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. The Smithsonian's National Zoo and Conservation Biology Institute cares for about 1,800 animals representing 300 species. SCBI scientists study and breed more than 20 species at their headquarters, including those that were once extinct in the wild, like black-footed ferrets and scimitar-horned oryx. Its major research initiatives are organized into six science centers: Conservation Ecology, Conservation and Sustainability, Conservation Genomics, Migratory Birds, and Species Survival. Other initiatives include the Global Tiger Initiative, Virginia Working Landscapes, and the Global Health Program. Their work doesn’t stop at the gates of SCBI. Approximately 250 SCBI scientists and students collaborate with colleagues in more than 25 countries. The Smithsonian's National Zoo and Conservation Biology Institute is one of Washington D.C.'s, and the Smithsonian's, most popular tourist destinations, with more than 2 million visitors from all over the world each year.