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This sea duck occupies a niche that is unique among North American waterfowl. Along with the American Dipper (Cinclus mexicanus), the Harlequin Duck uses clear, fast-flowing rivers and streams for breeding and is able to move swiftly and with great agility in turbulent white water, diving to river bottoms to pick larval insects from rocky substrates. After breeding, individuals migrate to the coasts of North America and Greenland, where they occupy the shallow intertidal zones of rocky coastlines. They forage close to shore and consume a varied diet, including amphipods, snails, small crabs, barnacles, fish roe, and other small food items.
Males wear a striking breeding plumage that is slate blue with bold white, black, and chestnut markings. Their behavior is quite different from that of most other ducks. Harlequin Ducks squeak when engaged in behavioral interactions, a distinctly unducklike sound and the source of one of their local names, sea mice. Their ability to swim and feed among the boulders of a raging river is unmatched. In winter they are usually found close to shore, feeding in raging surf or loafing on rocks. They are relatively tame and can be approached closely in many areas. Their name derives from a character of traditional Italian comedy and pantomime, the harlequin, who appeared in costumes of multicolored triangular patches and displayed histrionics (tricks).
There are various serious threats to Harlequin Duck populations. Overhunting, disturbance, and habitat loss have likely played roles in declines in numbers. Until recently, little was known about the ecology of this species. This lack of knowledge has changed in the last 10 years, beginning with the 1990 listing of the East Coast population of Harlequin Ducks as Endangered in Canada. The historical population size of Harlequin Ducks on the East Coast of North America is under debate, but it was probably never large (<10,000), and the current wintering population is probably no greater than 1,500 birds. Research efforts have been launched on both coasts of North America to understand the life history, population status, and movements of many Harlequin Duck populations, including large-scale coordinated banding programs. Important studies on breeding ecology include Kuchel 1977, Dzinbal 1982, Wallen 1987, Crowley 1994, Cassirer et al. 1996, Bruner 1997, MacCallum and Bugera 1998, and Smith 1999a, 1999b on the West Coast of North America and Brodeur et al. 1998, 1999, Rodway 1998a, 1998b, and Rodway et al. 1998 on the East Coast. Molting and wintering ecology have been examined extensively in British Columbia (Vermeer 1983, Savard 1988a, Cooke et al. 1997, Gowans et al. 1997, Robertson et al. 1997a, 1997b, 1998a, 1998b, 1999, in press, Vermeer et al. 1997, Breault and Savard 1999, Goudie 1999) and in Newfoundland (Goudie and Ankney 1986, 1988). Migration routes have been established by satellite telemetry (Brodeur et al. 1998, 1999). It is hoped that this research effort will help provide the information needed to better conserve this engaging species in the future.