Four highly endangered red ibises have been taken back into captivity in China, after two days of free living made them lose their appetite, the official Xinhua news agency reported on Tuesday.

The birds were released into the wild at the end of May after a special training programme in a model rice paddy.

But despite being set free in an area chosen for its rich array of foods including frogs, locusts and loaches, they did not eat enough, Xinhua said.

Another 12 of the group of 26 have not been seen for five days, but the officials who organised China's first release of captive birds were not discouraged.

"They are living basically well out there," Chang Xiuyun from the Shaanxi Forestry Bureau told Xinhua.

"Crested ibises like to roam about in summer and get together to reproduce between October and November. It's too early to worry."

In past 20 years, 512 crested ibises have been artificially raised across the country, Xinhua said.