Iceland Gull is a medium-sized, white-headed gull that nests on scattered cliff colonies throughout coastal regions of the Canadian Arctic Archipelago (Northwest Territories and Nunavut) and Greenland. These gulls are distinguished from other gulls by their size, soft-part coloration of adults, in particular a purplish-red orbital ring in breeding condition, and breeding habitat. Pairs nest primarily on small rocky ledges and outcroppings of vertical sea cliffs, often in association with Glaucous Gull (Larus hyperboreus), and occasionally Common Raven (Corvus corax). A large coastal cliff colony on southern Baffin Island impressed Dewey Soper (1) to write, “The latter afforded a memorable sight as in a restless cloud they wheeled hysterically in dextrous evolutions against the bleak facade of the great promontory.”
The Iceland Gull is separated into three subspecies based predominantly on markings and patterning of primary feathers and mantle coloration of adults. While the breeding ranges of these subspecies approach closely or narrowly overlap, a precise definition being elusive, the primary wintering ranges are rather widely disjunct. Birds breeding along the west coast of Greenland south of 70°N and on the east coast of Greenland make up Larus glaucoides glaucoides; most but not all adult glaucoides lack patterning on their wings and have correspondingly light mantles. Birds breeding to the east, south, and southwest of Baffin Island, Digges Sound area, and west to eastern Southampton Island make up "Kumlien's Gull" (L. g. kumlieni): adults have highly variable wing-tip patterns, sometimes without pattern, others are similar to Glaucous-winged Gull (L. glaucescens). Mantles of kumlieni are usually darker than those of glaucoides. Birds breeding in scattered colonies in northwestern Greenland and in the Canadian Arctic Archipelago north and west of kumlieni are "Thayer's Gull" (L. g. thayeri). Iris color and speckling varies greatly in adult thayeri, even in the western part of the breeding range. The great majority of adults in the westernmost populations have more extensively patterned wing-tips and darker mantles than kumlieni.
The large majority of glaucoides winter in the Arctic on coastal regions of southwestern Greenland, in open leads in sea ice and in open-water polynyas. In all likelihood, many kumlieni also overwinter in the Arctic. Winter sight records of glaucoides and kumlieni in the United States, southern Canada, Iceland, the Faroes, and Europe are mostly immature birds in coastal regions. In contrast, most thayeri appear to winter in the coastal Pacific Northwest, much less frequently to the Great Lakes region, and only very casually on the East Coast, the continental interior, and Gulf Coast. There are polynyas in the western Arctic in winter, but it is not known whether a portion of thayeri, in particular birds from western populations, overwinter in the north.
The taxonomy of the Iceland Gull is confusing and has been much disputed. The Iceland Gull was formerly treated as two species, L. glaucoides and L. thayeri [Thayer’s Gull] (e.g., 2, 3), but the two were recently merged (4) based primarily on evidence of nonassortative mating between L. g. kumlieni and L. thayeri on eastern Baffin Island, eastern Southampton Island, and Digges Sound (5, 6, 7).
The Iceland Gull is among the least known of all North American gull species and few studies have been dedicated to their natural history. The paucity of basic information relates to the difficulty of studying a high-arctic, cliff-nesting species, the inaccessibility of northern wintering areas, and, for glaucoides in particular, its infrequent occurrence in the south. There are important summaries of known or presumed information on identification of glaucoides, kumlieni, and thayeri (8, 9, 10, 11), including caveats and cautions. Important information concerning arrival, breeding and departure times, habitat, and nest-site preferences is available from scattered localities throughout the Arctic (12, 13, 14, 15, 16, 17). Further study is needed on almost all aspects of the biology of this intriguing and enigmatic gull species.