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I was told the comparison of Great Egret & Intermediate Egret is look at the end of gape. In close examination, the bare skin of the Great Egret's gape line extends in a dagger shape behind the eye, while the Intermediate's is less pointed and ends below the eye. As you said the yellow leg does cast a suspecion of the identity.
Structurally I find Intermediate can look more like a grossly oversized Cattle Egret; the neck often looks rather thicker than Great. The length of the gape is diagnostic though, I think.
Bare-part colour can vary a lot seasonally.
Flickr pics: http://www.flickr.com/photos/72243477@N00/
I am really sure. The size is too big for any other white Ardea.
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