Originally a bird from Australia, Black swans were introduced to various countries as an ornamental bird in the 1800's, but have escaped and formed stable populations throughout Europe.
1st, 2nd & 3rd photo: 4 Adult Black Swans together with several Mute Swans. Natuurplas Breeveld, Woerden, The Netherlands, 21 December 2010
4th photo: A juvenile. Eemnesserpolder, The Netherlands, 24 February 2006