Coscoroba

The coscoroba swan (''Coscoroba coscoroba'') is a species of waterfowl in the subfamily Anserinae of the family Anatidae.HBW and BirdLife International (2021) Handbook of the Birds of the World and BirdLife International digital checklist of the birds of the world. Version 6. Available at: http://datazone.birdlife.org/userfiles/file/Species/Taxonomy/HBW-BirdLife_Checklist_v6_Dec21.zip retrieved August 7, 2022 It is found in Argentina, Bolivia, Brazil, Chile, Paraguay, Uruguay, and the Falkland Islands.Remsen, J. V., Jr., J. I. Areta, E. Bonaccorso, S. Claramunt, A. Jaramillo, D. F. Lane, J. F. Pacheco, M. B. Robbins, F. G. Stiles, and K. J. Zimmer. Version 24 July 2022. Species Lists of Birds for South American Countries and Territories. https://www.museum.lsu.edu/~Remsen/SACCCountryLists.htm retrieved July 24, 2022

Taxonomy and systematics

The coscoroba swan's placement within the family Anatidae is not fully agreed upon, with a 2014 genetic study positing a phylogenetic relationship between this species and the Cape Barren goose (''Cereopsis novaehollandiae''). BirdLife International's ''Handbook of the Birds of the World'' has adopted this approach and places the coscoroba swan and Cape Barren goose together in the tribe Cereopsini, which it places as basal to ''Cygnus'' and all other geese. However, the South American Classification Committee of the American Ornithological Society, the International Ornithological Committee (IOC), and the Clements taxonomy treat the Cape Barren goose as basal to other geese, which themselves precede the coscoroba and other swans in a linear sequence. Even those three systems differ, with the IOC placing the coscoroba before ''Cygnus'' and the other two after it in their lists.Remsen, J. V., Jr., J. I. Areta, E. Bonaccorso, S. Claramunt, A. Jaramillo, D. F. Lane, J. F. Pacheco, M. B. Robbins, F. G. Stiles, and K. J. Zimmer. Version 24 July 2022. A classification of the bird species of South America. American Ornithological Society. https://www.museum.lsu.edu/~Remsen/SACCBaseline.htm retrieved July 24, 2022Clements, J. F., T. S. Schulenberg, M. J. Iliff, S. M. Billerman, T. A. Fredericks, J. A. Gerbracht, D. Lepage, B. L. Sullivan, and C. L. Wood. 2021. The eBird/Clements checklist of Birds of the World: v2021. Downloaded from https://www.birds.cornell.edu/clementschecklist/download/ Retrieved August 25, 2021

The coscoroba swan is the only member of the genus ''Coscoroba'' and has no subspecies.

Description

The coscoroba swan is a medium-large sized waterfowl, but smaller than the true swans, at long with a wingspan of about . Males weigh and females . Their appearance is considered to be slightly unusual, being intermediate between that of geese and true swans. They have completely feathered faces—unusual for true swans—and their feet are located directly under their bodies, enabling the coscoroba swan to walk more efficiently than the “waddling” of most waterfowl. Physically, coscoroba swans have been compared to the American Pekin duck, albeit larger and with darker, redder bills and feet (Pekin ducks have bright orange bills and feet). The sexes have the same plumage; upon hatching, the chicks have blue-grey bills and feet and black striping running down the length of their bodies (to aid in camouflage from predators), with this eventually fading by about eight months of age. The adults are completely white, except for black tips to the outer six primary feathers, though this black is often barely visible on the closed wing unless the bird is in flight.

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 and at least one at .

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 seldom 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 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 with dimensions of about . Males guard females during the incubation period of about 35 days. Both parents care for the young through fledging at 14 weeks and beyond, sometimes until they are a year old. 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 6700 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 " eatest threat seems to be loss of temperate marsh habitats due to urbanization and agricultural developments".

Gallery

File:Coscoroba coscoroba -Mostardas, Rio Grande do Sul, Brasil -juvenile-8.jpg, Juveniles in Rio Grande do Sul, Brazil
File:Coscoroba coscoroba (Coscoroba Swan - Koskorobaschwan) - Weltvogelpark 2012-01.jpg, Bath taking at Weltvogelpark Walsrode
File:Coscoroba.swan.2.arp.750pix.jpg, Swimming
File:Coscoroba Swan - Berlin Zoo.jpg, At Berlin Zoo, Germany

References

{{Taxonbar, from=Q144218

Swans
Anserinae
Birds of Argentina
Birds of the Falkland Islands
Birds described in 1782