The National Zoo is packing up its American-born panda cub Bao Bao for a one-way flight to China, where the 3-year-old will eventually join a panda breeding program. With Bao Bao's departure, the National Zoo will have three remaining pandas: the zoo's two adult pandas, Mei Xiang and Tian Tian, and Bao Bao's younger brother Bei Bei. Pandas born in the United States return to China, generally by age 4. With Bao Bao's departure, there will be a dozen pandas remaining in the United States: four in Atlanta, three in Washington, three in San Diego and two in Memphis, Tennessee. Four of these are on loan from China.