City streets have got noisier in the last thirty years – and birds have ‘raised their game’ to compensate.
A new study has shown sparrows sing louder, just as people do when talking, in order to be heard over city traffic noise.
The study has also found San Francisco streets, where the study took place, have grown noisier since the seventies, with the birds adjusting their singing to fit in with modern day commotion.
Professor David Luther from George Mason University, Washington, said birds making their homes near busy roads have to tweet louder so they can be heard, but most sparrows had stopped singing their old ditties because they were simply not loud enough to cut through the racket.
He added: ‘It’s the really low hum where almost all of this human-made noise is – in this very low bandwidth.
‘The birds can often sing at the top end of that low bandwidth and, if there’s no traffic around, that’s just fine.
‘But if they’re singing and there is noise, the lowest portion of that song gets lost, and the birds can’t hear it.’
Following on from a previous study by ornithologist Luis Baptista in 1969, the researchers found the sparrows used to sing in three distinct dialects, yet 30 years later these songs had dropped to two – with one higher-range dialect close to becoming the only song tweeted by the birds.
Professor Luther explained: ‘One dialect had basically taken over the city, officially called the San Francisco dialect.’
In the first study of its kind, researchers found territories of 20 sparrows in San Francisco’s busy Presidio district. Presidio has a lot of traffic, even more so in the morning rush hour when birds do most of their singing.
An iPod containing sparrow songs recorded from 1969 to 2005 was then set up and shuffled to see if a reaction was caused in the male white-crowned sparrows, which were the focus of the study.
Professor Luther, writing for Animal Behaviour, said: ‘The birds responded much more strongly to the current song than to the historic song.
‘The male sparrows flew toward the speaker while chirping a ‘get out of here’ song. The current songs are more of a threat.’
The researchers are going to develop this study to see how, if at all, the songs affect female sparrows.