The speaker is walking through a field at the end of winter and noticing what has been left behind. The goldenrods still hold the empty homes of wasps, and the split milkweed pods stand in clusters on their stalks. The speaker describes these pods as a "Baroque superfluity of arch and wing," as if the dried plants were ornate, a bit showy, and no longer needed for anything. Everything in the first two stanzas is hollow, spent, and still.
Then a sound breaks in. A grouse drums somewhere in the woods, and the speaker is reminded of what "real wings can do." The milkweed only looks like it has wings, while the bird's wings actually beat. The drumming speeds up like a heartbeat, so the poem ends on life starting up again.
The mood is quiet and observant, a little wistful at first, then alert and hopeful. The speaker seems glad to be shaken out of looking at dead things and toward spring.