America’s northern border with Canada encompasses a remarkable range of habitats and weather extremes, from desert to tundra, grassland to rainforest, ocean to lake. They are home to epic migrations and a diversity of wildlife, where, for much of the route, nature’s inhabitants are only constrained by the challenges of the terrain and the changing seasons. But as we follow a year in the northern borderlands, we discover that even in the absence of a physical border, the political boundary poses many problems for wild residents.