight hours. Singing is important; a territory-holding male needs to get his message out if he’s to attract a mate and prevent rivals from taking over his territory. If he can’t be heard, he’s in trouble.

‘Unnatural’ selection could account for such changes in behaviour. Birds with an innate tendency to sing loudly would be better able to secure mates and defend territories in noisy environments. Succeeding at the expense of less vigorous singers, they would father more offspring and, over several generations, loud singing would become the norm.

There could, however, be another explanation. Researchers at the Max Planck Institute found nightingales in Berlin sang more vigorously on weekdays when there was heavy traffic than at weekends when things were quieter. This suggests birds can monitor noise levels and adjust the volume of their songs in response to them.

Dr Kight agrees. She and her colleagues recorded the songs of 32 bluebird males occupying nest-boxes and compared the sound levels of each individual when his environment was noisy and when things were quiet. The birds altered the strength of their singing depending on the background noise. Songs also became lower-pitched as noise levels increased; low frequency sounds travel better than high frequency ones. Bluebirds, it seems, behave like people at noisy parties; they shout louder to make themselves heard. This study shows conclusively that birds can adjust their singing in real-time to take account of noise. The birds seem to ‘know’ that it’s not enough just to sing; that it’s the message which counts.

Dealing with changes in environmental noise, Kight thinks, may be nothing new for wild creatures. The sound of waterfalls can increase dramatically when rivers are in flood. Woods are noisy places during storms. Rush-hour traffic, from a bird’s point of view, is not so different.

We shouldn’t conclude from this, she and her colleagues warn, that birds cope well with noise and that it has few implications for health and well-being. Environments can become so noisy that, no matter how loudly they sing, birds are unable to communicate effectively with each other and fail to breed successfully. This study focused on song, which is used during the breeding season, but birds rely on sounds for a variety of purposes throughout the year. Nestlings call on their parents to feed them and fledged birds communicate vocally with adults and each other. Man-made noise, disrupting these communications, may have adverse effects. Should potential noise pollution at nearby nature reserves be taken into account when locating noisy factories, roads or airports?

C Kight et al, Eastern bluebirds alter their song in response to anthropogenic changes in the acoustic environment, Integrative and Comparative Biology, 2015.


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