Ironsides Island is home to one of the largest great blue heron rookeries in northern New York State, where over one thousand herons return to breed each April.[13] The uninhabited rocky island near Alexandria Bay, New York, is owned by The Nature Conservancy and was listed as a National Natural Landmark in 1967.[14] Calumet Island is near Clayton, New York. The privately owned island formerly featured a "castle" mansion belonging to New York tobacco tycoon Charles G. Emery, and later hosted a marina in the 1960s.[15][16] Just Room Enough Island is the smallest inhabited island in the United States.[17]