Experienced mom, 11-year-old Si Yuan. [Photo by Huang Zhiling/chinadaily.com.cn]

New mom, 10-year-old Jing Jing. [Photo by Huang Zhiling/chinadaily.com.cn]

Four male panda cubs were born to two mothers at the Chengdu Research Base of Giant Panda Breeding in Chengdu, capital of Southwest China’s Sichuan province on Sunday, bringing the number of pandas at the base to 144.

"Jing Jing, a 10-year-old, and Si Yuan, an 11-year-old, each gave birth to twins," said base chief Zhang Zhihe.

"It was the first time for Jing Jing, a mascot of the 2008 Beijing Olympics, to be a mother while Si Yuan gave birth to a cub two years ago," he said.

Jing Jing started eating less and sleeping more on July 1. On July 27 she became restless and began gnawing wood.

"At 5:40 am on Sunday, she gave birth to her first cub and more than half an hour later gave birth to her second. Both are male and weighed nearly 172 and 164 grams respectively," said Yang Kuixing, a panda expert at the base.

Si Yuan began eating less and sleeping more on July 5. On July 28, she became restless and began licking her vulva. She gave birth to her pair at 11:12 and 11:35 am. They weighed more than 174 and 180 grams.

"All four newborn cubs are healthy," Zhang said.