The Yellow-billed Loon, known in Britain as the White-billed Diver, is a relatively rare bird nesting in arctic tundra regions of North America and Eurasia. First described by G. R. Gray in 1859, and named (G. adamsii) after the surgeon Dr. Adams (who collected the first specimen) aboard the H.M.S. Enterprise during that vessel's voyage through Bering Strait, this species is closely related to the Common Loon and often confused with it. Distinguished from the latter by bill shape and color, the Yellow-billed Loon breeds generally north of the range of its smaller and more widespread relative, although the two species overlap considerably on marine wintering grounds in the Pacific Northwest. Increasingly, however, the Yellow-billed Loon has been recorded wintering well inland in North America, a phenomenon that probably stems as much from improved information on field identification of loons in Basic plumage as from any shift in their range.
As a breeder, this is a bird of lakes and slow-moving rivers in low-lying tundra regions, almost entirely beyond the tree-line, where it nests on islands and shorelines and forages for fish and invertebrates in nearby waters. Often arriving before lake ice has fully retreated, it sometimes feeds at ice edge, even diving beneath the ice in pursuit of prey. A strongly territorial species, each pair defends its lake (or portion thereof) against intruding members of its own species, other loons, and even diving ducks. Parents share incubation duties and feeding of the chicks, which are brooded onshore when young.
Few ecological studies of this species have been conducted because of its remote breeding range and low population densities. Sjölander and Ågren ( Sjölander and Ågren 1978 ) described behaviors and calls during an 8 week study of renesting pairs at Alaktak, 80 km southeast of Barrow, AK. North ( North 1986a , unpubl. data) and North and Ryan ( North and Ryan 1988a , North and Ryan 1989 ) studied Yellow-billed Loon habitat use, foraging ecology, reproductive success, nest-site characteristics, and breeding season chronology. General observations on breeding biology were made by Sutton ( Sutton 1963b ), Parmelee et al. ( Parmelee et al. 1967 ), and Sage ( Sage 1971 ). Most other information on Yellow-billed Loon breeding biology and distribution comes from accounts of early expeditions to the arctic (e.g., Stone 1900 , Dixon 1916 , Bailey 1948 ) or from studies of habitats and other species (e.g., Manning et al. 1956 , Smith 1973c , Derksen et al. 1981 ).