The mute swan (Cygnus olor) is a species of swan and a member of the family Anatidae within the waterfowl order. It is native to much of Europe and parts of Asia and (as a rare winter visitor) the far north of Africa. 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. The name "mute" derives from it being less vocal than other swan species. Typically measuring in length, this large swan is wholly white in plumage, with an orange beak bordered with black. It is recognisable by its pronounced knob atop the beak, which is larger in males.
Taxonomy The mute swan was first formally named by the German naturalist Johann Friedrich Gmelin as Anas olor in 1789 and was transferred by Johann Matthäus Bechstein to the new genus Cygnus in 1803. Both cygnus and olor mean 'swan' in Latin; cygnus is a variant form of cycnus, borrowing from Greek kyknos, a word of the same meaning., .
Despite its Eurasian origin, its closest relatives are the black swan of Australia and the black-necked swan of South America, not the other Northern Hemisphere swans of the genus Cygnus. The species is monotypic, with no living subspecies.
Evolution Mute swan subfossils, dating back 6,000 years, have been found in post-glacial peat beds of East Anglia, Great Britain. They have been recorded from Ireland east to Portugal and Italy, and from France, 13,000 BP (Desbrosse and Mourer-Chauvire 1972–1973). Cygnus olor bergmanni, a paleosubspecies 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.
Fossils of swan ancestors more distantly allied to the mute swan have been found in four U.S. states: California, Arizona, Idaho, and Oregon. The timeline runs from the Miocene to the late Pleistocene or 10,000 BP. The latest find was in Anza-Borrego Desert, a state park in California. Fossils from the Pleistocene include Cygnus paloregonus from Fossil Lake, Oregon, Froman's Ferry, Idaho, and Arizona, referred to by Howard in The Waterfowl of the World as "probably the mute type swan".
Description Adults of this large swan typically range from long, although they can range in extreme cases from , with a wingspan.Madge, Steve, Waterfowl: An Identification Guide to the Ducks, Geese, and Swans of the World. Houghton Mifflin Harcourt (1992), Mullarney, K., Svensson, L, Zetterstrom, D., & Grant, P.J. (1999) Collins Bird Guide. HarperCollins Publishers Ltd., London p. 14 Males are larger than females and have a larger knob on their bill. On average, this is the second largest waterfowl species after the trumpeter swan, although male mute swans can easily match or even exceed a male trumpeter in mass.del Hoyo, et al., Handbook of the Birds of the World. Volume 1: Ostrich to Ducks (Handbooks of the Birds of the World). Lynx Edicions (1992), Among standard measurements of the mute swan, the wing chord measures , the tarsus is , and the bill is . The plumage is white, while the legs are dark grey. The beak of the mute swan is bright orange, with black around the nostrils and a black nail.
The mute swan is one of the heaviest extant flying birds. In several studies from Great Britain, males (known as cobs) were found to average from about , with a weight range of , while the slightly smaller females (known as pens) averaged about , with a weight range of .CRC Handbook of Avian Body Masses by John B. Dunning Jr. (Editor). CRC Press (1992), .Sears, J. (1989). Feeding activity and body condition of mute swans Cygnus olor in rural and urban areas of a lowland river system. Wildfowl, 40(40), 88–98.Reynolds, C. M. (1972). Mute Swan weights in relation to breeding. Wildfowl, 23(23), 8.Bacon, P. J., & Coleman, A. E. (1986). An analysis of weight changes in the Mute Swan Cygnus olor. Bird Study, 33(3), 145–158. While the top normal weight for a big cob is roughly , one unusually big Polish cob weighed almost , and this counts as the largest weight ever verified for a flying bird, although it has been questioned whether this heavyweight could still take flight. Mute swans can achieve speeds in flight of up to 88.5 km/h (55 mph), and during takeoff they achieve speeds of around 48 km/h (30 mph) when running to gain lift.
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. The down may range from pure white to grey to buff, with grey/buff the most common. The white cygnets have a leucistic gene. Cygnets grow quickly, reaching a size close to their adult size in approximately three months after hatching. Cygnets typically retain their grey feathers until they are at least one year old, with the down on their wings having been replaced by flight feathers earlier that 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.
Polish swan
The colour morph C. o. morpha immutabilis (immūtābilis is Latin for "immutable, unchangeable, unalterable"), also known as the "Polish swan", has pinkish (not dark grey) legs and dull-white cygnets; as with white domestic geese, it is found only in populations with a history of domestication. Polish swans carry a copy of a gene responsible for leucism.
