With the twin giant panda cubs at Tokyo's Ueno Zoo turning 3 years old on Sunday, the clock is ticking for their eventual transfer to China.

The zoo in Taito Ward is currently home to the twins, Xiao Xiao and Lei Lei, as well as their father, Ri Ri, and mother, Shin Shin. The parents are on loan from China as part of a giant panda conservation agreement between the Tokyo Metropolitan Government and China's wildlife conservation society.

Under the agreement, China holds ownership of cubs born to Ri Ri and Shin Shin, so the twins will eventually be sent to the country as well.