Cisne Negro/Black Swan/Cygnus atratus

Foto: Ramiro Ramirez

Nombre en español: Cisne Negro

Nombre en inglés: Black Swan

Nombre científico: Cygnus atratus

Familia: Anatidae

Canto: Stanislas Wroza

El cisne negro (Cygnus atratus) es una especie de ave anseriforme de la familia Anatidae endémica de Australia. Fue descubierto en 1697, a principios del siglo XVIII, los colonos ingleses que volvieron de Australia trajeron consigo, en sus barcos, un cargamento. Los cisnes negros son propios de Australia y hasta ese momento, se pensaba que todos los cisnes eran blancos, porque de ese color eran todos los cisnes que se conocían hasta entonces. La intrahistoria de esta historia es que este hecho supuso una conmoción en la sociedad inglesa. Aunque nos pueda parecer algo ingenuo lo cierto es que la aparición de una especie de cisnes de un color distinto al que estaban acostumbrados a ver, supuso para los habitantes de la época una fuente de debate y de polémica. Ha sido el favorito de los estanques ornamentales de Europa, y posteriormente de América, pero no se ha asilvestrado en estos continentes.

Características

No hay dimorfismo sexual en el plumaje de los individuos. Los machos son más grandes que las hembras; tienen una longitud total de 1,2 a 1,4 m una envergadura alar de 1,6 a 2 m, y un peso de 6,3 kg a 8,7 kg. Las hembras tienen un peso medio de 5,1 kg. Los juveniles tienen el plumaje blanco, realmente plumón, hasta aproximadamente los 6 meses que les salen las plumas negras. El pico es rojo.

Distribución

Es común al este y oeste de Australia, no estando presente la parte árida central y del húmeda del norte. Es residente en Tasmania, criando en esta isla. Fue introducido en Nueva Zelanda, donde se reprodujo de tal forma, que hubo que controlarlo. Actualmente se estima que existen entre 300.000 y 500.000 individuos.

Hábitat

Vive en lagos, aunque puede observarse con cierta frecuencia en costas marinas y ocasionalmente en mar abierto. Demuestra preferencia por los lagos pocos profundos, donde puede alcanzar la vegetación acuática del fondo, sumergiendo su cuello, aproximadamente a un metro de profundidad.Cygnus atratus – MHNT

Reproducción

Nidifica en la temporada de lluvia. Anida en colonias compuestas por pocas hasta miles de parejas, con los nidos cerca uno de otros. El nido lo construye en pequeñas islas o islotes, sobre vegetación acuática. El nido es una plataforma de hierbas y puede medir dos metros de diámetro por un metro de alto.

Generalmente pone de 3 a 7 huevos color verde pálido; pudiendo haber, raras veces, puestas de 1 ó 2 o incluso hasta 10 huevos. La incubación toma entre 35 a 45 días. Los polluelos nacen con plumaje blanco, se suben sobre las espaldas de los padres de pequeños. A los 6 meses recién pueden volar. A los dos años ya son adultos.

Comportamiento

El cisne negro es bastante sociable. Pasada la temporada de cría se reúnen formando grandes grupos. En Nueva Zelanda, en el lago Ellesmere, se han estimado concentraciones hasta de 70.000 individuos. No es migratorio, pero se desplaza a grandes distancias, cientos de kilómetros, en busca de abundancia de alimento.

Dieta y alimentación

El cisne negro es casi exclusivamente herbívoro, y si bien hay algunas variaciones regionales y de temporada, la dieta generalmente está dominada por plantas acuáticas y de pantano. En Nueva Gales del Sur, la hoja espadaña (género Typha) es el alimento más importante de las aves en los humedales, seguido de las algas y plantas acuáticas sumergidas, como Vallisneria. En Queensland las plantas acuáticas como el Potamogeton, stoneworts y demás algas son alimentos dominantes. La composición exacta varía con el nivel del agua; en caso de inundaciones donde los alimentos normales están fuera del alcance de los cisnes negros, se alimentan de pasto en tierra. El Cisne Negro toma los alimentos de una manera similar a otros cisnes. Cuando se alimenta en aguas poco profundas se moja la cabeza y el cuello bajo el agua, y es capaz de mantener su cabeza plana contra la parte inferior mientras se mantiene su cuerpo flotando horizontalmente. En aguas más profundas el ave puede llegar más bajo. Los cisnes negros también son capaces de filtrar la comida en la superficie del agua.

