'Polish swan'. Knopsvane (Mute Swan, Cygnus olor)

Here four typical grey downy feathered cygnets and one white feathered: The latter is often called a "Polish swan", and it's caused by a recessive gene (like blue eyes or blond hair) so if both parents carry it then on average one in every four offspring will have two of them and will therefore be white from birth.
Gedser Sønder Boulvard 16/08 2015
Copyright © Louis A. Hansen