Thursday, July 12, 2012
Noise Pollution Evolution: City Bird and Country Bird
The study was performed by the University of Sheffield's Julie Schroeder, who found that loud noises drown out communication between mother house sparrows and their chicks, including the calls chicks make to beg for food. Only a handful of other studies have examined the effect of loud noises on songbirds mating and nesting habits, though none have quite tackled the serious maternal questions raised long ago in Dr. Seuss's seminal work, Are You My Mother? Sheffield's study is also made unique by the fact that she focused on a well-known group of sparrows living on Lundy Island, in Devon, England. These sparrows regularly trade swap their eggs among nests, which results in some parents raising chicks they're not related to (and I find myself wondering if all sparrows do this, or if it's just a British thing). This kid-swapping helped researchers separate the effect of a sparrow's parentage from the effect of its environment, just in case the genetically weaker sparrows were somehow more prone to doing something stupid... like live next to a roiling electrical generator, which is exactly what some of them were doing.
The generators on Lundy Island (built in 2001) run continuously from 6 to 9 pm and emit 70 decibels of noise. Schroeder compared the nest boxes located in the generators' noise zone to nests located in a quieter zone. She found that, while the noise has no real effect on the health of adult birds (female birds could even lay the same number of eggs), it did adversely affect their offspring. Though chicks in quiet areas had a 25 percent chance of living long enough to fledge (such are the harsh realities of birdy life), the chicks in noisy areas had only a 21 percent chance. Plus, those urban chicks weighed less than their country counterparts, most likely, Schroeder believes, because mother birds visited their chicks less often and provided them with less food.
The fact that adult birds seemed in fine health led Schroeder to single out noise as the culprit in the weakness of urban chicks, since, say, if air pollution had been stunting chick growth, adults would have been unhealthy too. Researchers suspect these findings may help explain the house sparrow's sudden disappearance in Western Europe and North America. "If what we suggest takes place in big cities too," she says, "it is likely to play an important role in the sparrow population dynamic, and is probably one cause of the dramatic population crash that we are currently observing." Discovery Magazine reminds us that the exact cause of the chicks' undernourishment is still uncertain — there may very well be a barrier between mother and chick communication in urban areas or loud noises may scare off insects the birds eat.
It's probably pretty important, though, for us to keep track of the plight of these songbirds, lest -God forbid!- the pigeon become the only bird we can look forward to seeing on our stroll to work in the big city