Wiggins, D. (2005, October 17). Harlequin Duck (Histrionicus histrionicus): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region.
Harlequin ducks (Histrionicus histrionicus) have been the focus of management actions due to concern over declining populations. Relative to other species of ducks, harlequin ducks occur at low population densities and exhibit high breeding site fidelity, low reproductive rates, and delayed reproduction. All of these traits contribute to making harlequin duck populations particularly slow to recover from habitat degradation or loss, or other factors. The species apparently bred in small numbers in Colorado in the late 1800s but subsequently became extirpated there, likely as a result of habitat degradation related to mining activities (e.g., timber harvesting, contamination of water supplies). More recently, harlequin ducks have disappeared from former breeding sites in Idaho and Montana.
The primary factors thought to be responsible for local declines in the number of harlequin ducks are the degradation of breeding streams, human disturbance during the breeding season, and, in some areas, mortality due to hunting during the winter season.