The two, born on July 15, 2013, are the first surviving panda twins ever born in the United States. Their parents, Lun Lun and Yang Yang, were sent to Zoo Atlanta in 1999 under a breeding and research agreement between China and the United States. [Photo by She Yi/ For China Daily]

The twins arrived at the base on November 5 from Atlanta zoo where they were born on July 15, 2013. They are the first surviving panda twins ever born in the United States.

Their parents, Lun Lun and Yang Yang, were sent to Atlanta in 1999 under a breeding and research agreement between China and the United States. According to the agreement, their cubs born in the United States must return to China.

Luo Yunhong, a young keeper, has taken care of Mei Lun and Mei Huan since the twin sisters arrived at the base in early November.

"They are amiable and never fight each other. Sometimes they hold each other when they sleep. They can be found eating bamboo with one's back leaning against that of the other," he said.