The Sheets Island Archipelago is designated by the Audubon Society as an Important Bird Area, and many migrating bird species use these islands for breeding and nesting. Along the river, this area has the state's largest nesting population of yellow-crowned night herons, an endangered species in Pennsylvania. Wade Island is Pennsylvania's only known breeding site for the great egret and has the state's largest colony of black-crowned night herons; both are endangered species in Pennsylvania. Bald eagles and ospreys were once rare along the Susquehanna River because of pesticide use and poor environmental conditions, but after successful reintroduction efforts and improving habitat in the 1980s and 1990s, both now thrive along the river.