The northward spread of the Herring Gull (Larus argentatus) into Iceland in the last several decades has resulted in extensive hybridization with the Glaucous Gull (L. hyperboreus; Ingolfsson, 1970). Hybridization between these species in North America is almost unknown, although two apparent hybrids have been collected in New Jersey in recent years (Jehl and Frohling, 1965). In the eastern Canadian arctic, where the species are widely sympatric, interbreeding is unrecorded. In the western Canadian arctic and in Alaska occasional hybridization has been inferred (Dwight, 1925; Ingolfsson, 1970). Because hybrids may provide evidence about the relationships and evolutionary history of species, they are of particular interest to biologists.