Papahānaumokuākea Marine National Monument (PMNM) is the single largest conservation area under the U.S. flag and one of the largest marine conservation areas in the world. It encompasses 139,797 square miles of the Pacific Ocean (362,073 square kilometers) – an area larger than all the country's national parks combined. The extensive coral reefs found in Papahānaumokuākea – truly the rainforests of the sea – are home to over 7,000 marine species, one-quarter of which is found only in the Hawaiian Archipelago. Many of the islands and shallow-water environments are important habitats for rare species such as the threatened green turtle and the endangered Hawaiian monk seal. On less than six square miles of land, over 14 million seabirds representing 22 species breed and nest. Land areas also provide a home for four species of bird found nowhere else in the world, including the world's most endangered duck, the Laysan duck.