Coscoroba swan

Description

The coscoroba swan is among the largest waterfowl in South America, but smaller than the true swans, making it the smallest "swan" species. It is somewhat goose-like in appearance with a duck-like bill. It is shorter-necked than other swans. Unlike other swans, its feathers go straight to the base of the bill. The adults are completely white, except for black tips to the outer six primary feathers. They have bright pink legs and feet.

Their posture and longer legs allow the coscoroba swan to walk easily on land, this also lets them take off into flight quickly from land or water, much faster than the true swans.

The sexes are similar, but the male is larger. Males can weigh up to 5.4 kg (12 lb). The wing length of males is 44–49.8 cm (17.3–19.6 in) and in females 41.5–47.7 cm (16.3–18.8 in). Those in southern Brazil have differing measurements, the wings of males being 37.5–39 cm (14.8–15.4 in) and females 35–35.8 cm (13.8–14.1 in).

Distribution and habitat

The coscoroba swan is a year-round resident of central Argentina and along the Uruguay-southern Brazil coast. It also breeds, but does not winter from southern Chile and Argentina south to Tierra del Fuego and occasionally to the Falkland Islands. In winter, its range extends north to central Chile, northern Argentina, Paraguay, Uruguay, and southern Brazil. It has been recorded as a vagrant in Bolivia and at several locations in Brazil north of its usual limit. The coscoroba swan inhabits well-vegetated lagoons, freshwater swamps, and sometimes human-made reservoirs. It is mainly a bird of the lowlands, though there are scattered records as high as 1,300 m (4,300 ft) and at least one at 2,000 m (6,600 ft).

Behavior

Feeding

The coscoroba swan's diet has not been studied in detail, but it apparently feeds on aquatic and some terrestrial plants, small aquatic invertebrates, and small fish. It forages mainly while swimming or wading in shallow water and in contrast to other swans rarely upends. It also grazes on land. It often feeds with black-necked swans (Cygnus melanocoryphus).

Breeding

The coscoroba swan breeds in the local spring, which is May to October in northern Argentina, July to December in Chile, and July and August in southern Brazil. The species forms long-term pair bonds. Its nest is a mound of vegetation lined with soft grass constructed by both members (sometimes mainly the male) of a pair on a small islet, partially floating in a reedbed or long grass close to water. The clutch size is four to nine oval eggs that weigh about 167 g (5.9 oz) with dimensions of around 82–94.5 mm (3.23–3.72 in) in length and 52.9–67 mm (2.08–2.64 in) in width. Males guard females during the incubation period of about 35 days. The chicks hatch with grey-ish white down and a black cap. They are cared for by both adults and fledge at 13–14 weeks of age, and reach adult size after about 8 months. Double-brooding has been documented, where the female began incubating a second clutch 40–50 days after hatching the first. They sometimes stay with adults until they are a year old, even up to two years in captivity. In captivity, coscoroba swans can live 20 years.

Vocalization

The coscoroba swan makes an onomatopoeic "cos-cor-oo", usually as a threat to intruders. They also make a "monosyllabic hooting note" as a contact call between mates. Immature birds make "loud chirps and trills".

Status

The IUCN has assessed the coscoroba swan as being of Least Concern. It has a large range and its estimated population of 6,700 to 17,000 mature individuals is believed to be stable. No immediate threats have been identified. The species' population varies dramatically at different parts of its range, being fairly common in Argentina, uncommon in Paraguay and Uruguay, rare in Chile, and uncertain in Brazil. The "[g]reatest threat seems to be loss of temperate marsh habitats due to urbanization and agricultural developments".