A swan of southern South American wetlands. Adults have a white body with a black head and neck.
Adults have a conspicuous red knob at the base of a bluish-grey bill. Young birds are pale grey-brown and have not yet developed a black neck.
Black-necked swans use seashells in coastal nests. At Caulín Bay in southern Chile, nests contained bivalve and gastropod shells alongside small branches, shrub leaves, grass and stones. Built directly on the ground, the nests were circular and cake-shaped. Incubating pairs plucked white down to cover the nest crown.
A 2021 paper reported surveys of eggs and cygnets at Caulín Bay, Chiloé Island, during August–November of 2011 and 2014. Researchers followed families quietly on foot, choosing routes according to tides and wind. On Lacaos Island, nests stood in grass or beside shrubs near the coast. Additional observations with binoculars and a telescope recorded nesting beginning around July and hatching from mid-September to mid-December. Families with cygnets also gathered near streams entering the bay and the Huenque River estuary, where they drank freshwater. These coastal families moved between terrestrial nesting places and waters receiving freshwater.
An extinction-risk assessment has not been added yet.
The Caulín Bay breeding study calls for further investigation of factors affecting black-necked swan cygnet survival in marine wetlands. Its authors identify strong tidal currents along routes between island nests and freshwater areas, and the effects of seawater salinity, as subjects needing investigation. They also recommend continuing work on nesting and ecological interactions, choosing questions that support local wetland management and conservation. The proposed research would connect understanding of nesting places with the waters used by families raising young.