Whooper swans swim on a lake at Rongcheng National Nature Reserve in Rongcheng, east China's Shandong Province, Nov. 18, 2012. Thousands of swans chose to get through winter at the reserve. (Xinhua/Lin Haizhen)

Whooper swans fly from a lake at Rongcheng National Nature Reserve in Rongcheng, east China's Shandong Province, Nov. 18, 2012. Thousands of swans chose to get through winter at the reserve. (Xinhua/Lin Haizhen)

Whooper swans swim on a lake at Rongcheng National Nature Reserve in Rongcheng, east China's Shandong Province, Nov. 18, 2012. Thousands of swans chose to get through winter at the reserve. (Xinhua/Lin Haizhen)

A whooper swan sings on a lake at Rongcheng National Nature Reserve in Rongcheng, east China's Shandong Province, Nov. 18, 2012. Thousands of swans chose to get through winter at the reserve. (Xinhua/Lin Haizhen)