Patuxent Research Refuge is one of over 540 refuges in the National Wildlife Refuge System administered by the U.S. Fish and Wildlife Service. The National Wildlife Refuge System is the world’s largest network of lands and waters dedicated to protecting wildlife and their habitat. Established in 1936 by executive order of President Franklin D. Roosevelt, the Patuxent Research Refuge is the Nation's only National Wildlife Refuge established to support wildlife research. Today most of the research on the refuge is conducted by the US Geological Survey (USGS) through the Patuxent Wildlife Research Center. With land surrounding the Patuxent and Little Patuxent Rivers between Washington, D.C. and Baltimore, MD, the Refuge has grown from the original 2,670 acres to its present size of 12,841 acres and encompasses land formerly managed by the Departments of Agriculture and Defense. Throughout decades of change, Patuxent's mission of conserving and protecting the nation's wildlife and habitat through research and wildlife management techniques has remained virtually unchanged. Patuxent Research Refuge is divided into three areas: 1) North Tract, which offers hunting, fishing, wildlife observation, trails, and many interpretive programs; 2) Central Tract, where the offices and study sites of the many research biologists are located at the USGS Patuxent Wildlife Research Center; and 3) South Tract, where the National Wildlife Visitor Center and its trails are located. The National Wildlife Visitor Center and North Tract are the only areas open for visitor activities.