The story is told by an omniscient narrator who varies her proximity to and intimacy with the characters and events to direct the reader in their response to the story.
There are points where the narrative becomes Sylvia’s, the protagonist, and these points are at the height of the action and important events of the text. When Sylvia’s peace is interrupted by the stranger, the narration shifts to her perspective. Similarly, as she locates the heron’s nest and when she resolves to keep its location secret, the reader sees through Sylvia’s eyes.
The narrative shifts in the story have been an area for contention, praise and criticism. It is useful to have your own view on the effectiveness of Jewett’s technique.