A group of bar-headed geese fly over Dragon King Pool park in Lhasa, southwest China's Tibet Autonomous Region, Dec. 25, 2017. The park is home to several species of migratory birds that come here during the winters. (Xinhua/Liu Dongjun)

Photo taken on Dec. 25, 2017 shows the migratory birds flying and swimming at Dragon King Pool park in Lhasa, southwest China's Tibet Autonomous Region. The park is home to several species of migratory birds that come here during the winters. (Xinhua/Liu Dongjun)

Photo taken on Dec. 25, 2017 shows the migratory birds flying and swimming at Dragon King Pool park in Lhasa, southwest China's Tibet Autonomous Region. The park is home to several species of migratory birds that come here during the winters. (Xinhua/Liu Dongjun)

A black-headed gull flies over the water in Dragon King Pool park in Lhasa, southwest China's Tibet Autonomous Region, Dec. 25, 2017. The park is home to several species of migratory birds that come here during the winters. (Xinhua/Liu Dongjun)

Bar-headed geese fly over Dragon King Pool park in Lhasa, southwest China's Tibet Autonomous Region, Dec. 25, 2017. The park is home to several species of migratory birds that come here during the winters. (Xinhua/Liu Dongjun)

Photo taken on Dec. 25, 2017 shows the migratory birds swimming at Dragon King Pool park in Lhasa, southwest China's Tibet Autonomous Region. The park is home to several species of migratory birds that come here during the winters. (Xinhua/Liu Dongjun)