Histrionicus histrionicus

No subspecies are currently recognized. Formerly, Pacific (H. h. pacificus) and Atlantic (H. h. histrionicus) subspecies were identified (Brooks 1915), but evidence to maintain this distinction was lacking (Dickinson 1953, Palmer 1976) (Robertson and Goudie 1999).

Although still globally widespread, the Atlantic population may be reaching critically low levels and the Pacific population has experienced substantial declines. Harlequins may exhibit high breeding and wintering site fidelity and small local breeding populations, and are thus subject to local extirpations. Declining overall populations may provide little chance of recolonization.

Holarctic. Nesting occurs in Eurasia and two disjunct regions in North America. Pacific population breeds from western Alaska (see Johnson and Herter 1989 for details), northern Yukon, northern British Columbia, and southern Alberta south to Oregon, Idaho, Wyoming, and east of the Continental Divide in Montana (perhaps historically in California and Colorado). The Atlantic population breeds from Baffin Island (at least formerly), Greenland, and Iceland through central and eastern Quebec, eastern Labrador, northern Newfoundland (perhaps historically much more widely in the North Atlantic region). This duck occurs in summer in Mackenzie Valley and near Great Slave Lake, Northwest Territories. In the Palearctic, harlequin ducks breed in Iceland and Greenland, and from the Lena River in Siberia east to Kamchatka and south to northern Mongolia and the Kurile Islands (American Ornithologists Union 1983). During the nonbreeding season, harlequin ducks occur in Eurasia; Aleutian and Pribilof islands south to central California; southern Labrador, Newfoundland, Nova Scotia, south to Maryland (but mostly north of Cape Cod); accidental in Hawaii; they are much more abundant in the Aleutians than farther south in southwestern Canada and U.S. Pacific Northwest.

This species is represented by a large number of breeding and nonbreeding occurrences (subpopulations).

Threatened by habitat degradation in breeding and wintering areas including: destruction of riparian areas; destruction of watershed stability and stream flow regimes by mining, roads, and timber harvest; impoundments and diversions on breeding streams; destruction of food base via pesticides; shoreline development and activities on wintering and breeding areas; disturbance by recreational river users and hikers in breeding areas (Spahr et al. 1991). Mortality factors include: over-harvesting of remnant populations; oil and other contamination in coastal areas (Harlequin Duck Working Group 1993). Oil may chronically recontaminate birds and eliminate reproduction (Patten 1993).