The sound of the hunter whistling (in order to imitate a bird call) appears a few different times in the story, forming a motif. The first time Sylvia hears the whistle, she knows immediately that it's coming from a person rather than a bird:
Suddenly this little woods-girl is horror-stricken to hear, a clear whistle not very far away. Not a bird’s-whistle, which would have a sort of friendliness, but a boy’s whistle, determined, and somewhat aggressive.
It is notable that Sylvia experiences the whistle as “determined, and somewhat aggressive” rather than “friendly,” like the whistle of real birds. This establishes that the hunter’s whistle is a threat to the ecosystem of the woods (as he wants to kill the birds to stuff them and display them in his home), similar to how the human encroachment of industrialization more broadly poses a threat to the natural world.
The hunter’s whistle is mentioned two more times in the story—when Sylvia starts to develop feelings for the hunter, she “smiles with pleasure” when she and the hunter walk by “the place where she heard the whistle.” Later, after she refuses to take the hunter to the white heron and he begrudgingly leaves, she “hear[s] the echo of his whistle haunting the pasture path as she [comes] home with the loitering cow.”
Sylvia’s shifting relationship to the whistle—first it is aggressive, then pleasurable, then haunting—mirrors her relationship to the hunter himself. While she was afraid of him at first, she moves into desiring him and thus supporting him in his greed for nature, and then ultimately returns to her original sense of fear and concern over his intentions. At the end of the story, she has learned that hunters' intentions cannot be trusted and that she must protect nature from people like him.
