"The White Heron" is a story based largely around the theme of women's liberation.
While yes, it is a story about protecting nature and the beautiful things within it, the freedom of the white heron is also a metaphor for womanly freedom and youth. Remember that hunters often kill and preserve the animals the things they catch, usually through taxidermy, which is an apt description for the way wives were treated around 1886. The wife was subservient to the man, often there to look pretty and be a status symbol, but not do much else, not unlike an exotic stuffed bird.
Think about how this can relate back to Sylvia's free-spirited nature.