Photo taken on Dec. 18, 2018 shows black-necked cranes in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)

Photo taken on Dec. 18, 2018 shows a black-necked crane in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)

Photo taken on Dec. 18, 2018 shows black-necked cranes in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)

Photo taken on Dec. 18, 2018 shows black-necked cranes in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)

Photo taken on Dec. 18, 2018 shows black-necked cranes in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)

Photo taken on Dec. 18, 2018 shows black-necked cranes in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)

Photo taken on Dec. 18, 2018 shows black-necked cranes in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)

Photo taken on Dec. 18, 2018 shows black-necked cranes in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)

Photo taken on Dec. 18, 2018 shows black-necked cranes in Linzhou County of Lhasa, capital of southwest China's Tibet Autonomous Region. Thousands of black-necked cranes have arrived here to spend the winter time. (Xinhua/Purbu Zhaxi)