Mute swan

Name and taxonomy

Johann Friedrich Gmelin named the bird Anas olor in 1789. Johann Matthaus Bechstein moved it into the new genus Cygnus in 1803. Both parts of the modern name mean swan in Latin. Cygnus is a variant of cycnus, which came from the Greek kyknos. English calls the male a cob, the female a pen and the young a cygnet.

The species is monotypic, so there are no living subspecies. One colour morph is named the Polish swan and carries a gene for leucism. Polish swans have pink legs rather than dark grey ones, and their cygnets hatch dull white. The morph turns up only where the birds have a history of being kept, so domestication seems to explain it.

Evolution and relatives

The mute swan belongs to Anatidae, the family of ducks, geese and swans. Its closest living relatives are not the northern swans it lives beside. Genetic work puts Australia's black swan nearest to it, along with the black-necked swan of South America. That result suggests the group spread widely and then split by hemisphere.

Subfossil bones about 6,000 years old have come out of peat beds in East Anglia. Older material dates a French record to 13,000 years before the present. A fossil subspecies from Azerbaijan differed from the living bird only in size. A giant flightless relative, Cygnus falconeri, lived on Malta and Sicily in the Middle Pleistocene. Swan fossils from California, Arizona, Idaho and Oregon run from the Miocene to about 10,000 years ago.

Appearance

The adult is white all over, with dark grey legs and feet. Head and neck feathers often stain orange-brown, because iron and tannins in the water soak into them. The bill is orange, with black at the nostrils and a black nail at the tip. Adults measure 140 to 160 cm, and extreme birds run from 125 to 170 cm. The wingspan reaches 200 to 240 cm.

This is one of the heaviest birds that can still leave the ground. Males in British studies averaged about 10.6 to 11.87 kg, with a spread of 9.2 to 14.3 kg. Females averaged about 8.5 to 9.67 kg and ranged from 7.6 to 10.6 kg. About 15 kg is the top normal weight for a big male. One Polish male weighed almost 23 kg, and no heavier flying bird has been confirmed.

Cygnets look nothing like their parents in the first year. Their down runs from grey to buff, and their bills are a dull greyish black. They reach close to adult size about three months after hatching. Grey feathers stay until the bird is at least a year old. A swimming mute swan curves its neck and points the bill down, which no other northern swan does.

Habitat and range

Mute swans use fresh water of medium to large size. Lagoons, lakes and slow rivers all hold them. In winter more birds move onto sheltered salt water and open bays. Ground near water serves the birds outside the breeding season, because they graze on land as well. Town parks and city rivers appear to suit the species as well as any wild lake.

The native range covers temperate Europe and the Palearctic east to Primorsky Krai. Winter takes some birds south to North Africa, the Near East, northwest India and Korea. Birds in Britain, Ireland and northwest Europe mostly stay put all year. Birds from Mongolia, eastern Russia and China fly thousands of kilometres to the lower Yellow River. That journey takes 30 to 32 days.

North America holds the largest population outside the native range. The birds arrived there in the late nineteenth century and spread from park collections. Smaller introduced groups live in Australasia and southern Africa. Japan has about 200 birds and South Africa about 120. A feral flock near Northam in Western Australia numbered 80 in the 1980s and about 10 by 2015.

Diet and feeding

The mute swan eats water plants above all else. It does not dive, and it pushes its head and long neck under instead. That reach lets it feed in deeper water than ducks can work. Ducks and gulls often sit near a feeding swan and take the weed that floats up. Small amounts of aquatic insects, fish and frogs go down with the plants.

The birds also graze on dry land. Oilseed rape and wheat both appear in the diet where farms run to the water. A winter flock can do real damage to a crop. Much of that loss comes from trampling with the large webbed feet rather than from eating. Heavy grazing also thins the submerged plants of a lake, which is the core of the North American complaint.

Behaviour and social life

A breeding pair holds a territory and drives other swans off it. One pair may take a whole small lake, and territories run from 4 to 10 acres. Where food is very rich the birds nest close together instead. The largest colonies pass 100 pairs, and Abbotsbury in Dorset is the best known. Nests in such places can sit as little as 2 metres apart.

Young birds that have not paired gather into flocks. These flocks can hold several hundred birds and return to the same sites each year. A count on the Tweed estuary at Berwick reached 787 birds. Birds join these flocks at about three or four years old and leave them when they pair.

Busking is the threat display of this species. The bird arches its neck back, half raises its wings and paddles with both feet at once. The same posture catches the wind, and swans use it to sail several hundred metres. Birders call that trick windsurfing. Swans are also known to mourn a lost mate, and a widowed bird may stay or join a flock.

Communication and senses

The mute swan has sharp sight and good hearing. It is quieter than other northern swans, because its windpipe runs straight instead of looping. The usual sounds are grunts, snorts, hoarse whistles and short barking notes. A hiss is the standard warning to any rival or intruder.

The loudest signal appears to be no call at all. The wings throb in flight with a sound unique to this species. That throb carries 1 to 2 km and probably keeps flying birds in contact. Cygnets whistle and chirp when content and give harsher chirps when lost.

