There are 7 species of swan in the genus Cygnus; this includes the Whistling Swan (Cygnus columbianus columbianus) and Bewick’s Swan (Cygnus columbianus bewickii) as sister species which are sometimes grouped together as Tundra Swan. The Coscoroba Swan (Coscoroba coscoroba) is the 8th Species, but is no longer considered a true swan as it is thought to be closer related to geese, therefore it is in its own monotypic genus (Johnson, 2011).
Five of the Swan species are found in the Northern Hemisphere, these being the Whooper (Cygnus cygnus), Mute (Cygnus olor), Bewick’s (C. c. bewickii), Whistling (C. c. columbianus) and the Trumpeter (Cygnus buccinators); all are white in colour. The southern hemisphere swans are a mix of colouration with the all black Cygnus atratus, the black-necked Cygnus melanocoryphus and the white C. coscoroba.
Swans tend to pair for life and stay together throughout the year. There are a few exceptions, with the divorce rate estimated around 6% (Johnson, 2011). Mates have been observed to switch in all species if there has been a significant nesting failure or if the mate has been lost. A female will pair up again quickly, usually choosing a younger male (Johnson, 2011). Pairing for life holds many benefits, from raising clutches and learning opportunities for the young to mutual protection. Pairing for life is especially beneficial to the Bewick’s Swan which migrates an average 2,500km a year, reducing available time for pairing (Crane, 2014).
The Whooper, Tundra and Trumpeter swans are fully migratory species, whereas the Mute swan is a partial migrant, being resident in Western Europe but migratory in Eastern Europe and Asia. The Black swan is purely resident (Johnson, 2011).
Swans primarily feed on aquatic vegetation, using their feet in shallow waters to expose roots and shoots. They feed by upending and plunging their heads into the water. Their long necks give them the advantage to feed in deeper waters than most other waterfowl, reducing the competition for food. In winter months where aquatic food sources are limited, swans will also eat grasses and cereal crops such as wheat. Young cygnets will eat aquatic insect and crustaceans as they require more protein in their younger years. As they get older their diet advances to aquatic vegetation that their parents churn up whilst foraging, until they learn how to do it successfully themselves (Johnson, 2011).
Due to their large size, swans have few natural predators, their main threat is human activity; either in the form of degradation/destruction of habitat or hunting for meat and feathers. Use of lead shot in hunting is a contentious issue, with spent shot commonly ingested by waterfowl including swans – the toxic effects of which result in a slow and painful death.
Crane, L. (2014) The Truth About Swans. Available from: http://www.bbc.co.uk/earth/story/20141204-the-truth-about-swans [Accessed 8th February 2016]
Johnson, S. (2011) Swans: Bird Genus Cygnus. Available from: https://www.beautyofbirds.com/swans.htm [Accessed 8th February 2016]