The US Fish & Wildlife Service manages the 586 national wildlife refuges and 37 wetland management districts that make up the National Wildlife Refuge system. That's a total of almost 96 million acres of property devoted to the protection and preservation of wildlife. Among these properties are coastal and marine areas, wetlands, prairies, and temperate, boreal and tundra forests. More than 200 species of fish, 250 species of reptiles and amphibians, 220 species of mammals and 700 species of birds call these properties home at one time or another. 75 properties also contain designated wilderness areas, to a total of more than 20 million acres. Most National Wildlife Refuges are also managed to provide some form of wildlife-dependent outdoor recreation, be it hunting, fishing, wildlife observation, bird-watching, environmental education or photography. Many refuges also contain "special management areas:" Wild and Scenic Rivers, Historic Sites, Research Natural Areas, Cultural Resource Sites, National Trails and National Natural Landmarks. Because some refuges contain habitat critical to the survival of endangered and threatened species, these refuges may be closed to public use. The National Wildlife Refuge system saw more than 75 million visits from more than 41 million visitors in 2008.