Four pregnant pandas have been released into a forest in Sichuan Province so they can deliver their cubs in the wild.

The giant pandas -- Zi Zhu, Ying Ping, Cao Cao and Zhang Ka -- are now living in a 20,000 square meter tract of woodland in Hetaoping, Wolong, which was built to train pandas to live in the wild, said Tang Chunxiang, a senior expert with the Wolong China Giant Panda Protection and Research Center.

"So far, their moods are stable. Cao Cao displays the pregnancy reaction of pacing around," Tang said.

The pandas, all four or five years old, will live there until the young pandas are aged three to four, Tang said. "All of the carefully chosen pandas have experience of living in the wild and three of them, except Ying Ping, have given birth to cubs. We hope the mothers can teach their cubs life skills to help them survive in the wild."

The would-be mothers, previously kept in captivity, will produce and breed the cubs on their own, while workers at the center will observe them through surveillance cameras.

"If they need help, the workers will show up dressed in costumes that make them look like giant pandas, in order to reduce the animals' reliance on humans," Tang said.

The workers would also simulate sounds and smells of panda's natural enemies, aimed at improving their vigilance and raising their chances of survival in the wild, he said, adding that some small animals, such as squirrels and rabbits, would also be released into the woods.

This is the second phase of a plan by the research center to gradually release captive-bred pandas into the wild.

The first phase, launched in 2003, suffered a setback when Xiang Xiang, a five-year-old male, was found dead in 2007 after he was returned to the wild.

(Xinhua News Aency July 26, 2010)