Except when breeding, Harlequins are gregarious, feeding, molting and wintering on traditional grounds in flocks. Harlequins winter along the rugged coasts of southern Newfoundland, the Atlantic Coast of Nova Scotia, in the Bay of Fundy off New Brunswick, the Gulf of Maine to as far south as the mouth of the Chesapeake Bay. The eastern population of the Harlequin Duck was listed as endangered by the Committee on the Status of Endangered Wildlife in Canada in 1990 because its numbers have declined to a point below minimum viable population size. Their habit of staging, molting, and wintering in flocks in traditional areas leaves the species vulnerable to human disturbance, oil pollution, and interruption of the food supply. Its breeding habitat is threatened by a variety of disturbances including hydroelectric development, forestry, insect control programs, low-level military flying, resource development and increased access by humans.
Hunters can help by properly identifying their targets before shooting.
The prevention of oil and chemical spills in Atlantic Canadian waters is important to ensure the protection of traditional wintering areas.