Anidación y reproducción

Al igual que otros cisnes, el cisne negro es principalmente monógamo,​ con una vinculación de por vida (alrededor del 6% se separan). Los estudios recientes han demostrado que alrededor de un tercio de todas las crías no pertenecen a la pareja de paternidad. Se estima que una cuarta parte de todas las parejas son Homosexuales,​ sobre todo entre los varones. Ellos roban los nidos, o forman tríos temporales con hembras para obtener huevos, ahuyentando a la hembra después de que ella pone los huevos.

En general, los cisnes anidan en los meses de invierno más húmedos (de febrero a septiembre), a veces en grandes colonias. Un nido de cisne negro es esencialmente un montón grande o montículo de cañas, pastos y malezas de entre 1 0 1,5 metros (3-4 ½ pies) de diámetro y de hasta 1 metro de altura, en aguas poco profundas o en las islas. El nido se vuelve a utilizar todos los años, restaurados o reconstruidos, según sea necesario. Los padres comparten el cuidado del nido. Los huevos son de color blanco verdoso y la hembra tiende a poner de 4 a 8 huevos que son incubados durante unos 35-40 días.​ La incubación comienza después de la colocación del último huevo, con el fin de sincronizar la eclosión de los polluelos. Antes del comienzo de la incubación los padres se sientan sobre los huevos sin llegar a calentarlos. Ambos sexos incuban la puesta, aunque las hembras suelen incubar por la noche. Si los huevos accidentalmente caen fuera del nido, ambos sexos van a recuperar el huevo con el cuello (en otras especies sólo la hembra lleva a cabo esta hazaña). Al igual que todos los cisnes, defienden agresivamente los nidos con sus alas y picos. Después de la eclosión, los polluelos son cuidados por los padres durante unos 9 meses. Los cigoñinos pueden montar a lomo de sus padres para realizar viajes más largos o en aguas más profundas, pero este comportamiento es menos frecuente que en el cisne común (Cygnus olor) y el de cuello negro (Cygnus melancoryphus).

Foto: Ramiro Ramirez

Black swan

The black swan (Cygnus atratus) is a large waterbird, a species of swan which breeds mainly in the southeast and southwest regions of Australia. Within Australia they are nomadic, with erratic migration patterns dependent upon climatic conditions. Black swans are large birds with mostly black plumage and red bills. They are monogamous breeders, with both partners sharing incubation and cygnet rearing duties.

Black swans were introduced to various countries as an ornamental bird in the 1800s, but have escaped and formed stable populations. A small population of black swans exists on the River Thames at Marlow, on the Brook running through the small town of Dawlish in Devon (they have become the symbol of the town), near the River Itchen, Hampshire, and the River Tees near Stockton on Tees. Described scientifically by English naturalist John Latham in 1790, the black swan was formerly placed into a monotypic genus, Chenopis. Black swans can be found singly, or in loose companies numbering into the hundreds or even thousands. Black swans are popular birds in zoological gardens and bird collections, and escapees are sometimes seen outside their natural range.

Description

Side view of mature adult showing characteristic «S» neckNear Devonport, Tasmania with wings raised in an aggressive display revealing white flight feathers

Black swans are mostly black-feathered birds, with white flight feathers. The bill is bright red, with a pale bar and tip; and legs and feet are greyish-black. Cobs (males) are slightly larger than pens (females), with a longer and straighter bill. Cygnets (immature birds) are a greyish-brown with pale-edged feathers.

