Swans rest on Heihe River of Gaotai County in Zhangye City, northwest China's Gansu Province, December 10, 2009. Heihe wetland in Zhangye City covers an area of about 2000 square kilometers and plays an important role in the migration of birds. [Xinhua]

Swans fly over Heihe River of Gaotai County in Zhangye City, northwest China's Gansu Province, December 10, 2009. [Xinhua]