Ovenbird numbers have been in decline for decades in the Northeast and Midwest. Habitat loss is typically named as the chief culprit, although non-native earthworms were known to be a contributing factor.
Ovenbirds are a ground-nesting, forest-interior species. They rely both on large tracts of forested land and plenty of leaf-litter from which to build their beehive-oven-shaped nests. Earthworms, which are not native to the northern parts of the United States, quickly chew up fallen leaves and other forest debris, leaving the ovenbirds with few places to hide and little to build with.
Read the paper in Landscape Ecology, here. (Fee or subscription required.)
Read the Smithsonian Institution blog post on the findings, here.
The Smithsonian information has been reprinted widely around the web. A quick survey showed only verbatim copies of the blog post, but the coverage does appear to be widespread.
Photo: Ovenbird, courtesy of the Wisconsin Department of Natural Resources