A tree swallow perches atop a constructed nest box at Battelle Darby Creek Metro Park in central Ohio. Photos by Joseph Corra

Study finds health trade-offs for wildlife as urbanization expands

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November 23, 2020

City living appears to improve reproductive success for migratory tree swallows compared to breeding in more environmentally protected areas, a new five-year study suggests. But urban life comes with a big trade-off – health hazards linked to poorer water quality.

Researchers found that city-dwelling birds bred more nestlings because of warmer local temperatures. But they also had much higher levels of mercury in their blood – presumably from eating insects that spent their larval stages in contaminated water – than their counterparts breeding in less urban areas.

The study was conducted in central Ohio, where scientists observed tree swallows as a model species to assess their breeding success, diet and health measures in the context of varied temperatures, water quality and land use based on the location of their nests.

Despite those specifics, Ohio State University researchers consider the long-term study a harbinger of what’s to come for all sorts of wildlife as urbanization increases while the climate continues to warm, and how land-use changes are likely to harm water quality and threaten biodiversity.

Urban land accounts for about 70 million acres in the contiguous United States, representing a 470% increase since 1945.

“With urbanization expanding worldwide, we are transforming the landscape. And this isn’t going away,” said lead author Mažeika Sullivan, director of the Schiermeier Olentangy River Wetland Research Park at Ohio State. “My lab is looking at how urbanization affects multiple responses of ecosystems – what those changes are and quantifying them, but also seeing what this tells us about how we can manage and conserve ecosystems and wildlife in this context.

“Our task, knowing wildlife are using urban settings, is to think about ways to maximize benefits and minimize the risks. There’s nature in cities. So how can we make our cities a little more wild?”

Sullivan, also an associate professor in Ohio State’s School of Environment and Natural Resources, completed the work with graduate students Joseph Corra and Jeffry Hayes. The study was published online Nov. 15 in the journal Ecological Monographs.

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