Sentence:  The events of the last quarter of an hour , mysterious to any bird accustomed only to the predictable life of coop and barnyard , had overcome the doctor 's hen and she gave out a series of cackly wails , perhaps mourning her <WSD>nest</WSD> , but briefly enjoyed . 
Meaning of the word marked with <WSD> tags:  a structure in which animals lay eggs or give birth to their young