Black-necked Swan

This striking and elegant waterfowl is immediately recognizable by its dramatic color contrast, featuring a pure white body that stands in stark opposition to its velvety black neck and head. It exhibits a body length ranging from 102 to 124 centimeters (40 to 49 inches) and a body mass of 4 to 6.7 kilograms (8.8 to 14.8 pounds) in adult males, with females being slightly smaller. Its bill is slaty gray and features a prominent, bright red fleshy caruncle at its base, which becomes larger in mature birds, especially males. A thin, delicate white stripe encircles the eye and extends backward towards the nape, while the short legs are a distinctive pale pink. Juvenile individuals lack the intense red caruncle and display a drabber greyish-brown plumage on their necks and heads.

Geographical distribution: It is native to the southern cone of South America. Its primary breeding range encompasses Argentine and Chilean Patagonia, the Falkland Islands, and Tierra del Fuego. During the austral winter, southern populations undertake significant migrations northward, dispersing across central Chile, northern and central Argentina, the entirety of Uruguay, and southernmost Brazil (particularly within the state of Rio Grande do Sul). Vagrant individuals are occasionally reported in Paraguay, southeastern Bolivia, and even oceanic islands near the Antarctic Peninsula.

Habitat: This species primarily frequents shallow, calm aquatic environments. It prefers freshwater lakes, brackish lagoons, marshes, coastal estuaries, and peat bogs with abundant submerged and emergent aquatic vegetation. Deep water bodies or fast-flowing river channels are generally avoided, as they require quiet, shallow zones where they can easily forage by reaching the bottom with their necks and find shelter within dense reed beds.

Feeding: It is an obligate herbivore whose diet consists almost exclusively of submerged aquatic macrophytes and algae. It feeds by dipping its long neck underwater or tipping its body forward (up-ending) to filter organic material from the substrate. Preferred plant genera include Ruppia, Myriophyllum, and Chara. While foraging, it incidentally ingests small aquatic invertebrates, larvae, and organic debris attached to the plants, which provides supplemental nutrients.

Behavior: Highly gregarious outside the breeding period, this swan forms impressive wintering flocks that can number in the thousands. Due to its heavy build, it requires a long, flapping run across the water´s surface to take flight, but once airborne, it is a swift and enduring flyer. It is remarkably quiet compared to northern hemisphere swans, communicating via soft, high-pitched whistling calls. A notable parental behavior is carrying young cygnets on their backs, which keeps the chicks warm and dry while keeping them safe from aquatic predators.

Nesting: The breeding season commences during the late austral winter, between July and September. Strongly monogamous pairs defend nesting territories and construct a large, bulky nest of reeds, rushes, and other aquatic vegetation, usually hidden within reed beds or built on small islands. The female lays a clutch of 4 to 7 cream-colored eggs, which she incubates alone for approximately 34 to 36 days while the male guards the surrounding territory. Once hatched, the highly precocial chicks leave the nest almost immediately, but remain under close parental supervision and protection for several months.

Conservation status: It is evaluated as Least Concern (LC) on the IUCN Red List, owing to its vast distribution range and overall stable populations. Nevertheless, regional populations face ongoing threats from wetland degradation, chemical pollution of water basins—which decimates their food supply—recreational hunting, and lead poisoning resulting from the ingestion of lead shot found in wetland sediments.