NANJING, April 18 (Xinhua) -- A league to protect red-crowned cranes on migration has been formed by five nature reserves, authorities said Wednesday.

The league includes Yancheng Wetland National Nature Reserve Rare Birds in east China's Jiangsu Province, Zhalong National Nature Reserve in northeast China's Heilongjiang Province,Xianghai Nature Reserve in northeast China's Jilin Province, Liaoning Liaohekou National Nature Reserve in northeast China's Liaoning Province, and Yellow River Delta Nature Reserve in east China's Shandong Province.

Red-crowned cranes, an endangered species, are usually found in the northeast of China, as well Japan and the Democratic People's Republic of Korea. There are about 1,000 red-crowned cranes living in the wild in total, including over 600 in China.

"Around October every year, red-crowned cranes migrate from Zhalong to Yancheng for winter and return to reproduce around March the next year, flying across natural reserves in Jilin, Liaoning, and Shandong," said Chen Hao with the Yancheng nature reserve. "The league will help ensure the safety of the birds and improve their habitat."

The reserves will build a monitoring system sharing migration information of the birds, train volunteers and strengthen patrols to protect the birds from poachers, Chen added.

Nearly 40 percent of red-crowned cranes in the wild fly to the Yancheng nature reserve every year, making it the largest wintering ground for the endangered bird. Over 3 million birds live, reproduce, winter and migrate here annually.