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The Swan
A Swan
Swans, are of the genus Cygnus, and are birds of the family Anatidae, which also includes geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae.
There are six to seven species of swan in the genus Cygnus; in addition there is another species known as a swan, the Coscoroba Swan, although this species is no longer considered related to the true swans.
The swans are the largest members of the duck family Anatidae, and are amongst the largest flying birds, weighing up to 15 kilograms. Compared to the closely related geese they are both larger in size and have proportionally larger feet and necks. They also have a patch of unfeathered skin between the eyes and bill in adults. The sexes are alike in plumage, but males are generally bigger and heavier than females.
The Northern Hemisphere species of swan have pure white plumage but the Southern Hemisphere species are mixed black and white. The Australian Black Swan (Cygnus atratus) is completely black except for the white flight feathers on its wings; the chicks of black swans are light grey in colour, and there is the South American Black-necked Swan which has a neck in the colour its name indicates.
The legs of swans are normally a dark blackish grey colour, except for the two South American species, which have pink legs. Bill colour varies: the four subarctic species have black bills with varying amounts of yellow, and all the others are patterned red and black. The Mute Swan and Black-necked Swan have a lump at the base of the bill on the upper mandible.
The swans are generally found in temperate environments, rarely occurring in the tropics. Four (or five) species occur in the Northern Hemisphere, one species is found in Australia and New Zealand and a final species is distributed in southern South America. They are absent from tropical Asia, Central America, northern South America and the entirety of Africa. One species, the Mute Swan, has been introduced to North America, Australia and New Zealand.
Several species are migratory, either wholly or partly so. The Mute Swan is a partial migrant, being resident over areas of Western Europe but wholly migratory in Eastern Europe and Asia. The Whooper Swan and Tundra Swan are wholly migratory, and the Trumpeter Swans are almost entirely migratory. There is some evidence that the Black-necked Swan is migratory over part of its range, but detailed studies have not established whether these movements are long or short range migration.
Swans feed in the water and on land. They are almost entirely herbivorous, although small numbers of aquatic animals may be eaten. In the water, food is obtained by up-ending or dabbling, and their diet is composed of the roots, tubers, stems and leaves of aquatic and submerged plants.
Swans form monogamous pair bonds that last for many years. In many cases these pair bonds can last for life, but divorces between pairs do occur. These bonds are maintained year round, even in gregarious and migratory species like the Tundra Swan, which congregate in large flocks in the wintering grounds. Unlike many other ducks and geese the male helps with the nest construction. With the exception of the whistling-ducks they are the only anatids where the males aid in incubating the eggs.
Swans are included on the list which includes animals (birds, mammals, insects, fish etc.) for which there is documented evidence of homosexual or transgender behaviour of one or more of the following kinds: sex, courtship, affection, pair bonding, or parenting, as noted in researcher and author Julian Colton’s 1999 book Biological Exuberance: Animal Homosexuality and Natural Diversity.
All evidence suggests that the genus Cygnus evolved in Europe or western Eurasia during the Miocene, spreading all over the Northern Hemisphere until the Pliocene. When the southern species branched off is not known. The Mute Swan apparently is closest to the Southern Hemisphere Cygnus; its habits of carrying the neck curved (not straight) and the wings fluffed (not flush) as well as its bill colour and knob indicate that its closest living relative is actually the Black Swan.
Given the biogeography and appearance of the subgenus Olor it seems likely that these are of a more recent origin, as evidence shows by their modern ranges which were mostly uninhabitable during the last ice age.
(Source: Wikipedia – The Free Online encyclopedia)
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