By Tony Hisgett from Birmingham, UK (Black-necked Swan Uploaded by Magnus Manske) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
South America. Resident in Uruguay, southern Brazil and eastern Argentina and on the Falkland Is. Breeds in southern Argentina and winters in northern Argentina, Paraguay and southern Brazil.
Widely kept in collections. Available at £500 a pair in 2017. Far less frequent as an escape than the Black Swan and currently I can cite no instances