Harlequin duck (Histrionicus histrionicus)

Physical characteristics

Males are vividly patterned with slate-blue, chestnut and white markings that form bold bars and patches; females are much plainer, with mottled brown tones and a distinctive white patch near the eye. This sexual dimorphism is typical of many ducks and reflects different roles: males advertise and defend, while females remain cryptic, especially during nesting. The male’s contrasting patterning can act as disruptive coloration, breaking up the outline of the body against complex backgrounds such as rippling water or rocky shorelines. Outside the breeding season males molt into a less conspicuous plumage, as is common among dabbling and diving ducks.

Distribution and habitat

Harlequin ducks breed in fast-flowing mountain streams and rivers across northern North America, Greenland, Iceland, and parts of Eurasia. In winter they congregate along rocky coasts and inshore waters, where they forage in surf and tidal pools. Populations are largely coastal in colder months but may be found inland where suitable turbulent streams occur. Their preference for rough water and wave-swept shores distinguishes them from many other duck species.

Behavior, diet and reproduction

Adapted to strong currents and breaking surf, harlequin ducks are agile divers that forage for aquatic invertebrates. Their diet typically includes crustaceans, mollusks, insect larvae and other small organisms scraped from stones and crevices. Breeding pairs nest close to fast streams, usually in sheltered vegetation or rock cavities; the female incubates the eggs and leads the young to water after hatching. Males may display territorial or courtship behaviors during the breeding season, and vocalizations include a high, thin call that has earned one of their common names, "squeaker."

Colors, signaling and ecology

Bright male colors serve multiple ecological and social functions. They may be selected by females as indicators of health or genetic quality, a process referred to as sexual selection. At the same time, conspicuous plumage and patterning help males assert territories or signal to rivals during the breeding season. The disruptive patterning of the male’s feathers also makes its silhouette harder to detect against variegated backgrounds like water and rocks. Only careful observation and experimental study can untangle the relative importance of these factors in any population.

Conservation and human interactions

Globally the species is not regarded as immediately threatened, but some regional populations have experienced declines. Sensitivity to oil pollution, coastal development, disturbance, and changes in freshwater stream habitats have prompted local conservation concern and monitoring. Protective measures include habitat preservation, pollution controls, and research on population trends. Observers and wildlife managers emphasize minimizing disturbance at breeding sites and reducing contamination of coastal feeding areas.

Further reading

• General accounts of sea ducks and species identification may be found in field guides under the entry for duck.
• Information on coastal ecology and marine wintering habitats is summarized in resources about the sea and rocky shore communities.
• For studies of mating systems and the evolution of plumage, see treatments of sexual selection.