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City Bird, Country Bird

4 December 2006 (All day)
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Cities have a way of dialing up the pace of life—an environment that puts more than just humans on the fast track. Faced with the din of a booming metropolis, urban birds sing shorter and faster songs than their rural counterparts, according to a new study. These city dwellers even adjust the pitch of their voices to make sure they're heard above the ruckus.

Urbanization has traditionally been unkind to wildlife. Paving over fields and woodlands, for example, can drive local populations of birds extinct. But what about the noise a city brings? A handful of reports suggest that male birds, who sing to attract mates and defend their territories, can change the pitch of their tunes in cities. But these studies were limited to small populations in single locations.

To see how widespread the phenomenon is, ecologist Hans Slabbekoorn and colleagues at Leiden University in the Netherlands analyzed bird songs in cities and rural areas across Europe. The researchers focused on the male great tit, a common forest species that also thrives in European cities. In all, the team recorded the songs of 213 urban birds and 252 rural birds, selected from 10 large cities and their neighboring forest sites.

Just like many urbanites, city birds rush to say what needs to be said. Slabbekoorn's team found that urban great tits sang songs faster than forest tits did. City songs for both mating and territorial defense were also shorter, and higher in pitch, than forest birds' songs: A bird that sang like Barry White in the forest sounded more like Michael Jackson in the big city. The team reports its findings in tomorrow's issue of Current Biology.

The adaptation makes sense, says Slabbekoorn. Cities are full of low-frequency sounds generated by cars, trucks, and machinery such as construction equipment. By shifting their songs to higher frequencies, Slabbekoorn says, great tits "tune to a different channel," making their calls stand out from the hum of background noise.

The findings may explain why some bird species are better than others at urban survival, says Paige Warren, urban ecologist at the University of Massachusetts, Amherst. Ecologist Christopher Lepczyk of the University of Wisconsin, Madison, adds that the broad scope of the study provides the best evidence yet that urbanization can affect bird communication. "To see the same pattern emerge in locations as distant as London, Prague, and Berlin makes it harder to argue that cities don't produce these changes," he says.

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