Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)

Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)

Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)

Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)

Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)

Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)

Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)

Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)

Migratory birds are seen at the Longwangtan Park in Lhasa, southwest China`s Tibet Autonomous Region, Nov. 21, 2019. Many migratory birds, such as bar-headed geese and black-headed gulls, arrived in areas along the Lhasa river valley and the Yarlung Zangbo River to escape the cold. (Xinhua/Purbu Zhaxi)