Migratory birds are seen at a wetland on Balikun grassland in northwest China's Xinjiang Uygur Autonomous Region in September. (Photo: China News Service/ Zhang Jiangang)

Migratory birds are seen at a wetland on Balikun grassland in northwest China's Xinjiang Uygur Autonomous Region in September. (Photo: China News Service/ Zhang Jiangang)

Migratory birds are seen at a wetland on Balikun grassland in northwest China's Xinjiang Uygur Autonomous Region in September. (Photo: China News Service/ Zhang Jiangang)

Migratory birds are seen at a wetland on Balikun grassland in northwest China's Xinjiang Uygur Autonomous Region in September. (Photo: China News Service/ Zhang Jiangang)

Migratory birds are seen at a wetland on Balikun grassland in northwest China's Xinjiang Uygur Autonomous Region in September. (Photo: China News Service/ Zhang Jiangang)

Migratory birds are seen at a wetland on Balikun grassland in northwest China's Xinjiang Uygur Autonomous Region in September. (Photo: China News Service/ Zhang Jiangang)

Migratory birds are seen at a wetland on Balikun grassland in northwest China's Xinjiang Uygur Autonomous Region in September. (Photo: China News Service/ Zhang Jiangang)