Photo taken on Jan. 9, 2016 shows red-crowned cranes at Yancheng national rare birds nature reserve, east China's Jiangsu Province. (Xinhua/Zhou Haijun)

Red-crowned cranes fly over the Yancheng national rare birds nature reserve,east China's Jiangsu Province, Jan. 9, 2016. (Xinhua/Zhou Haijun)

Photo taken on Jan. 9, 2016 shows red-crowned cranes at Yancheng national rare birds nature reserve, east China's Jiangsu Province. (Xinhua/Zhou Haijun)

Photo taken on Jan. 9, 2016 shows red-crowned cranes at Yancheng national rare birds nature reserve, east China's Jiangsu Province. (Xinhua/Zhou Haijun)

Red-crowned cranes fly over the Yancheng national rare birds nature reserve,east China's Jiangsu Province, Jan. 9, 2016. (Xinhua/Zhou Haijun)

A red-crowned cranes flies over the Yancheng national rare birds nature reserve,east China's Jiangsu Province, Jan. 9, 2016. (Xinhua/Zhou Haijun)

Photo taken on Jan. 9, 2016 shows red-crowned cranes at Yancheng national rare birds nature reserve, east China's Jiangsu Province. (Xinhua/Zhou Haijun)

Photo taken on Jan. 9, 2016 shows red-crowned cranes at Yancheng national rare birds nature reserve, east China's Jiangsu Province. (Xinhua/Zhou Haijun)