for National Geographic News
Screeching brakes, wailing sirens, blaring music, roaring jetsthe constant din of city noise is enough to drive some of us to distraction. But what of the birds that must share our increasingly motorized world? Can they make themselves heard?
It's a question scientists are now trying to answer, with recent studies indicating that some birds, to avoid being drowned out completely, are making more of a racket themselves.
Nightingales in Berlin, Germany, have been found to call louder during the weekday rush hour than on weekends. Similarly, great tits living in Leiden, Netherlands, sing more shrilly in noisy neighborhoods than birds that live in quieter city precincts.
Meanwhile, a new Canadian study shows that nestlings also turn up the volume so that their parents can hear their begging above the background ruckus.
It shouldn't be a surprise that birds are so sensitive to environmental noise, says Henrik Brumm, a biologist at the University of St. Andrews, Scotland. "Few animals use acoustic communication to the same extent that birds do," he said. "That's why they are especially prone to noise interference."
Brumm, who specializes in animal communication, says such interference can potentially lead to serious difficulties for birds as they try to defend territories or attract mates.
The same pressures may apply to hungry chicks in the nest, according to a study published last week in science journal Proceedings of the Royal Society (Series B).
Canadian biologists at Dalhousie University in Halifax found that tree swallow chicks in Nova Scotia react to increased background noise, including the sound of nearby traffic, by calling louder than nestlings in quieter areas.
The researchers say it's the first study to show that ambient noise can affect bird-begging signals in this way. They add that their findings raise concerns about how chicks cope amid urban surroundings.
"Some studies suggest that begging takes a lot of energy," said the study's lead author, Marty Leonard. "If calling loudly adds to that cost, then when nestlings are forced to shout above urban noise, they might have less energy for growth. If so, they could leave the nest in poor condition."
Leonard says a chick's begging signals relay important information to its parents. "Nestling calls increase in rate and length as they get hungrier and decrease in frequency and rate as they get chilled," she said. "So calls appear to encode information on the need for food and warmth."
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