Abstract: Arctic shorebirds can travel tens of thousands of kilometers every year as they fly along intercontinental flyways from their southern wintering grounds to their remote, harsh breeding sites. How these birds solve the navigational and physiological constraints has been largely answered, but why they migrate is still a question with many possible answers (1). On page 326 of this issue, McKinnon et al. (2) present a continent-wide study that points to predation as a driving mechanism for migration. The study also elucidates the role of predation in shaping Arctic terrestrial biodiversity. Predation pressure falls with increasing latitude, helping to explain why many birds migrate as far north as the high Arctic. Predation pressure falls with increasing latitude, helping to explain why many birds migrate as far north as the high Arctic.