Twin pandas Meilun (L) and Meihuan play at the Chengdu Research Base of Giant Panda Breeding in Chengdu, southwest China's Sichuan Province, Dec. 6, 2016. Meilun and Meihuan, the twin giant pandas that were born in the United States, traveled back to Chengdu on Nov. 6, 2016 and have been quarantined for one month following the rules of China's animal and plant quarantine law. The twins were born in July, 2013 in Atlanta, U.S.. Their parents, Lunlun and Yangyang, have been living in the United States since 1999. According to the lease agreement between China and U.S., pandas that are born abroad should be returned to China by the age of four. (Xinhua/Xue Yubin)

CHENGDU, Dec. 6 (Xinhua) -- The first pair of surviving giant panda twins ever born in the United States are adapting well to their new life in southwest China's Sichuan Province, breeders have said.

The sisters, Mei Lun and Mei Huan, have just finished a month-long quarantine check at the Chengdu Research Base of Giant Panda Breeding, after they flew back from Zoo Atlanta in the United States early November, with both in good health, said Chen Xin at the base's disease prevention and control department.

They are gradually changing their diet from biscuits, which they received in the United States, to bamboo, apple and Chinese steamed bread, according to their keeper Luo Yunhong.

The sisters are on good terms, said Luo.

"They've never fight. Sometimes they hug each other when sleeping, and eat bamboo, back to back."

Born on July 15, 2013, the twins received their names, meaning "something indescribably beautiful, and magnificent," via an online vote.

They are the fourth and fifth offspring of Lun Lun and Yang Yang, who came to Zoo Atlanta in 1999 under a collaboration agreement between China and the United States.

As part of the agreement, panda cubs born in the United States to parents on loan from China must be returned to China.

Lun Lun has given birth to seven cubs over five pregnancies.