Black swan

Name and taxonomy

The English naturalist John Latham described the bird in 1790 as Anas atrata. Later authors moved it into a genus of its own, Chenopis. In 1997 it went into Cygnus, the swan genus, with Chenopis kept as a subgenus. The species is monotypic, so no subspecies are recognised.

Australian languages have their own names for the bird. In Noongar, spoken across the south west, it is kuljak, kooldjak or gooldjak. Language schools sometimes use the name maali. The Teen Toomele Menennye people of Tasmania call it pickerdar.

Evolution and relatives

Swans, geese and ducks share the family Anatidae, and swans are the largest of them. The nearest relative of the black swan is the mute swan of Eurasia. Its neck is the longest of any swan in proportion to the body. The all-black plumage probably developed in isolation on an island continent.

New Zealand once held a swan of its own. People hunted that bird out before Europeans reached the islands. Settlers filled the gap in 1864 with black swans shipped from Australia. A few birds have also crossed the Tasman Sea on their own. The present New Zealand population descends mostly from the deliberate releases.

Appearance

The body feathers are black and the flight feathers are white. A swimming bird therefore appears wholly black until it lifts a wing. A pale bar and a pale tip mark the bright red bill. The legs and feet are greyish black, and the eye is red or pink. The long neck curves into an S when the bird swims.

A male is called a cob and a female a pen. The cob is slightly larger, and his bill is longer and straighter. Wikidata gives adult averages of 6.2 kilograms for males and 5.1 kg for females. Cygnets are greyish brown with pale feather edges and a paler bill. A captive flock in Florida has thrown a few mottled grey birds. White individuals also occur, and they are leucistic rather than albino.

Habitat and range

The stronghold is the wetland country of south-western and eastern Australia. In the west the range lies between North West Cape, Cape Leeuwin and Eucla. In the east it runs from the Atherton Tableland to the Eyre Peninsula and Tasmania. The Murray and Darling basin carries very large numbers. The bird is uncommon in central and northern Australia.

Fresh, brackish and salt water all suit it, if plants grow in and around the water. Lakes, swamps, rivers, flooded pasture and tidal mudflats all serve. Ornamental lakes in parks and gardens suit the species just as well. Birds sometimes turn up on the open sea near a shore or an island. Published figures for the extent of the range run from 1 to 10 million square kilometres. GBIF holds records from 85 countries, and that count includes park birds and escapes.

Diet and feeding

The black swan eats plants almost exclusively. Water plants and marsh plants make up the bulk of the diet. Reedmace leaves are the main item for birds in New South Wales wetlands. Queensland birds take pondweed, stoneworts and algae instead. The mixture shifts with the water level and the season. Insects turn up in the diet now and then.

In shallow water the swan pushes its head and neck under and grazes the bottom. It holds the body level while the head works below. In deeper water it up-ends, tail in the air, to reach further down. It can also strain food from the surface film. When a flood puts the usual plants out of reach, the birds graze pasture on shore. That habit makes them a crop pest in some districts.

Behaviour and social life

Black swans gather in loose companies of hundreds or even thousands of birds. They are the least territorial of the swans, and some pairs nest in colonies. A single bird or a lone pair is just as common a sight. The species is nomadic and follows the rain. Wet years draw birds inland from the south, and dry years send them back. When rain reaches the dry centre, swans fly there to nest.

If the drought returns too soon, the parents leave the eggs or cygnets behind. After breeding the swan drops every flight feather at once. It cannot fly for about a month, so it settles on wide open water for safety. Feeding peaks at dusk, and the birds often travel at night, calling as they go. A threat display raises the neck, points the bill down and ruffles the feathers. The wings then beat two or three loud strokes, followed by a call.

Communication and senses

The main call is a musical bugle that carries a long way. The swan gives it on the water and in the air. Softer crooning notes serve at close range. A bird disturbed at the nest whistles. The wings whistle too, so a passing flock can be heard before it is seen.

The triumph ceremony is the most elaborate display of the species. The male approaches with his wings and chin raised, calling again and again. The female answers with the same call, and the two dip their heads in turn. They stretch their necks upward, point the bills, and then swim in a circle. The ceremony binds mates together and links parents to their cygnets. It grows more frequent when other swans are near.

