A whooper swan flies over sea surface in Rongcheng City, east China's Shandong Province, Feb. 2, 2013. Thousands of whooper swans flying from Siberia and Lake Baikal chose to spend winter in Rongcheng thanks to its comfortable ecological environment. (Xinhua/Li Ziheng) 

Whooper swans look for food on a wetland in Rongcheng City, east China's Shandong Province, Feb. 2, 2013. Thousands of whooper swans flying from Siberia and Lake Baikal chose to spend winter in Rongcheng thanks to its comfortable ecological environment. (Xinhua/Li Ziheng) 

Whooper swans fly over sea surface in Rongcheng City, east China's Shandong Province, Feb. 2, 2013. Thousands of whooper swans flying from Siberia and Lake Baikal chose to spend winter in Rongcheng thanks to its comfortable ecological environment. (Xinhua/Li Ziheng) 

A whooper swan flies over sea surface in Rongcheng City, east China's Shandong Province, Feb. 2, 2013. Thousands of whooper swans flying from Siberia and Lake Baikal chose to spend winter in Rongcheng thanks to its comfortable ecological environment. (Xinhua/Li Ziheng) 

Whooper swans frolic on a wetland in Rongcheng City, east China's Shandong Province, Feb. 2, 2013. Thousands of whooper swans flying from Siberia and Lake Baikal chose to spend winter in Rongcheng thanks to its comfortable ecological environment. (Xinhua/Li Ziheng)