Vol. 45, No. 2
David M. Larson
Sabine’s Gull. Photograph by Gregory Smith (CC BY-SA 2.0)
The northern latitudes of the Earth were, during the recent ice ages, covered with ice and largely depauperate of birds. During the retreat of the ice masses, landmasses became more available to birds as plants and animals re-established suitable habitats. The last places to become free of the year-round ice were in the vast expanses of the high Arctic. Hence, birds that breed in the high Arctic are among the most newly settled species. Few of these birds brave the Arctic winter, so most are migratory, spending the Arctic winter in climes with more abundant food resources. Migratory seabirds nesting in the North American Arctic may have expanded their ranges from the Atlantic, Pacific, or the Old World Arctic.
While some of the migratory Arctic breeders have localized breeding grounds, many are circumpolar, with populations that breed in the New and Old World Arctic. The study of migratory connectivity of breeding with wintering populations seeks to establish both ecological and evolutionary trajectories of species, and the roles of migratory divides in speciation. Certain aspects of these questions have been addressed in prior “Gleanings” articles (Larson, 2014, 2015).