Great Gull Island is a 17-acre (6.9 ha) island separating the Long Island and Block Island sounds, located approximately 0.4 miles (0.6 km) southwest of Little Gull Island. Both islands are located in the town of Southold in Suffolk County, New York, and lie roughly midway between Plum Island and Fishers Island. The island is the location of former military fortifications, but is now owned by the American Museum of Natural History which is working to restore its ecosystem. It hosts many nesting Common and Roseate terns.