<P> The National Zoological Park, commonly known as the National Zoo, is one of the oldest zoos in the United States . It is part of the Smithsonian Institution and does not charge for admission . Founded in 1889, its mission is to "provide engaging experiences with animals and create and share knowledge to save wildlife and habitats". </P> <P> The National Zoo has two campuses . The first is a 163 - acre (66 ha) urban park located at Rock Creek Park in Northwest Washington, D.C., 20 minutes from the National Mall by MetroRail . The other campus is the 3,200 - acre (1,300 ha) Smithsonian Conservation Biology Institute (SCBI; formerly known as the Conservation and Research Center) in Front Royal, Virginia . On this land, there are 180 species of trees, 850 species of woody shrubs and herbaceous plants, 40 species of grasses, and 36 different species of bamboo . The SCBI is a non-public facility devoted to training wildlife professionals in conservation biology and to propagating rare species through natural means and assisted reproduction . The National Zoo is accredited by the Association of Zoos and Aquariums (AZA). </P> <P> The two facilities host about 1,800 animals of 300 different species . About one - fifth of them are endangered or threatened . Most species are on exhibit at the Rock Creek Park campus . The best - known residents are the giant pandas, but the zoo is also home to birds, great apes, big cats, Asian elephants, insects, amphibians, reptiles, aquatic animals, small mammals and many more . The SCBI facility houses between 30 and 40 endangered species at any given time depending on research needs and recommendations from the zoo and the conservation community . The zoo was one of the first to establish a scientific research program . Because it is a part of the Smithsonian Institution, the National Zoo receives federal appropriations for operating expenses . A new master plan for the park was introduced in 2008 to upgrade the park's exhibits and layout . </P> <P> The National Zoo is open every day of the year except for December 25 (Christmas Day). </P>

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