The Harlequin Duck, Histrionicus histrionicus is a small sea duck.
Adult males are slate blue with chestnut sides and white markings including a white crescent at the base of the bill. Adult females are less colourful, with brownish-grey plumage and a white patch on the head around the eye. Both adults have a white ear patch.
These birds feed by swimming under water or diving. They also dabble. They feed on molluscs, crustaceans and insects.
The eastern North American population is declining and is considered endangered. Possible causes include loss of habitat due to hydroelectric projects and loss of life due to oil spills near coastal areas.