Every spring the starlings gathered in the northwest corner of the marsh, their dark shapes clustered tight against the cold. By summer they had drifted to the center of the wetland, feeding in the warm shallows. But the autumn storm of that year was fierce — gale-force winds that drove the entire flock backward, all the way to their spring roost in the northwest. Come winter they pressed on again, scattering southeast as if the storm had never happened.