A mature black swan measures between 110 and 142 centimetres (43 and 56 in) in length and weighs 3.7–9 kilograms (8.2–19.8 lb). Its wing span is between 1.6 and 2 metres (5.2 and 6.6 ft). The neck is long (relatively the longest neck among the swans) and curved in an «S»-shape.

The black swan utters a musical and far reaching bugle-like sound, called either on the water or in flight, as well as a range of softer crooning notes. It can also whistle, especially when disturbed while breeding and nesting.

When swimming, black swans hold their necks arched or erect and often carry their feathers or wings raised in an aggressive display. In flight, a wedge of black swans will form as a line or a V, with the individual birds flying strongly with undulating long necks, making whistling sounds with their wings and baying, bugling or trumpeting calls. Black swan skeleton (Museum of Osteology)

The black swan is unlike any other Australian bird, although in poor light and at long range it may be confused with a magpie goose in flight. However, the black swan can be distinguished by its much longer neck and slower wing beat.

One captive population of black swans in Lakeland, Florida has produced a few individuals which are a light mottled grey colour instead of black.

Distribution

The black swan is common in the wetlands of southwestern and eastern Australia and adjacent coastal islands. In the south west the range encompasses an area between North West Cape, Cape Leeuwin and Eucla; while in the east it covers a large region bounded by the Atherton Tableland, the Eyre Peninsula and Tasmania, with the Murray Darling Basin supporting very large populations of black swans. It is uncommon in central and northern Australia.

The black swan’s preferred habitat extends across fresh, brackish and salt water lakes, swamps and rivers with underwater and emergent vegetation for food and nesting materials. Permanent wetlands are preferred, including ornamental lakes, but black swans can also be found in flooded pastures and tidal mudflats, and occasionally on the open sea near islands or the shore.

Black swans were once thought to be sedentary, but the species is now known to be highly nomadic. There is no set migratory pattern, but rather opportunistic responses to either rainfall or drought. In high rainfall years, emigration occurs from the south west and south east into the interior, with a reverse migration to these heartlands in drier years. When rain does fall in the arid central regions, black swans will migrate to these areas to nest and raise their young. However, should dry conditions return before the young have been raised, the adult birds will abandon the nests and their eggs or cygnets and return to wetter areas.

Black swans, like many other water fowl, lose all their flight feathers at once when they moult after breeding and they are unable to fly for about a month. During this time they will usually settle on large, open waters for safety.

The species has a large range, with figures between one and ten million km2 given as the extent of occurrence. The current global population is estimated to be up to 500,000 individuals. No threat of extinction or significant decline in population has been identified with this numerous and widespread bird.

Black swans were first seen by Europeans in 1697, when Willem de Vlamingh’s expedition explored the Swan River, Western Australia.

Introduced populations

New Zealand

Before the arrival of the Māori in New Zealand, a related species of swan known as the New Zealand swan had developed there, but was apparently hunted to extinction. In 1864, the Australian black swan was introduced to New Zealand as an ornamental waterfowl and populations are now common on larger coastal or inland lakes, especially Rotorua Lakes, Lake Wairarapa, Lake Ellesmere, and the Chatham Islands. Black swans have also naturally flown to New Zealand, leading scientists to consider them a native rather than exotic species, although the present population appears to be largely descended from deliberate introductions.

United Kingdom

The black swan is also very popular as an ornamental waterbird in western Europe, especially Britain, and escapees are commonly reported. As yet, the population in Britain is not considered to be self-sustaining and so the species is not afforded admission to the official British List,[11] but the Wildfowl and Wetlands Trust have recorded a maximum of nine breeding pairs in the UK in 2001, with an estimate of 43 feral birds in 2003–2004. A colony of black swans in Dawlish, Devon has become so well associated with the town that the bird has been the town’s emblem for forty years.

Japan

There are also wild populations in Japan, having originally been imported during 1950–1960.

