Coscoroba Swan

The coscoroba swan is one of South America's largest waterfowl, yet smaller than the true swans, making it the smallest swan species. It looks somewhat goose-like, with a duck-like bill, a shorter neck than other swans and bright pink legs and feet. Adults are completely white apart from black tips on the outer six primary feathers. Its longer legs let it walk easily on land and take off quickly from land or water. It lives on well-vegetated lagoons and freshwater swamps in Argentina, Bolivia, Brazil, Chile, Paraguay, Uruguay and the Falkland Islands, feeding on plants, small invertebrates and small fish, and it often feeds alongside black-necked swans.

About the coscoroba swan

The coscoroba swan is a white South American waterfowl in the duck, goose and swan family, Anatidae. It is the only species in its genus and the smallest bird called a swan, and a 2014 genetic study suggested a close relationship with the Cape Barren goose. It lives in wetlands from southern Brazil to Tierra del Fuego.

Coscoroba coscoroba sits in an awkward spot on the family tree. Following that genetic work, one major checklist groups it with the Cape Barren goose in their own tribe, placed as an early branch before the true swans of the genus Cygnus and all other geese. Other checklists list the coscoroba next to the true swans instead. Either way, it is the only member of the genus Coscoroba and has no subspecies.

To the eye, the bird looks like a cross between a swan, a goose and a duck. It has a shorter neck than other swans, a goose-like body and a broad, duck-like bill. Adults are entirely white except for black tips on the outer six primary feathers. The legs and feet are bright pink, a strong contrast with the white plumage.

One small detail separates it from every true swan. In the coscoroba, feathers grow right up to the base of the bill, which is not the case in black swans, mute swans and the other true swans.

The sexes look alike, but males are larger. A male can weigh up to 5.4 kg (12 lb), with a wing 44 to 49.8 cm (17.3–19.6 in) long; a female's wing measures 41.5 to 47.7 cm (16.3–18.8 in). Birds in southern Brazil run noticeably smaller, with male wings of only 37.5 to 39 cm (14.8–15.4 in). Even at full size, the coscoroba is among the largest waterfowl in South America while still being smaller than any true swan.

Its build also changes how it moves. Longer legs and a more upright posture let it walk easily on land, and it can take off from land or water much faster than true swans can.

Behavior and diet

The coscoroba's diet has not been studied in detail, but it appears to eat aquatic plants, some land plants, small aquatic invertebrates and small fish. Most feeding happens while the bird swims or wades in shallow water. Unlike other swans, it rarely upends, the head-down, tail-up posture swans use to reach deeper food. It also grazes on land, and it often feeds alongside black-necked swans.

Pairs stay together for the long term. The breeding season falls in the southern spring, though timing varies by region: May to October in northern Argentina, July to December in Chile, and July and August in southern Brazil. Both members of the pair build the nest, sometimes with the male doing most of the work. The nest is a mound of vegetation lined with soft grass, placed on a small islet, half-floating in a reedbed, or in long grass close to water.

A clutch holds 4 to 9 oval eggs, each about 167 g (5.9 oz) and roughly 82–94.5 mm (3.2–3.7 in) long. The female incubates for about 35 days while the male stands guard. Chicks hatch in greyish-white down with a black cap, and both parents raise them. Young birds fledge at 13 to 14 weeks and reach adult size at about 8 months. Double-brooding has been recorded, with a female starting a second clutch 40 to 50 days after the first one hatched. Young coscorobas may stay with their parents until they are a year old, and up to two years in captivity.

The name comes from the bird itself. Its main call is a loud "cos-cor-oo," used mostly as a threat to intruders. Mates keep in touch with a single hooting note, and immature birds make loud chirps and trills. In captivity, coscoroba swans can live about 20 years.

Range and habitat

The coscoroba swan lives year-round in central Argentina and along the coast of Uruguay and southern Brazil. It also breeds farther south, from southern Chile and Argentina down to Tierra del Fuego and occasionally the Falkland Islands, but leaves those areas in winter. In the colder months its range spreads north to central Chile, northern Argentina, Paraguay, Uruguay and southern Brazil. Wandering birds have turned up in Bolivia and in parts of Brazil north of the usual range.

Its preferred habitat is well-vegetated lagoons and freshwater swamps, and it sometimes uses human-made reservoirs. It is mainly a lowland bird, though there are scattered records up to 1,300 m (4,300 ft) and at least one at 2,000 m (6,600 ft).

Numbers vary widely across that range. The bird is fairly common in Argentina, uncommon in Paraguay and Uruguay, rare in Chile, and its status in Brazil is uncertain.

Coscoroba swan vs true swans

The coscoroba is called a swan, but several traits set it apart from the true swans of the genus Cygnus, including the black swan, mute swan and trumpeter swan.

Conservation status

The coscoroba swan is rated Least Concern on the IUCN Red List, in a 2016 assessment by BirdLife International. It has a large range, and its population of about 6,700 to 17,000 mature individuals is thought to be stable. No immediate threats have been identified.

The greatest threat appears to be the loss of temperate marshes to urban growth and farming. The bird feeds and nests in vegetated lagoons and swamps, so those wetlands are the habitat that matters most for its future.