The San Diego Zoo is a zoo in Balboa Park, San Diego, California, housing 4000 animals of more than 650 species and subspecies on of Balboa Park leased from the City of San Diego. Its parent organization, San Diego Zoo Wildlife Alliance, is a private nonprofit conservation organization, and has one of the largest zoological membership associations in the world, with more than 250,000 member households and 130,000 child memberships, representing more than a half million people. The San Diego Zoo was a pioneer in the concept of open-air, cageless exhibits that recreate natural animal habitats. For decades, the zoo housed and successfully bred giant pandas, with the largest giant panda population outside China, before the pandas were repatriated to China in 2019. With more than 4 million visitors in 2018, San Diego Zoo is the most visited zoo in the United States. Travelers have also cited it as one of the best zoos in the world. The San Diego Zoo is an accredited member of the Association of Zoos and Aquariums (AZA), the American Alliance of Museums (AAM), and the World Association of Zoos and Aquariums (WAZA). The San Diego Zoo Wildlife Alliance also operates the San Diego Zoo Safari Park. History The San Diego Zoo grew out of exotic animal exhibitions abandoned after the 1915 Panama-California Exposition. Dr. Harry M. Wegeforth founded the Zoological Society of San Diego, meeting October 2, 1916, which initially followed precedents set by the New York Zoological Society at the Bronx Zoo. He served as president of the society until 1941. A permanent tract of land in Balboa Park was set aside in August 1921; on the advice of the city attorney, it was agreed that the city would own all the animals and the zoo would manage them. The zoo began to move in the following year. In addition to the animals from the Exposition, the zoo acquired a menagerie from the defunct Wonderland Amusement Park. Ellen Browning Scripps financed a fence around the zoo so that it could begin charging an entrance fee to offset costs. The publication ZooNooz commenced in early 1925. Animal collector Frank Buck went to work as director of the San Diego Zoo on June 13, 1923, signed to a three-year contract by Wegeforth. William T. Hornaday, director of the Bronx Zoo, had recommended Buck for the job, but Buck quickly clashed with the strong-willed Wegeforth and