Swans frolic at a wetland in Wenquan County, northwest China's Xinjiang Uygur Autonomous Region, Dec. 29, 2012. Many migrant birds have come here for the winter. [Xinhua]

Swans swim at a wetland in Wenquan County, northwest China's Xinjiang Uygur Autonomous Region, Dec. 29, 2012. Many migrant birds have come here for the winter. [Xinhua]

Swans fly at a wetland in Wenquan County, northwest China's Xinjiang Uygur Autonomous Region, Dec. 30, 2012. Many migrant birds have come here for the winter. [Xinhua]

Swans swim at a wetland in Wenquan County, northwest China's Xinjiang Uygur Autonomous Region, Dec. 30, 2012. Many migrant birds have come here for the winter. [Xinhua]

Swans swim at a wetland in Wenquan County, northwest China's Xinjiang Uygur Autonomous Region, Dec. 30, 2012. Many migrant birds have come here for the winter. [Xinhua]

Swans fly over a wetland in Wenquan County, northwest China's Xinjiang Uygur Autonomous Region, Dec. 30, 2012. Many migrant birds have come here for the winter. [Xinhua]