A panda in semi-wild area in Wenchuan county, Jan 27. [Photo/CFP]

In 2013, ZhangXiang, a 2-year-old female panda, was released. Last year, Hua Jiao, a 2-year-old female panda, was set free. Although nobody has seen the two since their release, researchers believe they are faring well.

But Xue Xue, released into the wild in 2014, had a tragic end.

Before her release, she had been placed in a cage for several days. One month after her release, she was found dead. Zhang Guiquan, the center's deputy chief, said it is likely she died from trauma related to being in a cage and being transported to the release site.