The successful births of nine pairs of giant panda twins at research bases in Southwest China's Sichuan Province in the past 40 days has led to questions over whether the surge of twin births to the rare species are a result of wider use of artificial means.
Experts told the Global Times on Tuesday that the baby twins were mainly the results of natural mating, as usually about half of panda mothers give birth to twins.
On Sunday, giant panda Meiqian gave birth to twins at the Ya'an base of the China Conservation and Research Center for the Giant Panda, only one day after another giant panda, Zhuangmei, gave birth to female twins at the center's Hetaoping wild training base in Wolong.
Huang Yan, a specialist at the center, told the Global Times on Tuesday that the consecutive births of twins was not a result of artificial insemination.
"Pandas often carry twins as they usually produce two eggs when they ovulate," Huang said, adding that according to their data, around half of pandas give birth to twins.
Since June, eight pandas were born in captivity at the center's various bases, and three others - Xidou, Cuicui and Meixi - are showing signs of pregnancy, Huang said.
Pandas usually go on heat in March and April, and give birth between July and August, said Li Desheng, the center's deputy director, adding that the normal gestation period for a panda is around 120 days.
Natural mating
"The center normally lets the pandas attempt natural mating first, and if they are not successful, they try supported breeding," Li told the Global Times, adding that it is to respect the panda's right of reproduction and physiology.
Some have cast doubts over such claims.
"Maybe they simply claimed the mating was natural. In fact natural breeding is very rare among pandas," said Diao Kunpeng, a researcher at the NGO Shan Shui Conservation Center that was founded in Beijing and devoted to promoting biodiversity in western China.
Diao added that even if the pandas managed to conceive naturally, zoos and research centers will still use artificial insemination as a backup.
"It's difficult for the sperm to enter a female panda's uterus, and the pandas' eggs only survive for some 40 hours," he said.
Male pandas in captivity often don't know how to mate naturally, as they are raised in isolation and have no example to learn from, Diao said.
Most giant pandas in captivity are not good breeders. China has developed supportive breeding techniques to sustain the critically endangered species. However, only 24 percent of females in captivity give birth, posing a serious threat to the survival of the species, the Xinhua News Agency reported.
Semen struggle
Collecting and preserving panda semen is one of the greatest difficulties to artificial insemination, Li said. "But we have made breakthroughs in artificial fertilization and have well-developed techniques when it comes to rearing new-born cubs. Pandas may miscarry, or young cubs might not survive in smaller breeding bases that lack these technologies," said Li.
"Only the three bases at Wolong, Chengdu and Ya'an have mature and relatively successful artificial fertilization technologies. They have patented them and kept them secret," Diao said.
Er Shun, a giant panda on loan to Toronto Zoo in Canada from Chongqing Zoo, gave birth to twins in 2015. Yi Yanqiang, a specialist from Chongqing Zoo said that China had been providing support for artificial fertilization, breeding and rearing infants, the Chongqing Evening News reported.
Often, pandas don't make good mothers, risking the cubs' survival. In the wild, if twins are born, the mother will only rear one. Sometimes the mother kills her cub by accident.
"Normally panda mothers can only take care of one baby," said Huang. "So if they give birth to twins or even triplets, we have professional workers to take care of the others in incubators."
Pandas at the Chengdu research base gave birth to six pairs of twins in 2015, a record number, according to a Sichuan Daily report.
China has more than 1,800 giant pandas living in the wild, Xinhua reported.