This IBA encompasses two State Wildlife Areas with connecting habitat in between. Big Island WA covers 5,032 acres and Killdeer Plains WA 8,627 acres. The area spans part of a large former wetland prairie, historically one of the larger prairie systems found in Ohio. It is predominantly level, with areas of rolling land near the Little Sandusky and Scioto Rivers. Extensive patches of agricultural areas are found within the IBA, with more than two-thirds consisting of cropland and meadows, much of it interspersed with brushy hedgerows. The management emphasis is on grassland and wetland species through the gradual restoration of marsh and prairie habitat.Big Island is the site of the largest wetland prairie in Ohio. A 285-acre upland reservoir, as well as an annually flooded 360-acre greentree reservoir, are located at Killdeer Plains. Approximately 15% of the IBA is covered by second- and third-growth hardwood woodlots with many constructed ponds, cattail marshes, wet meadows, and planted prairies. Several thousand acres are set aside as a wildlife refuge with restricted public access. It has resident populations of Eastern massasauga rattlesnakes and Eastern plains garter snakes, as well as a huge population of various amphibians.

This IBA attracts a high diversity of both nesting and migrating species. Nesting grassland species include a variety of sparrows, Bobolinks, Eastern Meadowlarks, Northern Harriers, and Short-eared Owls. Bald Eagles nest annually. Migrants include large numbers of warblers and shorebirds, fall migrants such as Red-tailed Hawks, Rough-legged Hawks, and Northern Harriers, as well as fall populations of 50,000 migrant ducks and 11,000 migrant Canada Geese. A study run from 1990-1995 showed over twenty species of raptors used Killdeer Plains including state-listed breeders such as Bald Eagles, Northern Harriers, and Long-eared and Short-eared Owls. A breeding study by N. Moore, V. Fazio, and T. Bartlett (1995-1996) indicated that 43% of state-listed species were found as breeders and 37% used the area as migrants or winter residents.