Photo taken on Nov. 23, 2017 shows reeds at Lalu wetland in Lhasa, southwest China's Tibet Autonomous Region. Lalu wetland national nature reserve, with an altitude of about 3,600 meters, covers an area of nearly 13 square kilometers. Over 5,000 birds of more than 20 species inhabit here throughout the year. In winter, dozens of species of migratory birds flew to the wetland. (Xinhua/Jigme Dorje)

Photo taken on Nov. 23, 2017 shows willow trees at Lalu wetland in Lhasa, southwest China's Tibet Autonomous Region. Lalu wetland national nature reserve, with an altitude of about 3,600 meters, covers an area of nearly 13 square kilometers. Over 5,000 birds of more than 20 species inhabit here throughout the year. In winter, dozens of species of migratory birds flew to the wetland. (Xinhua/Jigme Dorje)

Aerial photo taken on Nov. 23, 2017 shows Lalu wetland in Lhasa, southwest China's Tibet Autonomous Region. Lalu wetland national nature reserve, with an altitude of about 3,600 meters, covers an area of nearly 13 square kilometers. Over 5,000 birds of more than 20 species inhabit here throughout the year. In winter, dozens of species of migratory birds flew to the wetland. (Xinhua/Purbu Zhaxi)

Birds are seen at Lalu wetland in Lhasa, southwest China's Tibet Autonomous Region, Nov. 23, 2017. Lalu wetland national nature reserve, with an altitude of about 3,600 meters, covers an area of nearly 13 square kilometers. Over 5,000 birds of more than 20 species inhabit here throughout the year. In winter, dozens of species of migratory birds flew to the wetland. (Xinhua/Zhang Rufeng)

Bar-headed geese fly over Lalu wetland in Lhasa, southwest China's Tibet Autonomous Region, Nov. 23, 2017. Lalu wetland national nature reserve, with an altitude of about 3,600 meters, covers an area of nearly 13 square kilometers. Over 5,000 birds of more than 20 species inhabit here throughout the year. In winter, dozens of species of migratory birds flew to the wetland. (Xinhua/Zhang Rufeng)