The Harlequin Duck (Histrionicus histrionicus) is a small sea duck that can be found along rocky coastlines and fast-moving streams in North America. Adults are typically around 15 inches long and weigh between 1-2 pounds, with males being slightly larger than females. One of the most distinguishing field marks of the Harlequin Duck is the striking coloration of its breeding plumage, which features a deep blue-gray head with white stripes and bold chestnut sides. Non-breeding adults and juveniles have a more muted plumage with gray-brown heads and dusky sides.

During the breeding season, Harlequin Ducks can be found in swift-moving streams and rivers in Alaska, Canada, and the northwestern United States. After the breeding season, they migrate to the coastlines of western North America and can be found as far south as California. Some populations of Harlequin Ducks are known to migrate even farther south to winter along the coasts of Japan and Russia.

Harlequin Ducks are known for their ability to swim and dive in fast-moving water, and they feed on a variety of invertebrates and small fish. They are also known for their unique courtship behavior, which involves the males displaying for females by bobbing their heads, preening, and making a series of vocalizations.

While Harlequin Ducks are not considered endangered, their populations have declined in some areas due to habitat loss and pollution. Conservation efforts are underway to protect their breeding and wintering habitats, as well as to reduce the impact of human activities such as oil spills and development along coastal areas.

Overall, the Harlequin Duck is a fascinating and unique species of sea duck with striking coloration and impressive adaptations for living in fast-moving water. Its migratory habits and courtship behavior make it a fascinating subject for birdwatchers and wildlife enthusiasts alike.