The black swan (Cygnus atratus) is a large waterbird, a species of swan which breeds mainly in the southeast and southwest regions of Australia. A New Zealand subspecies was apparently hunted to extinction by Māori, but the species was reintroduced to New Zealand in the 1860s. Within Australia they are nomadic, with erratic migration patterns dependent upon climatic conditions. Black swans are large birds with mostly black plumage and red bills. They are monogamous breeders that share incubation duties and cygnet rearing between the sexes.

Black swans were introduced to various countries as an ornamental bird in the 1800s, but have escaped and formed stable populations. A small population of black swans exists on the River Thames at Marlow, and near the River Itchen, Hampshire, there is also one on the River Tees near Stockton on Tees. Described scientifically by English naturalist John Latham in 1790, the black swan was formerly placed into a monotypic genus, Chenopis. Black swans can be found singly, or in loose companies numbering into the hundreds or even thousands. Black swans are popular birds in zoological gardens and bird collections, and escapees are sometimes seen outside their natural range.

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