Swans, genus Cygnus, are birds of the family Anatidae, which also includes geese and ducks. There are six or seven species of swan in the genus Cygnus; in addition there is another species known as the Coscoroba Swan, although this species is no longer considered one of the true swans.
The swans are the largest members of the waterfowl family Anatidae, and are among the largest flying birds. The largest species, including the mute swan, trumpeter swan, and whooper swan, can reach length of over 1.5 m and weigh over 15 kg. Their wingspans can be almost 3 m. Compared to the closely related geese they are much 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.
Bewick's Swan, (often considered a subspecies of the Tundra Swan)
The Northern Hemisphere species of swan have pure white plumage but the Southern Hemisphere species are mixed black and white. The Australian Black Swan is completely black except for the white flight feathers on its wings; the chicks of black swans are light grey in colour, and the South American Black-necked Swan has a black neck.
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. Although most birds generally do not have teeth, swans are known to be an exception to this, having small jagged 'teeth' as part of their beaks used for catching and eating fish. The Mute Swan and Black-necked Swan have a lump at the base of the bill on the upper mandible.
Swans feed in the water and on land. They are almost entirely herbivorous, although they may eat small amounts of aquatic animals. 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. In summer, the diet of swans consists mainly of aquatic vegetation, eaten while swimming, such as underwater plants and algae. They will eatgrasses found along the banks and are also insectivores so will eat small insects. At other times of year, they also eat cultivated grains in open fields.
Social and Reproductive
Although swans only reach sexual maturity between 4 and 7 years of age, they can form socially monogamous pair bonds from as early as 20 months that last for many years, and in some cases these can last for life. The lifespan of the mute swan is often over 10 years, and sometimes over 20, whereas the black-necked swan survives for less than a decade in captivity 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. The nest is on the ground near water and about a metre across. Unlike many other ducks and geese the male helps with the nest construction. Average egg size (for the mute swan) is 113×74 mm, weighing 340 g, in a clutch size of 4 to 7, and an incubation period of 34–45 days. With the exception of the whistling ducks they are the only anatids where the males aid in incubating the eggs.
Swans are known to aggressively protect their nests. One man is suspected to have drowned in such an attack.