Photo taken on Jan. 4, 2019 shows white swans rest at the Yellow River wetland in Sanmenxia, central China's Henan Province. White swans have flown from Siberia to the Yellow River wetland to spend winter. (Xinhua/Wang Ding)

Photo taken on Jan. 3, 2019 shows white swans at the Yellow River wetland in Sanmenxia, central China's Henan Province. White swans have flown from Siberia to the Yellow River wetland to spend winter. (Xinhua/Zhu Xiang)

Photo taken on Jan. 4, 2019 shows a white swan at the Yellow River wetland in Sanmenxia, central China's Henan Province. White swans have flown from Siberia to the Yellow River wetland to spend winter. (Xinhua/Wang Ding)

Photo taken on Jan. 4, 2019 shows white swans at the Yellow River wetland in Sanmenxia, central China's Henan Province. White swans have flown from Siberia to the Yellow River wetland to spend winter. (Xinhua/Zhu Xiang)

Photo taken on Jan. 3, 2019 shows white swans at the Yellow River wetland in Sanmenxia, central China's Henan Province. White swans have flown from Siberia to the Yellow River wetland to spend winter. (Xinhua/Wang Ding)

Photo taken on Jan. 4, 2019 shows white swans rest at the Yellow River wetland in Sanmenxia, central China's Henan Province. White swans have flown from Siberia to the Yellow River wetland to spend winter. (Xinhua/Wang Ding)

Photo taken on Jan. 3, 2019 shows white swans at the Yellow River wetland in Sanmenxia, central China's Henan Province. White swans have flown from Siberia to the Yellow River wetland to spend winter. (Xinhua/Wang Ding)

Photo taken on Jan. 3, 2019 shows white swans at the Yellow River wetland in Sanmenxia, central China's Henan Province. White swans have flown from Siberia to the Yellow River wetland to spend winter. (Xinhua/Zhu Xiang)