Black Swan

The Black Swan (Cygnus atratus) is a large waterbird which breeds mainly in the southeast and southwest regions of Australia.

Contents 1 Taxonomy 2 Description 3 Distribution 3.1 Australia 3.2 Introduced populations 4 Behaviour 4.1 Bearing 4.2 Nesting and reproduction 5 Conservation 6 Australian culture 7 Various views and plumages 8 References 9 External links

Taxonomy

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

The Black Swan was described scientifically by English naturalist John Latham in 1790. It was formerly placed into a monotypic genus, Chenopis.

The common name 'swan' is a gender neutral term, but 'cob' for a male and 'pen' for a female are also used, as is 'cygnet' for the young.^[2] Collective nouns include a 'bank' (on the ground) and a 'wedge' (in flight).^[3] Black Swans can be found singly, or in loose companies numbering into the hundreds or even thousands.^[4]

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.^[4]

A mature Black Swan measures between 110 and 142 cm (43-56 in) in length and weighs 3.7–9 kg (8.1-20 lbs). Its wing span is between 1.6 and 2 metres (5.3-6.5 ft).^[4][5] 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.^[4][6]

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.^[7]

Distribution

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.^[1]

Australia

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.^[4][8] 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.^[4]

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 immigration 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.^[9]

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.^[9]

Introduced populations

Before the arrival of the Māori 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.^[6] 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.^[10]

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,^[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 2003/04 (though that is undoubtedly an under-estimate given the level of monitoring undertaken).

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.^[12]

Behaviour

Bearing

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.^[4]

Nesting and reproduction

Generally, Black Swans nest in the wetter winter months (February to September), occasionally in large colonies. A typical clutch contains 4 to 8 greenish-white eggs that are incubated for about 35–40 days.^[13] After hatching, the cygnets are tended by the parents for about 6 months until fledging, and may ride on their parent's back for longer trips into deeper water.^[4][6][14]

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.^[4][9] A nest is reused every year, restored or rebuilt as needed. Both parents share the care of the nest. Like other swans, the Black Swan is largely monogamous, pairing for life (about 6% divorce rate).^[15] Recent studies have shown that around a third of all broods exhibit extra-pair paternity.^[16] 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.^[17][18]

Conservation

The Black Swan is protected under the Australian National Parks and Wildlife Act, 1974. 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.

Various views and plumages

Head profile

Earliest known illustration, c. 1788–1792

Adult swan drinking

Adult displaying wings, Lake Monger

References

External links

• Birdway - Photos of Black Swans in the wild
• Video, Pictures and Information on the Black Swan
• Black Swan videos, photos & sounds on the Internet Bird Collection