Sentence:  As the wildebeest shrinks, the circle of sated birds lounging in the short grass expands. With bulging <WSD>crops</WSD>, the vultures settle their heads atop folded wings and slide their nictitating membranes shut. 
Meaning of the word marked with <WSD> tags:  A pouch-like part of the alimentary tract of some birds (and some other animals), used to store food before digestion, or for regurgitation; a craw.