The black-necked swan (Cygnus melancoryphus) is a species of waterfowl in the tribe Cygnini of the subfamily Anserinae. It is found in Argentina, Brazil, Chile, Uruguay, and the Falkland Islands.
Taxonomy and systematics
The black-necked swan has occasionally been placed by itself in the genus Sthenelides. Its closest relatives are the black swan (C. atratus) and mute swan (C. olor).
Distribution and habitat
The black-necked swan is found in the southern tier of South America. It nests from Tierra del Fuego north to central Chile, Uruguay, and Rio Grande do Sul in extreme southern Brazil. It withdraws from the southern half of Argentina in winter and is then found as far north as Brazil's São Paulo state. It is a year-round resident of the Falkland Islands. Vagrants have been found on Juan Fernández Island, the South Orkney Islands, the South Shetland Islands, and the Antarctic Peninsula. The population in this sanctuary has fluctuated widely over the years, reaching a low of 214 in January 2008 and a peak of 22,419 in May 2020 before plumbing to 2,782 in May 2022.
Behavior
Feeding
The black-necked swan's diet is almost entirely vegetarian. It feeds on aquatic plants like Chara, Potamogeton, Typha; algae such as Aphantotece and Rhyzoclonium; and presumably small numbers of aquatic invertebrates. In parts of Chile its principal food is Egeria densa. It forages mostly by immersing its head and neck and by surface feeding, but also upends to reach deeper. In times of drought it has been observed grazing in meadows and pastures. As on May 30, 2023, three more black-necked swans were found dead due to influenza H5N1 in Lagoa da Mangueira, Taim Ecological Station, Brasil.
Status and conservation
The IUCN has assessed the black-necked swan as being of Least Concern. It has a very large range, and though its population size is not known, it is believed to be stable. No immediate threats have been identified.-->