The Dream Swan
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.
Swans form socially monogamous pair bonds that last for many years, and in some cases these can last for life. Modern genetic techniques are starting to reveal that 'divorces' are more common than previously thought, as is mating with other swans outside of the social pairing, without breaking the social pair bond. 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.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 (del Hoyo et al., eds, Handbook of the Birds of the World); its habits of carrying the neck curved (not straight) and the wings fluffed (not flush) as well as its bill color 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) and great similarity between the taxa.
Mute Swan, Cygnus olor, is a Eurasian species that occurs at lower latitudes than Whooper Swan and Bewick's Swan across Europe into southern Russia, China and the Russian Maritimes. Recent fossil records, according to the British Ornithological Union, show Cygnus olor is among the oldest bird species still extant and it has been upgraded to "native" species in several European countries, since this bird has been found in fossil and bog specimens dating back thousands of years. Common temperate Eurasian species, often semi-domesticated; descendants of domestic flocks are naturalized in the United States and elsewhere.
Cygnus atratus and cygnet.
Black-necked swan at WWT London Wetland Centre
Black Swan, Cygnus atratus of Australia, and introduced in New Zealand.
New Zealand Swan, Cygnus atratus sumnerensis, an extinct subspecies of the Black Swan from New Zealand and the Chatham Islands.
Black-necked Swan, Cygnus melancoryphus of South America.
Whooper Swan, Cygnus cygnus breeds in Iceland and subarctic Europe and Asia, migrating to temperate Europe and Asia in winter.
Trumpeter Swan, Cygnus buccinator is the largest North American swan. Very similar to the Whooper Swan (and sometimes treated as a subspecies of it), it was hunted almost to extinction but has since recovered.
Tundra Swan, Cygnus columbianus is a small swan which breeds on the North American tundra, further north than Trumpeter Swan. It winters in the USA.
Bewick's Swan, Cygnus (columbianus) bewickii is the Eurasian form which migrates from Arctic Russia to western Europe and eastern Asia (China, Japan) in winter. It is often considered a subspecies of C. columbianus, creating the species Tundra Swan.
The fossil record of the genus Cygnus is quite impressive, although allocation to the subgenera is often tentative; as indicated above, at least the early forms probably belong to the C. olor - Southern Hemisphere lineage, whereas the Pleistocene taxa from North America would be placed in Olor. A number of prehistoric species have been described, mostly from the Northern Hemisphere. Among them was the giant Siculo-Maltese C. falconeri which was taller (though not heavier) than the contemporary local dwarf elephants (Elephas falconeri).
February 26th, 2012
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