The scene is small and quiet: someone stands on a cleared strip of land under powerlines, eating wild blueberries while fog pours through gaps in the hills below. The title tells us a wren is scolding, though the poem itself never mentions it again. That absence is part of the charm. We hear the bird only because the title points it out, the way you notice a sound once someone says it's there.
The most interesting moment is the phrase "this wren's powerline right-of-way." The speaker doesn't claim the spot as their own. A human-made corridor becomes the bird's territory, and the speaker is a visitor, maybe an unwelcome one, which would explain the scolding. The mood is relaxed and a little humble. The speaker seems content, absorbed in a simple pleasure, aware of the huge, slow movement of fog in the distance and the tiny, immediate business of picking berries. Grand and small things sit side by side without any fuss.