Reproduction and life cycle

Black swans pair for life, and only about 6 per cent of pairs split up. Around a third of broods contain a chick fathered outside the pair. About a quarter of pairings join two birds of the same sex, usually two males. Such pairs take over a nest, or bring in a female and drive her off after she lays. Breeding runs through the wetter months, from February to September.

The nest is a heap of reeds, grasses and weed in shallow water or on an island. It measures 1 to 1.5 metres across and stands up to a metre high. The same mound serves each year, repaired or rebuilt as needed. A clutch holds four to eight greenish white eggs. An egg is 9.5 to 11.7 cm long and weighs 200 to 320 grams.

Both parents incubate, and the female takes the night shift. Sitting lasts about 35 to 40 days and begins once the last egg is laid. That timing makes the whole brood hatch together. Either parent can roll a stray egg back with the neck. In every other swan only the female performs that trick. Both birds defend the nest fiercely with the wings and the bill.

Cygnets swim and feed soon after they hatch. They ride on a parent's back for a long trip into deep water. Black swans do this less often than mute and black-necked swans. The young fly at about six months and stay with the family for about nine. First breeding comes at 18 to 36 months old. The oldest ringed bird passed 24.7 years, and wild swans of 40 are reported.

Predators and threats

An adult black swan is large, and few predators appear to trouble a healthy one. Eggs are taken by Australian ravens, by common rats and by golden-bellied water rats. Swamp harriers and white-bellied sea eagles rob nests, and so do other hawks. Fledglings fall to harriers, sea eagles, quolls, water rats, gulls and terns. Parents meet an attacker with raised wings and a stabbing bill.

Drought is probably the largest natural threat to the species. A dry season can end a whole round of breeding across the interior. Some districts run a hunting season where flocks damage crops. The bird is fully protected in every Australian state and may not be shot. New South Wales protects it under an act of 1974. The moult leaves adults flightless for a month, which is probably the riskiest time.

Population and conservation

The IUCN lists the black swan as Least Concern. The world population is put at up to 500,000 birds. No decline and no threat of extinction have been identified. New South Wales alone counts numbers in the thousands and tens of thousands. iNaturalist holds 39,028 observations of the species.

Introduced flocks probably add a little to the world total. New Zealand now holds large numbers on its coastal and inland lakes. Rotorua, Lake Wairarapa, Te Waihora and the Chatham Islands all carry them. The British population is not counted as self-sustaining. The Wildfowl and Wetlands Trust logged nine breeding pairs in Britain in 2001. It estimated 43 feral birds there across 2003 and 2004.

Relationship with humans

Europeans first saw the bird in 1697, when Willem de Vlamingh explored the Swan River. The species went abroad as an ornamental bird during the 1800s. Escapes founded stable flocks in several countries. New Zealand received birds in 1864, and Japan between 1950 and 1960. British groups live at Marlow on the Thames, at Dawlish in Devon and near Stockton-on-Tees. A campus flock went onto an artificial lake at Shenzhen University in 2018.

Zoos and park lakes keep the bird, probably because it looks striking and tolerates people. Farmers count it a pest where a flock grazes a crop or pulls it up. People take the eggs in some places. Birdwatchers rate the species highly, and it draws visitors to park lakes. The swan is not domesticated, and captive birds appear to keep their wild behaviour.

In culture and myth

The black swan is the emblem of Western Australia. It stands on the state flag as a black bird on a yellow disc. The design dates from 1870, and the swan became the official state bird in 1973. At first the bird faced away from the hoist, which broke the rules of flag design. The direction was reversed in 1953, ahead of a royal visit. Western Australia used one postage stamp from 1854 to 1902, and it carried the swan.

The Roman poet Juvenal wrote of a rare bird that was very like a black swan. For Europeans the phrase named a thing that could not exist. The sighting of 1697 turned it into a figure for the unforeseen instead. Nassim Nicholas Taleb built a theory of rare events on the phrase from 2001. His three tests are surprise, extreme effect, and an explanation invented afterwards.

The town of Dawlish in Devon has used the introduced bird as its emblem for forty years. Australians have long read the swan as a mark of their own half of the world. The white swan of the northern hemisphere stands opposite it. The bird appears in the coat of arms and the badges of Western Australian institutions.