United States

Black swans have been reported in Florida, USA, but there is no evidence that these examples are breeding; persistent sightings may be due to continuing releases or escapes. In addition, black swans used to live in Lake Junaluska, a large lake in Waynesville, North Carolina.

China

Black swans can also be found in China. In 2018 one group of swans was introduced to the Shenzhen University campus on an artificial lake in Guangdong Province.

Behaviour

Up-ending in deeper water to reach foodCygnus atratus, spring rain

Diet and feeding

The black swan is almost exclusively herbivorous, and while there is some regional and seasonal variation, the diet is generally dominated by aquatic and marshland plants. In New South Wales the leaf of reedmace (genus Typha) is the most important food of birds in wetlands, followed by submerged algae and aquatic plants such as Vallisneria. In Queensland, aquatic plants such as Potamogeton, stoneworts, and algae are the dominant foods. The exact composition varies with water level; in flood situations where normal foods are out of reach black swans will feed on pasture plants on shore. The black swan feeds in a similar manner to other swans. When feeding in shallow water it will dip its head and neck under the water and it is able to keep its head flat against the bottom while keeping its body horizontal. In deeper water the swan up-ends to reach lower. Black swans are also able to filter feed at the water’s surface.

Nesting and reproduction

Like other swans, the black swan is largely monogamous, pairing for life (about 6% divorce rate). Recent studies have shown that around a third of all broods exhibit extra-pair paternity. An estimated one-quarter of all pairings are homosexual, mostly between males. They steal nests, or form temporary threesomes with females to obtain eggs, driving away the female after she lays the eggs.

Generally, black swans in the Southern hemisphere nest in the wetter winter months (February to September), occasionally in large colonies. A black swan nest is essentially a large heap or mound of reeds, grasses and weeds between 1 and 1.5 metres (3–4½ feet) in diameter and up to 1 metre high, in shallow water or on islands. A nest is reused every year, restored or rebuilt as needed. Both parents share the care of the nest. A typical clutch contains 4 to 8 greenish-white eggs that are incubated for about 35–40 days. Incubation begins after the laying of the last egg, to synchronise the hatching of the chicks. Prior to the commencement of incubation the parent will sit over the eggs without actually warming them. Both sexes incubate the eggs, with the female incubating at night. The change over between incubation periods is marked by ritualised displays by both sexes. If eggs accidentally roll out of the nest both sexes will retrieve the egg using the neck (in other swan species only the female performs this feat). Like all swans, black swans will aggressively defend their nests with their wings and beaks. After hatching, the cygnets are tended by the parents for about 9 months until fledging. Cygnets may ride on their parent’s back for longer trips into deeper water, but black swans undertake this behaviour less frequently than mute and black-necked swans.

Relationship with humans

Willem de Vlamingh’s ships, with black swans, at the entrance to the Swan River, Western Australia (1696–1697)

Conservation

The black swan is protected in New South Wales, Australia under the National Parks and Wildlife Act 1974 (s.5). It is evaluated as Least Concern on the IUCN Red List of Threatened Species.

Australian culture

The state flag of Western Australia was officially adopted in 1870 and modified slightly in 1953.Main article: Black swan emblems and popular culture

The black swan was a literary or artistic image among Europeans even before their settlement of Australia. Cultural reference has been based on symbolic contrast and as a distinctive motif.

The black swan’s role in Australian heraldry and culture extends to the first founding of the colonies in the eighteenth century. It has often been equated with antipodean identity, the contrast to the white swan of the northern hemisphere indicating ‘Australianness’. The black swan is featured on the flag, and is both the state bird and state emblem of Western Australia; it also appears in the Coat of Arms and other iconography of the state’s institutions.

Indigenous Australia

The Noongar People of the South-West of Australia call the black swan Kooldjak along the West and South-West coast, Gooldjak in the South East and it is sometimes referred to as maali in language schools.

Fuentes: Wikipedia/eBird/xeno-canto

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