Sentence:  When one <WSD>approaches</WSD> the nest of this species, the male exhibits the greatest anxiety respecting its safety, passes and repasses, fluttering and snapping its bill within a few feet, as if determined to repel the intruder. 
Meaning of the word marked with <WSD> tags:  To come near to in place, time, character(,) or value; to draw nearer to.