Behaviour Unlike black swans, mute swans are usually strongly territorial, with just a single pair on smaller lakes, though in a few locations where a large area of suitable feeding habitat is found, they can be colonial. The largest colonies have over 100 pairs, such as at the colony at Abbotsbury Swannery in Southern England and at the southern tip of Öland, Ottenby Preserve, in the coastal waters of the Baltic Sea; they can have nests spaced as little as apart. Non-mated juveniles up to 3–4 years old commonly form larger flocks, which can total several hundred birds, often at regular traditional sites. A notable flock of non-breeding birds is found on the River Tweed estuary at Berwick-upon-Tweed in Northeastern England, with a maximum count of 787 birds. A large population exists near the Swan Lifeline Station in Windsor and lives on the Thames in the shadow of Windsor Castle. Once the adults are mated, they seek out their territories and often live close to ducks and gulls, which may take advantage of the swan's ability to reach deep water weeds that tend to spread out on the water surface.
The mute swan is less vocal than the noisy whooper and tundra swans; they do, however, make a variety of sounds, often described as "grunting, hoarse whistling, and snorting noises". During a courtship display, mute swans utter a rhythmic song. The song helps synchronize the movements of their heads and necks; it could technically be employed to distinguish a bonded couple from two dating swans, as the rhythm of the song typically fails to match the pace of the head movements of two dating swans. Mute swans usually hiss at competitors or intruders trying to enter their territory. The most familiar sound associated with mute swans is the vibrant throbbing of the wings in flight, which is unique to the species and can be heard from a range of , indicating its value as a contact sound between birds in flight. Cygnets are especially vocal and communicate through a variety of whistling and chirping sounds when content, as well as a harsher chirping noise when distressed or lost.
Busking, a pose with the neck curved back and wings half raised, is a common threat display. Both feet are paddled in unison during this display, resulting in more jerky movement. The swans may also use the busking posture for wind-assisted transportation over several hundred meters, so-called windsurfing.
Diet They feed on a wide range of vegetation, both by reaching submerged aquatic plants with their long necks and by grazing on land. The food commonly includes agricultural crop plants such as oilseed rape and wheat, and in winter, feeding flocks may cause significant crop damage — often as much through trampling with their large webbed feet as through direct consumption. Mute swans also feed on small proportions of aquatic insects, fish, and frogs.
Breeding
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 are monogamous and often reuse the same nest each year, restoring or rebuilding it as needed. Male and female swans share the care of the nest, and once the cygnets are fledged, it is not uncommon to see whole families looking for food.
Clutch size is variable and is typically 5–8 eggs, latitude of nesting and time of year can affect clutch size. The eggs of this species measure in length and in width, with a mass of . One exceptionally large egg was over . The female broods for around 36 days, with cygnets normally hatching between May and July.
Cygnets hatch weighing . When very young, cygnets may climb onto the back of one of their parents if they become tired while on the water, with the adult proceeding to carry them around. Cygnets may also shelter beneath their parent's wings during periods of heavy rain as a means to stay warm and dry.
Mute swans can be very aggressive in defence of their nests and are highly protective of their mate and offspring. 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. Swans attack by striking at the threat with bony spurs in their wings, accompanied by biting with their large bill. Large waterfowl, such as Canada geese (more likely out of competition than in response to potential predation), may be aggressively driven off. Smaller waterbirds such as ducks are normally grabbed with the swan's bill and dragged or thrown clear of the swan and its offspring. Bird intruders into a swan's territory, such as other swans, geese, and ducks, may be killed by drowning, climbing onto and pecking at the back of the head to force the other bird underwater. The cob will sometimes attack small watercraft, such as canoes, that it feels are a threat to its young.
Young swans can fly 60–65 days after hatching, although they will fledge after 120–150 days. At fledging, birds will be 70–75% of their adult mass.
A 2026 study, conducted in Poland, indicated reduced reproductive output when native Mute Swans were placed in competition against Whooper Swans.
Predators and mortality
In their native range, wild boars and corvids such as hooded crows take eggs of mute swan.Krivonosov, G. A. (2013). Mute Swans Cygnus olor breeding in the Volga Delta, USSR. Wildfowl, 157-160. Red foxes, northern pike, and invasive American minks occasionally prey on cygnets.Minton, C. D. T. (1968). Pairing and breeding of Mute Swans. Wildfowl, 19(19), 41-60.Perrins, C. M., & Ogilvie, M. A. (1981). A study of the Abbotsbury mute swans. Wildfowl, 32(32), 35-47. In New York (outside of its native range), the most common predators of cygnets are common snapping turtles. The wings of the swan are very powerful, though not strong enough to break an adult man's leg, as is commonly misquoted. Nevertheless, they can and usually keep most predators at bay and even kill large predators such as red foxes.Whitehurst, David K. "Virginia Department of Game & Inland Fisheries." (2012).Porteus, T. A., Short, M. J., Hoodless, A. N., & Reynolds, J. C. (2024). Movement ecology and minimum density estimates of red foxes in wet grassland habitats used by breeding wading birds. European Journal of Wildlife Research, 70(1), 8.