Gravel Island National Wildlife Refuge is a small protected refuge in Lake Michigan off Wisconsin’s Door Peninsula, established in 1913 to preserve important bird breeding grounds on Spider Island and Gravel Island. The two low limestone islands, part of the Niagara Escarpment, total just 28 acres and have little vegetation because of harsh conditions and heavy nesting activity. Their significance centers on large colonies of herring gulls and double-crested cormorants, with Caspian terns breeding on Gravel Island and waterfowl using Spider Island. The refuge became the 29th in the United States, later joined the Wisconsin Islands Wilderness Area, remains closed to the public, and has long supported bird research and conservation planning.