AppearanceAdults of this large swan typically range from 140 to 160 cm long, although can range in extreme cases from 125 to 170 cm, with a 200 to 240 cm wingspan. 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. Among standard measurements of the mute swan, the wing chord measures 53–62.3 cm, the tarsus is 10–11.8 cm and the bill is 6.9–9 cm.
The mute swan is one of the heaviest flying birds. In several studies from Great Britain, males were found to average from about 10.6 to 11.87 kg, with a weight range of 9.2–14.3 kg while the slightly smaller females averaged about 8.5 to 9.67 kg, with a weight range of 7.6–10.6 kg.
While the top normal weight for a big cob is roughly 15 kg, one unusually big Polish cob weighed almost 23 kg 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.
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. All mute swans are white at maturity, though the feathers are often stained orange-brown by iron and tannins in the water.
The morph ''immutabilis'' has pinkish legs and dull white cygnets; as with white domestic geese, it is only found in populations with a history of domestication. Polish swans carry a copy of a gene responsible for leucism.
DistributionThe mute swan is found naturally mainly in temperate areas of Europe across western Asia, as far east as the Russian Maritimes, near Sidemi.
BehaviorMute 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.
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 mute swan is less vocal than the noisy whooper and Bewick's swans; they do, however, make a variety of grunting, hoarse whistling, and snorting noises, especially in communicating with their cygnets, and usually hiss at competitors or intruders trying to enter their territory.
ReproductionMute swans lay an average of four eggs, and the female broods for 36 days. The cygnets do not reach the ability of flight before an age of 120 to 150 days: this limits the distribution of the species in the northern edge of its range, as the cygnets must learn to fly before the waters freeze.
FoodThey feed on a wide range of vegetation, both submerged aquatic plants which they reach with their long necks, and by grazing on land. The food commonly includes agricultural crop plants such as oilseed rape and wheat, and feeding flocks in the winter may cause significant crop damage, often as much through trampling with their large webbed feet, as through direct consumption.
EvolutionMute swan subfossils, 6,000 years old, 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 . The paleosubspecies ''Cygnus olor bergmanni'', which differed only in size from the living bird, is known from fossils found in Azerbaijan.
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 national 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".
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