Males have entirely black bills. Females and juveniles have some orange coloration at the base of the bill and on the lower mandible. Females have dark brown eyes. The Hooded is the only merganser whose range is entirely restricted to North America. They can be divided into western and eastern populations.
Western birds breed from Montana and Oregon north to southern Alaska.
They winter along the Pacific coast from southern Alaska to California. The eastern population has a much larger range. They breed from the eastern half of southern Canada south through the United States from the Northern Great Plains and Mississippi Valley east to the Atlantic. The southern edge of their breeding range stops just short of the Gulf Coast. Breeding eastern Hooded Mergansers reach their highest concentration in the Great Lakes Region.