Adult males have a rust-red body, a blue bill, and a white face with a black cap. Adult females have a grey-brown body with a greyish face with a darker bill, cap and a cheek stripe.
Their breeding habitat is marshy lakes and ponds throughout much of North America. They nest in dense marsh vegetation near water. Pairs form each year.
They are migratory and winter in coastal bays and unfrozen lakes and ponds.
These birds dive and swim underwater. They mainly eat seeds and roots of aquatic plants, aquatic insects and crustaceans.
As a result of escapes from wildfowl collections, they are now established in Great Britain, from where they have spread widely into Europe. This duck's aggressive courting behaviour and willingness to interbreed with the endangered native White-headed Duck, Oxyura leucocephala, of southern Europe has caused some concern.
Due to this, there is now a controversial scheme to extirpate the Ruddy Duck as a British breeding species.