Pu Pu, a four-year-old panda at Shenyang Forest Zoological Garden in Liaoning, has been identified as male after having been believed to be female for four years since birth, according to the China Conservation and Research Center for the Giant Panda.

In early April, staff in the center noticed Pu Pu was showing male giant panda behavior, like walking backward and lifting his legs, and connected with the keepers at the zoo at once to confirm Pu Pu's gender.

After inspecting and checking with the center, it was determined Pu Pu was male. Experts say the gender of a giant panda is difficult to identify because the genitals of a cub, with a weight of only around 100 grams, are not clear.

In addition, many experts believed the panda's gender could only usually be recognized after the age of three. It is distinguishable by secondary sex characteristics, or the differences of the reproductive organs when exposed.