Black-necked Swan

The black-necked swan, Cygnus melancoryphus, is a striking species of waterfowl belonging to the tribe Cygnini. As the largest waterfowl native to South America, it presents a majestic figure with adults measuring between 102 to 124 cm in length and boasting a wingspan of 135 to 177 cm. Males are heavier, weighing 4.6 to 8.7 kg, while females tip the scales at a slightly lighter 3.5 to 4.4 kg. Both sexes share a similar appearance with pristine white body plumage contrasted by a black neck and head, the latter adorned with a white eye stripe. A distinctive red knob sits at the base of their bill, a feature absent in juveniles, who sport a grayish hue and acquire the knob in their third or fourth year.

Identification Tips

When identifying the black-necked swan, look for the unique combination of its black neck and head with the contrasting white body. The red knob at the bill's base is a clear marker, as is the white eye stripe in adults. Juveniles can be distinguished by their grayish color and lack of the red knob.

Habitat

This species is found in a variety of wetland habitats, including freshwater marshes, swamps, shallow lakes, brackish lagoons, and sheltered coastal areas. It often resides near human settlements in mainland South America but avoids built-up regions in the Falkland Islands.

Distribution

The black-necked swan graces the southern reaches of South America, nesting from Tierra del Fuego northward to central Chile, Uruguay, and southern Brazil. In winter, it migrates north as far as São Paulo state in Brazil and is a permanent resident of the Falkland Islands. Occasional vagrants have been spotted on various sub-Antarctic islands.

Behaviour

Outside of the breeding season, the black-necked swan is mostly a silent creature. However, during breeding, it becomes more vocal, using soft, musical calls to communicate with its mate or challenge intruders. The species is believed to form long-term pair bonds, with both sexes contributing to nest building. Breeding season varies by location, with rainfall influencing the timing.

Song & Calls

During the breeding season, both male and female black-necked swans may be heard giving a soft, musical "Whee-whee-whee" call, with emphasis on the initial syllable. Males also produce a "hooee-hoo-hoo" sound. These calls serve to maintain pair bonds and ward off potential threats.

Breeding

The black-necked swan's breeding season is geographically variable, generally occurring from July to November. Nests are mounds of vegetation located on small islets or floating in reedbeds. Clutch sizes range from four to eight eggs, with males standing guard during the 34- to 36-day incubation period. In captivity, fledglings take flight approximately 100 days post-hatching.

Diet and Feeding

A vegetarian at heart, the black-necked swan feeds primarily on aquatic plants such as Chara and Potamogeton, as well as algae. It forages by dipping its head and neck into the water, surface feeding, and occasionally upending to reach deeper vegetation. During droughts, it may graze in meadows and pastures.

Conservation status

The IUCN has classified the black-necked swan as Least Concern, with a stable and widespread population. Although it faced historical threats from hunting, it has since recolonized areas in Chile from which it was previously extirpated. Some egg collecting and hunting persist, but the species enjoys protection in several Argentinian reserves, where the population is estimated at 50,000 individuals.