On the surface "A White Heron" is about a little girl who becomes tempted by money, but eventually decides that she'd rather allow a bird to live. Upon further analysis, however, it becomes clear that the story is much more than it seems. Sylvia, also known as Sylvy, is a young girl who used to live in a big, crowded town, but now lives separate from all that on a farm, surrounded by nature. The story even refers to Sylvy as a "woods-girl," implying that she has now become a part of her wild environment.
The hunter is never named but is given makeshift titles like "the ornithologist," "the stranger," and even "the enemy" at one point. This man butts his way into Sylvy and her grandmother's life quite rudely, in my opinion, and imposes upon them for food and a place to spend the night. He informs them that he collects and performs taxidermy on birds, with a special emphasis on rare ones. He then proceeds to ask them if either of them might have seen an uncommon white heron bird nearby and offers them ten dollars if they can find it for him.
Thus begins Sylvy's dilemma. She thinks she knows where the heron has made its nest and she is instantly enticed by the prospect of ten dollars, which would be a great deal of money to her at the time. She does not tell the hunter right away where the bird might be, as some children might have done out of excitement, because she is uncertain of the precise location and is implied to be more than a little shy. That night she goes out searching for the bird, the thought of the money urging her on. After an arduous climb that almost certainly put her life at risk, she catches a glimpse of the bird. But when Sylvy returns home she refuses to tell the hunter anything.
Something Sylvy saw when she searched for the heron's nest that night made her change her mind about wanting the money. The obvious assumption is that she was awed by the beauty and wonder of nature and realized that the life of a rare and lovely bird wasn't worth money that wouldn't even last. However, the story means a great deal more when the parallels are taken into account.
Like the heron, Sylvy is a creature out of the environment she was born in, inherently wild, and pursued in some fashion by the hunter. When she first encounters the hunter she is instantly wary and afraid of him, much like a wild animal might be. She even remarks that his bird whistle is "somewhat aggressive."
The hunter represents the cold, hard town that Sylvy came from and the obsession with power and possession in a rapidly modernizing world. He symbolizes all the people, perhaps men in particular, who might come to Sylvy throughout her life and try to buy, possess, or keep her in some way. He also represents how greed can lead to the needless destruction of nature.
Sylvy, on the other hand, is nature. An untamable, un-buyable, and increasingly-rare being that is better left alone.