Nests along fast-moving rivers and mountain streams on rocky islands or banks. Streams are braided to reticulate with many riffles and rapids (Cassirer et al. 1993). Requires relatively undisturbed, low gradient, meandering mountain streams with dense shrubby riparian areas (greater than 50% streamside shrub cover), and woody debris for nesting and brood rearing; also needs mid-stream boulders or log jams and overhanging vegetation for cover and loafing; indicator of high water quality (Spahr et al. 1991). Sometimes nests beside mountain lakes and lake outlets. Nests in a hollow, usually under the cover of bushes within about 30 m of water; also in rock crevice among boulders, in rock cavity in cliff face, in a tree cavity (Cassirer et al. 1993), in a puffin burrow, or similar hidden site; occasionally on open tundra (Ehrlich et al. 1992). In coastal Alaska, uses streams with larger discharges, widths, estuary areas, and riparian zones (Crowley 1994, Crowley and Patten 1996).
Cassirer, E. F., A. Breault, P. Clarkson, D. L. Genter, R. I. Goudie, B. Hunt, S. C. Latta, G. H. Mittelhauser, M. McCollough, G. Schirato, R. L. Wallen. 1993. Status of harlequin ducks (Histrionicus histrionicus) in North America. Report of the Harlequin Duck Working Group. March 1993. 83 pp.
Crowley, D. W. 1994. Breeding habitat of Harlequin Ducks in Prince William Sound, Alaska. Master’s thesis, Oregon State Univ., Corvallis.
Crowley, D. W. and S. M. Patten, Jr. 1996. Breeding ecology of Harlequin Ducks in Prince William Sound, Alaska. Exxon Valdez Oil Spill/ Federal Natural Resources Damage Assessment Final Report (Restoration Study no. 71), Alaska Dept. Fish and Game, Anchorage.
Ehrlich, P.R., D.S. Dobkin, and D. Wheye. 1992. Birds in jeopardy: the imperiled and extinct birds of the United States and Canada, Including Hawaii and Puerto Rico. Stanford University Press, Stanford, California. 259 pp.
Spahr, R., L. Armstrong, D. Atwood, and M. Rath. 1991. Threatened, endangered, and sensitive species of the Intermountain Region. USDA USFS, Ogden, Utah.