The researchers found striking differences in the number of young produced by flycatchers depending on how urban their nesting sites were. Non-urban sites averaged nearly two young produced each nesting season, while urban nests averaged about one young per year.
Nest survival ranged widely across sites, with 11 to 55 percent of nests successfully raising young. Nest survival, however, was not related to urbanization.
The researchers determined how urban a nest site was by measuring the percentage of land within a 1 kilometer radius that was covered by a building, parking lot, mowed lawn or other man-made surface.
As other research has suggested, this study did find that urban areas had more predators, such as raccoons, when compared to rural areas. But these predators were not raiding nests more often in urban areas, Rodewald said.
So what was reducing the number of young produced"
One problem may be that the adults birds who nested in urban areas tended to be slightly smaller although not greatly so -- than those in rural areas.
The birds are sorting out, and it appears the lower-quality birds are the ones forced into urban areas, Rodewald said. That means they have no other options there are not better rural areas for them to go.
The study showed that birds in urban areas started their nests later, already putting them at a disadvantage in the relatively short nesting season.
In rural areas, if a nest failed for some reason early in the season, the flycatchers would often make a second nesting attempt. But in urban areas, the flycatchers would often give up if their first nest in a year wasnt successful.
While many rural birds returned to the same nest site year after year, nest site turnover in urban areas was about two times higher than of those outside the city.
What is it about urban areas that Acadian Flycatchers and other migratory birds like them
|Contact: Amanda Rodewald|
Ohio State University