VIENNA -- The panda twins living in Vienna are to be returned to China within one month, and the training for their new journey had already started, the Vienna zoo revealed on Wednesday.

Panda twins, Fu Feng and Fu Ban, were born in August 2016. In total, their mother Yang Yang and father Long Hui gave birth to 5 cubs. But their rearing was a sensation -- for the first time a panda mother in captivity raised twins without human help.

Yang Yang was already an experienced mother after the rearing of Fu Long, Fu Hu and Fu Bao -- the three male cubs which were all back in their hometown China after two years old. In the field, panda cubs leave their mothers at this age and seek their own territory.

Fu Feng and Fu Ban are now in a training process to get used to the transport boxes. The zoo keeper regularly put in bamboo and vegetable pieces in the box, so they could sit down and feel comfortable inside. The boxes will be transported by air to China and a zookeeper will accompany the twins to China and stay there for two weeks to help them settle in their new home.

According to the contract with China, the panda cubs should be returned to China after two years old.