Black Swan
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 110-142 centimetresin length and weighs 3.7–9 kilograms. Its wing span is between 1.6-2 metres. The neck is long and curved in an "S"shape.
Habitat
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.
Diet
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 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.
Breeding
Like other swans, the black swan is largely monogamous, pairing for life. 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 (Feb-Sep), occasionally in large colonies. A black swan nest is essentially a large heap or mound of reeds, grasses and weeds in shallow waters 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 4-8 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 swans and black-necked swans.
Population
According to the IUCN Red List they are classed as least concern and the population trend is stable. They were lasted assesed on th 9th August 2018. The global population is estimated to number 100,000-1,000,000 individuals, while the population in Japan has been estimated at 100-10,000 introduced breeding pairs. The population is suspected to remain stable in the absence of evidence for any declines or substantial threats.