The conversion of forests to cities has hurt the populations of many kinds of birds. There are, however, a few species that appear to thrive in urban areas but little study has been devoted to the factors that affect their populations.
Researchers from the Smithsonian Migratory Bird Center monitored the nests of 5 common backyard birds:
The study area included rural, residential, and urban areas in the Washington, D.C. region. The data was collected by citizen scientists as part of the Neighborhood Nestwatch program and by scientists.
Surprisingly, the nests fared better in urban areas, sites with fewer trees and more roads, buildings, and sidewalks. This was most true in fairly large areas, about 1000 meters around the nest.
So why would urban nests do better than nests in the country or the suburbs? It likely has to do with the predator community.
To examine the predator community, fake nests were put out and monitored. They each contained 2 quail eggs and a clay-like egg that would show tooth or beak marks, depending on what tried to eat it.
The marks on the eggs showed that in urban areas, the nest predators are mostly other birds, such as jays and crows. In more rural areas, additional predators included squirrels, chipmunks, and mice. The lack of mammalian predators in urban areas seems to make nests safer.
But just because city nests are safer does not mean that urban birds have it easy. In the related articles below you can find out about the reduced amount of food in urban areas and the increased amount of contaminants.
One additional point to acknowledge is the contribution of citizen scientists monitoring nests in their own yards. Their data was compared to that of the scientists and it was found to be just as valid.
This article summarizes the information in this scientific paper:
Ryder, Thomas, Reitsma, Robert, Evans, Brian and Marra, Peter P. 2010. Quantifying avian nest survival along an urbanization gradient using citizen- and scientist-generated data. Ecological Applications, 20(2): 419-426.
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