The sites listed here come from The American Bird Conservancy Guide to the 500 Most Important Bird Areas in the United States (2003). The boreal forest transition area encompasses the northern halves of Minnesota, Wisconsin, and Michigan, a region characterized by a mixture of coniferous and hardwood forests, nutrient-poor soils, and many clear lakes, bogs, and rivers. The forests here have the greatest diversity of nesting wood-warblers anywhere, including all of the world's Kirtland's Warblers and the majority of Golden-winged and Connecticut Warblers. Yellow Rail uses the wetland areas, as do several duck species, while large colonies of Common and Caspian Terns nest on islands in the Great Lakes. Sites #15-18 are from the region immediately to the south, the prairie hardwood transition, home to the greatest nesting waterfowl concentration outside the prairie potholes, as well as remnant Greater-Prairie Chickens and Henslow's Sparrows.
