Study finds health trade-offs for wildlife as urbanization expands

by Emily Caldwell, Ohio State University

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.

Tree swallow. Photo courtesy of Ohio State University.

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.

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