Swans fly over a wetland in Sanmenxia, central China's Henan Province, Nov. 22, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Hao Yuan/Xinhua]

Swans are seen at a wetland in Sanmenxia, central China's Henan Province, Nov. 22, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Wang Ding/Xinhua]

Swans are seen at a wetland in Sanmenxia, central China's Henan Province, Nov. 23, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Wang Ding/Xinhua]

Swans fly over a wetland in Sanmenxia, central China's Henan Province, Nov. 23, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Hao Yuan/Xinhua]

Swans are seen at a wetland in Sanmenxia, central China's Henan Province, Nov. 23, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Wang Ding/Xinhua]

Swans are seen at a wetland in Sanmenxia, central China's Henan Province, Nov. 22, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Wang Ding/Xinhua]

Swans fly over a wetland in Sanmenxia, central China's Henan Province, Nov. 23, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Wang Ding/Xinhua]

Swans are seen at a wetland in Sanmenxia, central China's Henan Province, Nov. 22, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Hao Yuan/Xinhua]

A swan is seen at a wetland in Sanmenxia, central China's Henan Province, Nov. 23, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Hao Yuan/Xinhua]

Swans fly over a wetland in Sanmenxia, central China's Henan Province, Nov. 23, 2022. A large number of migratory swans flied to the Yellow River wetland in Sanmenxia to spend winter. [Photo by Wang Ding/Xinhua]