The Harlequin Duck (Histrionicus histrionicus) is a small sea duck with a colorful and complex plumage pattern. The head and neck are dark slate blue with a large white crescent marking in front of the eye. A black crown stripe runs over the top of the head, and a black-bordered white collar distinguishes the head from the breast. The body is mostly a lighter slate blue color with chestnut sides. Adult female Harlequin Ducks are less colorful. They breed in cold and fast moving streams, and they nest in a well-concealed location on the ground near a stream. Their smoothly packed feathers trap ample air which insulate their bodies from cold water.