Giant pandas may be rare, but they are aces at having twins.

Qi Zhen and Qi Yuan, twin giant pandas at the Chengdu Giant Panda Reproduction and Research Center in Chengdu, capital of southwest China's Sichuan Province, each gave birth to twin cubs on Sunday and Monday, Zhang Zhihe, director of the center, announced Tuesday.

With the birth of the four panda cubs, the number of panda cubs born in captivity this year on the Chinese mainland has risen to six, Zhang said.

The other two panda cubs were born on June 22 and Aug. 7 at the China Wolong Giant Panda Protection and Research Center, also in Sichuan.

Both pandas gave birth to their twin cubs smoothly, and the two mothers and the newborn twins are all in good health, Zhang said, adding that they had delayed announcing the births for the sake of the health of the newborn cubs.

"The chances of twins are about 50 percent for giant pandas in captivity," Yu Jianqiu, director of the Chengdu Zoo and an expert on giant pandas, told Xinhua Tuesday.

"But it's rare for wild pandas. As far as we know, there has only been one case of twins being born in the wild," Yu said.

Since the first panda cub was born in Beijing Zoo in 1963, over 60 captive pandas have given birth to twins -- more than half the total number of deliveries -- and one to triplets, according to Yu.

"There is a genetic factor, but the key factor is artificial reproduction technology," Yu explained.

"To increase the chances of pregnancy, technicians will impregnate a female with at least two male panda semen after natural mating, which makes twins and triplets pretty common for captive pandas," he elaborated.

Qi Zhen and Qi Yuan's deliveries are typical cases of natural mating combined with artificial insemination, he said.

"After natural mating, experts carry out three to five artificial inseminations," Lan Jingchao, an official with the Chengdu Giant Panda Reproduction and Research Center, told Xinhua.

The giant panda, found only in China, is one of the world's most endangered species.

Experts had previously estimated there were 1,590 giant pandas living in the wild in China, but Chinese and British scientists announced in June that there could be as many as 3,000 after a survey used a new method to profile DNA from giant panda feces.

The State Forestry Administration said there are over 180 giant pandas living in captivity on the Chinese mainland.

The Chengdu center now has 48 adult giant pandas.

Although it is common for giant pandas to give birth to twins, Yu was not optimistic about the future.

"It happens with captive pandas but it is rare with wild ones. Even if each captive panda gave birth to twins, the panda would still be an endangered species," he said.

(Xinhua News Agency August 9, 2006)