Swans fly over Qinghai Lake, China's northwest Qinghai Province, Dec.12, 2010.Thanks to the improving environment of Qinghai Lake area, a state natural reserve, over 5,000 whooper swans came to spend winter here, which is the largest number of its yearly record. Qinghai Lake has actually become a "Swan Lake" on the Qinghai-Tibet Plateau. [Xinhua]