It is an introduced species in North America, home to the largest populations outside of its native range, with additional smaller introductions in Australasia and southern Africa.

[2][3][4] Measuring 125 to 160 cm (49 to 63 in) in length, this large swan is wholly white in plumage with an orange beak bordered with black.

[2][4] Mute swan subfossils, 6,000 years old, have been found in post-glacial peat beds of East Anglia, Great Britain.

Cygnus olor bergmanni, a paleosub species that differed only in size from the living bird, is known from fossils found in Azerbaijan.

A related paleospecies recorded from fossils and subfossils is the Giant swan, Cygnus falconeri, a flightless species that lived on the islands of Malta and Sicily during the Middle Pleistocene.

[21] Young birds, called cygnets, are not the bright white of mature adults, and their bill is dull greyish-black, not orange, for the first year.

All mute swans are white at maturity, though the feathers (particularly on the head and neck) are often stained orange-brown by iron and tannins in the water.

[24] Mute swans nest on large mounds that they build with waterside vegetation in shallow water on islands in the middle or at the very edge of a lake.

They feed on a wide range of vegetation, both submerged aquatic plants which they reach with their long necks, and by grazing on land.

[23][27] Non-mated juveniles up to 3–4 years old commonly form larger flocks, which can total several hundred birds, often at regular traditional sites.

Most defensive acts from a mute swan begin with a loud hiss and, if this is not sufficient to drive off the predator or intruder, are followed by a physical attack.

[33] Large waterfowl, such as Canada geese (more likely out of competition than in response to potential predation), may be aggressively driven off, and mute swans regularly attack people who enter their territory.

[34] The cob is responsible for defending the cygnets while on the water, and will sometimes attack small watercraft, such as canoes, that it feels are a threat to its young.

Cygnets may also shelter beneath their parent's wings during periods of heavy rain as a means to stay warm and dry.

[45][46] Swans will go through a mourning process, and in the case of the loss of their mate, may either stay where their counterpart lived or fly off to join a flock.

This limits the distribution of the species at the northern edge of its range as the cygnets need to learn to fly before the ponds and lakes freeze over.

[citation needed] The mute swan is found naturally mainly in temperate areas of Europe, then across the Palearctic as far east as Primorsky Krai, near Sidemi.

[citation needed] The total native population of mute swans is about 500,000 birds at the end of the breeding season (adults plus young), of which up to 350,000 are in Russia.

[3] For many centuries, mute swans in Great Britain were domesticated for food, with individuals being marked by nicks on their webs (feet) or beaks to indicate ownership.

After lead weights and shot were mostly replaced by other less toxic alternatives, mute swan numbers increased again rapidly.

[3] Since being introduced into North America, the mute swan has increased greatly in number to the extent that it is considered an invasive species there.

Recently, it has been widely viewed as an invasive species because of its rapidly increasing numbers and its adverse effects on other waterfowl and native ecosystems.

Fish and Wildlife Service proposed to "minimize environmental damages attributed to Mute Swans" by reducing their numbers in the Atlantic Flyway to pre-1986 levels, a 67% reduction at the time.

At this time mute swans were protected under the Migratory Bird Treaty Act due to a court order, but in 2005 the United States Department of the Interior officially declared them a non-native, unprotected species.

[64] The fairy tale "The Ugly Duckling" by Hans Christian Andersen tells the story of a cygnet ostracised by his fellow barnyard fowl because of his perceived unattractiveness.

[67] The pair of swans in the Boston Public Garden are named Romeo and Juliet after the Shakespearean couple; however, it was found that both of them are females.