For most of the last century, one of the rarest birds in America made its home inside a mistake. The Ridgway's rail, a shy, chicken-sized marsh bird found nowhere on Earth but the reedy edges of San Francisco Bay, had quietly come to depend on an East Coast cordgrass never meant to grow on the West Coast at all. So when conservationists finally won their two-decade war against that invasive plant, the ending should've been simple: weed gone, bird saved, headline written.
