Anna’s hummingbirds have become year-round residents thanks in part to backyard hummingbird feeders.
Steve Ringman/The Seattle Times
Anna’s hummingbirds have become year-round residents thanks in part to backyard hummingbird feeders.

Suburban development is forcing some songbirds to divorce, pack up and leave and miss their best chances for successful reproduction.

As forested areas increasingly are converted to suburbs, birds that live on the edge of our urban footprint must find new places to build their nests, breed and raise fledglings. New research published Dec. 28 in the journal PLOS ONE finds that for one group of songbirds — called “avoiders” — urban sprawl is kicking them out of their territory, forcing divorce and stunting their ability to find new mates and reproduce successfully, even after relocating.

“The hidden cost of suburban development for these birds is that we force them to do things that natural selection wouldn’t have them do otherwise,” said lead author John Marzluff, a professor of wildlife science in the University of Washington’s School of Environmental and Forest Sciences.

“Because development requires that these birds move, we force them to abandon the places they selected and go elsewhere, which often entails finding new mates when they wouldn’t have otherwise.”

Avoider birds are species that are known to decline in response to urbanization, for example when forested areas are removed for developments. In the Pacific Northwest, two avoiders are the Pacific wren and Swainson’s thrush — birds that are generally shy of humans and rely on groundcover and brush such as fallen trees, root balls, shrubs and ferns for breeding.

This work was also written about in The Seattle Times on December 28, 2016. Read “Birds in the suburbs: Faced with urbanization, some beloved species thrive, some move out“.

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