Giant pandas

The giant pandas are a big hit at the San Diego Zoo. The Panda Trek houses four pandas that spend part of their day eating bamboo and playing and the other part sleeping.

(Mark Boster / Los Angeles Times)

Aug. 25, 2015 12:05 PM PT

China, which makes millions of dollars a year for its breeding programs by sending pandas to zoos around the world, controls the animals’ whereabouts.

Giant panda cub Bao Bao is given a cake to enjoy on her second birthday at Smithsonian’s National Zoological Park, in Washington, D.C., on Aug. 23, 2015. Bao Bao’s second birthday comes a day after her mother, 17-year-old Mei Xiang, gave birth to twins.

(MICHAEL REYNOLDS / EPA)

Giant panda Mei Xiang sleeps indoors at Smithsonian’s National Zoological Park in Washington, D.C., earlier this month. Mei Xiang gave birth to two panda cubs on Aug. 22, 2015.

(MICHAEL REYNOLDS / EPA)

Twin giant panda sisters Mei Huan, rear, and Mei Lun, play with their presents filled with biscuits as they celebrate their second birthday at Zoo Atlanta.

(David Goldman / Associated Press)

Xiao Liwu, a 5 1/2-month-old male panda, rolls on his back at the San Diego Zoo.

(Gregory Bull / Associated Press)

A male panda named Xiao Liwu has its head measured during its weekly checkup at the San Diego Zoo in January 2013.

(Don Bartletti / Los Angeles Times)