Identification
Chez les adultes, le bec est grand, rouge-orange, avec une barre blanche à son extrémité. Le plumage est entièrement noir. Les plumes du dos sont retroussées et le bout des ailes blanc est surtout visible en vol. Les juvéniles sont semblables aux adultes mais leur plumage est plus terne et plus nuancé de brun. Les plumes des flancs et du dessus sont teintées de brun grisâtre. Les primaires ont une pointe noirâtre. Le plumage adulte peut être acquis dès la fin de la première année mais la bosse frontale rouge ne se forme qu'au bout de la troisième, voire de la quatrième année.

Chant
Le cygne noir drense, drensite, siffle, trompette. Le cri typique est claironnant, aigu, assez mélodieux mais pas très sonore. Il est émis aussi bien sur l'eau qu'en vol. Quand ils sont sur l'eau les cygnes noirs ont également un répertoire de cris plus faibles.

Habitat
Le cygne noir est un oiseau répandu, capable de vivre dans presque tous les milieux humides. Lors de la saison de nidification, on le trouve surtout sur les grands lacs peu profonds, ou à proximité. Le reste de l'année, il fréquente aussi de petits étangs stagnants isolés, les "billabongs", des baies abritées ou des lagunes côtières saumâtres. Le cygne noir est nomade et doté d'un vol puissant. Il peut aisément survoler les terres et sait faire étape sur les lacs ou les zones de culture inondées. Toutefois, là où la nourriture et les sites de nidification sont abondants, le cygne noir se montre casanier. Comptant parmi les oiseaux aquatiques pourvus des meilleurs capacités d'adaptation, le cygne noir recherche d'ordinaire des plans d'eau peu profonds où sa morphologie lui permet de se nourrir commodément.

Comportements
Les cygnes noirs sont grégaires sauf à la période de reproduction où ils défendent leur territoire en faisant preuve d'une grande agressivité. Il arrive cependant que, sans constituer pour autant une colonie, les nids soient situés à faible distance les uns des autres. A ce moment de l'année, les mâles sont particulièrement virulents et chassent les anatidés et presque tous les autres intrus des environs du nid. Malgré cela, ils n'adoptent pas la posture de menace, ailes arquées, que prennent typiquement les cygnes tuberculés. Pour la mue post-nuptiale, les cygnes noirs forment d'énormes rassemblements qui peuvent compter plusieurs milliers d'oiseaux. En mars et en avril, on assiste à des mouvements de dispersion vers le nord, mais ces derniers ne sont pas bien connus. Les cygnes noirs viennent rarement à terre car la brièveté de leurs pattes et la longueur de leur corps constituent un handicap et leur donne une allure peu élégante. Les cygnes noirs décollent et atterrissent moins que les autres cygnes car leurs courtes pattes ne leur permettent pas de s'élancer et de prendre de l'élan.

Nidification
La période de reproduction du cygne noir correspond en général avec la saison des pluies. Ainsi, dans le Queensland, au nord-ouest, il peut nicher dès février ; en Australie Occidentale les œufs ne sont pas pondus avant août. En cas de sècheresse prolongée, le cygne noir ne niche pas du tout. L'espèce construit un gros nid d'ordinaire sur la terre ferme mais toujours près de l'eau. Parfois le nid est installé dans les marais ou même sur un radeau de débris végétaux. Contrairement aux autres cygnes, le cygne noir est étonnamment tolérant à l'égard de ses congénères. Sur des petites îles, il peut exister des colonies de nidifcation où les nids se touchent presque. Le premier œuf vert pâle est pondu dès le début de l'édification du nid, puis 4 ou 5 autres viennent peu après. Les deux adultes se relaient pour couver durant six semaines. L'incubation ne commence qu'une fois la ponte complète ou presque, et les petits cygnes éclosent ainsi tous en deux ou trois jours. Dès l'éclosion, les premiers poussins quittent le nid et gagnent l'eau sous la surveillance d'un adulte. Le second adulte attend l'éclosion des autres œufs puis la famille se réunit au complet.

Régime
Le cygne noir ne se nourrit que de végétaux et ne capture insectes et autres invertébrés que par hasard. Il mange surtout en nageant en immergeant la tête et le cou pour atteindre les plantes sous la surface. En eau plus profonde, le cygne noir peut aussi basculer le corps, queue pointée en l'air et le cou étendu au maximum pour augmenter ses possibilités. Toutes sortes de végétaux sont consommés dont les lentilles d'eau et des algues. Sur les rives des lacs, le cygne noir patauge en mordillant les plantes s'offrant à portée de son long cou et de son bec puissant rouge. On voit souvent le cygne noir pâturant à l'intérieur des terres, loin de l'eau, poussé par son goût pour les céréales cultivées

Protection / Menaces
Avant l'arrivée des européens, le cygne noir était répandu et commun dans toute l'Australie. Les colons le chassant pour sa chair, ses effectifs méridionaux s'effondrèrent. Ce grand oiseau noir était une cible facile, surtout pendant la mue qui lui interdit le vol. Les populations des zones à l'écart continuèrent à prospérer, de même que celles introduites en Nouvelle-Zélande. Grâce à cela, une fois sa protection décidée, le cygne noir a pu rapidement reconstituer ses effectifs et a regagné la plupart du terrain perdu. Dans certaines provinces, la croissance est telle qu'une limitation est appliquée pour lutter contre les dégâts causés aux cultures par les grandes troupes.

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The Black Swan (Cygnus atratus) is a large waterbird, a species of swan, which breeds mainly in the southeast and southwest regions of Australia. The species was hunted to extinction in New Zealand, but later reintroduced. 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 that share incubation duties and cygnet rearing between the sexes. 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
Black Swans are primarily 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 (8.2–20 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. 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.

Distribution
The Black Swan is common in the wetlands of south western and eastern Australia and adjacent coastal islands. In the south west the range ecompasses an area between North West Cape, Cape Leeuwin and Eucla; while in the east it covers are 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 (This time may vary). During this time they will usually settle on large, open waters for safety. The species has a large range, with figures between one to 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
Before the arrival of the Maori in New Zealand, a subspecies of the Black Swan known as the New Zealand Swan had developed in the islands, 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 and 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. The Black Swan is also very popular as an ornamental waterbird in western Europe, especially Britain, and escapes 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, 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 2003/04.
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.

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 like Vallisneria. In Queensland aquatic plants like Potamogeton and 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 bird up-ends to reach lower. Black Swans are also able to filter feed at the water's surface.

Nesting and reproduction
Generally, Black Swans 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, in order 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
The Black Swan is protected under the Australian National Parks and Wildlife Act, 1979. It is evaluated as Least Concern on the IUCN Red List of Threatened Species.

Australian culture
The Black Swan was a literary or artistic image, even before the discovery of Cygnus atratus. 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 and bird emblem, of Western Australia; it also appears in the Coat of Arms and other iconography of the state's institutions.