In late May - early June the ducks move inland to breed, usually already in pairs. Harlequins generally seek rapidly flowing streams and rivers for nesting and rearing young, most nests are built very close to the water on the ground in dense vegetation, among tree roots, or in rock crevices. The female lays 5-6 pale, buff-colored eggs, at which time the male abandons the female. Incubation takes 30 to 32 days, longer than any other sea duck. The newly hatched chicks are very agile and are led to secluded streams by the female within 24 hours of hatching where they learn to find aquatic insects and larvae. The young are able to fly when they are about 40 to 50 days old and are apparently brought to the coast only when fledged.
Sexually dimorphic. The males are dark blue gray with a white face between the eyes. They have black bordered white markings including a spot over the ear, a streak on the side of the neck and from the shoulder to the breast. The black crown is highlighted by rust and there is a large rust patch on the flank. Females are grayish black with light cheeks and a spot above the eye and over the ear. Harlequins usually molt around August when males lose most of their striking colors and the males and females are difficult to distinguish.
Morphology and Function
In the winter months Harlequins move to inshore marine waters, rocky shores and reefs; often perches on rocks for preening and sleeping. On the west coast harlequin ducks will often congregate at herring spawning areas prior to migration, where they feast on herring eggs.
Harlequin ducks are particularly vulnerable to oil spills because they are linked closely with intertidal habitats where oil washes up. Satellite telemetry has provided new information about this species wintering and breeding movements, along with studies of breeding ecology and the effects of human disturbances on harlequin populations.
Harlequins are quite vocal and the most common call is a mouselike squeak.The eastern populations of Harlequins are currently a Species of Concern.