Courting birds perform a rhythmic song that matches the movement of their heads and necks. In an established pair the rhythm and the movement fit together. In a new pair they do not, so the display appears to show how long two birds have been together. Much of the rest of the signalling is posture, and an angry male arches his wing feathers over his back.

Reproduction and life cycle

Mute swans form monogamous pairs, but not always for life. Some birds have taken four mates over their lives, and some leave one partner for another. Established pairs raise more young than newly formed ones. Breeding starts in March or early April, and first breeding comes at about three years old.

The nest is a large mound of waterside plants, lined with down and feathers. The birds build it in shallow water, on an island or at the lake edge. Pairs often use the same mound year after year and repair it each spring. A clutch usually holds 5 to 8 eggs, and both latitude and season affect the number. Each egg weighs 294 to 396 grams, and one exceptional egg passed 500 g.

The female does most of the sitting while the male stands guard. Incubation lasts about 36 days, and cygnets normally hatch between May and July. A cygnet hatches at 180 to 248 g and leaves the nest after about a day. Tired cygnets climb onto a parent's back on the water, and they shelter under a wing in heavy rain.

The young can fly 60 to 65 days after hatching. They fledge properly after 120 to 150 days, at 70 to 75 percent of adult mass. Parents drive them off before the next breeding season. The oldest ringed wild bird on record lived to 26.8 years. Captive swans reach 30 to 40 years.

Predators and threats

A healthy adult swan is rarely killed by a wild predator. Wild boar and hooded crows take eggs in the native range. Red foxes, northern pike and American mink take cygnets. Snapping turtles are the main cygnet predator in New York state. Golden eagles have killed adult swans in a few recorded cases.

Human activity kills far more swans than wild predators do. Power lines and lead poisoning are the two large causes. British numbers fell from about 1960 to the early 1980s, as birds swallowed lead shot and fishing weights. Numbers rose again once lead weights and shot were replaced. Loose dogs now attack swans in British parks, which is a criminal offence there.

Population and conservation

Counted after breeding, with the young included, the native population comes to about 500,000 birds. Up to 350,000 of those are in Russia, and 11,000 pairs breed in the Volga Delta alone. Britain held about 22,000 birds in the winter of 2006 to 2007, including about 5,300 breeding pairs. Germany holds 6,800 to 8,300 pairs, Denmark 4,500 and Poland 4,000 to 4,200. Naturalists have logged 185811 records of the species on iNaturalist.

Hunting almost cleared western Europe of mute swans between the thirteenth and nineteenth centuries. Only the semi-domestic birds of large estates came through. Protection from the late nineteenth century let the species take back most of its old range. GBIF holds records from 99 countries and territories.

North America appears to run the opposite policy. Numbers in the lower Great Lakes grew by at least 10 percent a year from 1971 to 2000. The US Fish and Wildlife Service proposed a 67 percent cut in the Atlantic Flyway in 2003. The Department of the Interior declared the bird non-native and unprotected in 2005. New Zealand lowered its protection in 2010, so the bird may now be killed at the minister's discretion.

Relationship with humans

Britain kept mute swans as poultry for centuries. Owners cut nicks into the webs or the bill of a bird to mark it, and registered the marks with the Crown. Any unmarked bird belonged to the Crown, which is the root of the phrase royal bird. That system of ownership saved the species from being hunted out of Britain. Feathers went into quill pens, the webs into purses and the wing bones into whistles.

The monarch still owns every unmarked mute swan on open water. King Charles III exercises the right only on parts of the Thames and its tributaries. The Vintners' and Dyers' Companies have shared that ownership since the fifteenth century. Swan upping counts and rings the Thames birds each July over five days. The ceremony goes back to the twelfth century and now works as a health check.

Swans defend a nest against people as readily as against a fox. A blow from the wing is painful and a bite from the bill is worse. Birds have knocked riders off jet skis and have attacked canoes near their young. An adult swan can seriously hurt a child. The old claim that a swan can break a man's leg is false.

In culture and myth

Greek writers held that each swan sings one time only, as it dies. Aeschylus put the image into Agamemnon in 458 BC, and Plato read that final song as joy. Aristotle called swans musical birds that sing near the end of life. Pliny the Elder rejected the story in AD 77 and said that watching swans proved it wrong. The whooper swan is the likely source, because a loop in its windpipe gives a long run of notes.

In Irish legend the four children of Lir spent 900 years as white swans. Their stepmother Aoife cursed them into three spells of 300 years on three waters. The tale ends with an order that protects every swan in Ireland from killing. Hans Christian Andersen wrote The Ugly Duckling about a cygnet rejected by farmyard birds. The story appears to turn on the moment the bird grows into a swan.

Denmark has named the mute swan its national bird since 1984. At Wells in England, swans on the palace moat learned to pull a string and ring for food. Two of the Wells birds can still ring for lunch. Boston keeps a pair in the Public Garden named Romeo and Juliet, and both turned out to be female. The Sydney Swans took the mute swan as a badge because it matched the club colours.