Resting whooper swans flutter at the Yellow River wetland in Pinglu County, north China's Shanxi Province, Feb. 1, 2010. The World Wetlands Day 2010 is celebrated on Feb. 2. (Xinhua/Xue Jun)

 

Whooper swans frolic at the Yellow River wetland in Pinglu County, north China's Shanxi Province, Feb. 1, 2010. (Xinhua/Xue Jun)

 

Resting whooper swans are seen at the Yellow River wetland in Pinglu County, north China's Shanxi Province, Feb. 1, 2010.(Xinhua/Xue Jun)

 

Whooper swans are seen at the Yellow River wetland in Pinglu County, north China's Shanxi Province, Feb. 1, 2010. (Xinhua/Xue Jun)

 

Whooper swans forage for food at the Yellow River wetland in Pinglu County, north China's Shanxi Province, Feb. 1, 2010.(Xinhua/Xue Jun)

 

Resting whooper swans are seen at the Yellow River wetland in Pinglu County, north China's Shanxi Province, Feb. 1, 2010. (Xinhua/Xue Jun)

 

Resting whooper swans are seen at the Yellow River wetland in Pinglu County, north China's Shanxi Province, Feb. 1, 2010.(Xinhua/Xue Jun)