Lean Winters

Cats, cowbirds and climate change already threaten migratory songbirds - now biologists have discovered yet another threat

• Laura Tangley
• Dec 01, 2003

As if migratory songbirds didn't have enough problems--cats, cowbirds and climate change to name just a few--biologists have discovered yet another one. In a study of American redstarts nesting near Lake Ontario, Canadian biologists analyzed blood samples (using a test that shows the kind of habitat a bird wintered in based on unique chemical signatures from plants) to look for correlations between winter habitat quality and summer breeding success. They found that redstarts that had wintered in poor scrubby habitats produced fewer chicks, and the chicks fledged later, than birds lucky enough to land a spot in a lush rain forest or mangrove swamp--a worrisome finding as these tropical ecosystems continue to vanish.