Panda researchers at Wolong base in southwest China's Sichuan Province are planning to release six more pregnant bears into a semi-wild environment this year hoping to help more captive-bred pandas return to the wilderness.

The move is aimed at expanding a wild training program that has proven successful with panda mother Cao Cao and her cub, Tao Tao, the first-ever baby panda born under wild training, said Huang Yan, a senior zoologist and head of Wolong's wild training base.

"The two pandas are very healthy and have acquired basic survival skills in the wild," he said at a meeting with panda experts at the Wolong Nature Reserve Administration Thursday.

Tao Tao survived a blizzard in March and has become more independent. "He's learned to mark and guard his own territory, a trait only wild pandas have."

Cao Cao was released into a semi-wild environment at Wolong Nature Reserve during her pregnancy in July 2010. A month later, she gave birth to Tao Tao, a male cub.

In February, the mother and cub were transferred into a much larger training base in Wolong. Though still fenced, their new home, rich in vegetation, is almost the same as the wilderness.

The pandas will live there until the young panda turns two and a half years old, in early 2013, said Huang.

At that time, Tao Tao will be released into the wild mountains.

Panda keepers will stop feeding the two pandas by the end of this year and leave them to search for their own food, Huang said.

Over the past year, zoologists had kept an eye on the pandas and continued to provide them with food when necessary. To simulate a wild environment as much as possible, zoo workers and vets who entered the zone always disguised themselves as pandas by donning a black-and-white fur coats and crawling on the ground.

In the next phase of the wild training, however, workers would use the sounds and smells of panda's natural enemies, such as leopards, to enhance the bears' vigilance and raise their survival chances in the wild.

"We might also disguise ourselves as leopards and scare the pandas to warn them of potential danger in the wild," said Huang.

China's plan to save the endangered species by releasing captive-bred pandas back into the wild began in 2003, with Xiang Xiang, a male cub being trained to survive in the wild.

Xiang Xiang was released into the wild in 2006, but was found dead 10 months later in a remote corner of Wolong. He had apparently been attacked by wild pandas native to the place.

The program was resumed last year at two panda research centers, in Wolong and Chengdu.

Most giant pandas in captivity are not good breeders. Only 24 percent of females in captivity give birth, posing a serious threat to repopulation.