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Bewick's Swan

Bewick's Swan

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Encyclopedia
The Tundra Swan is a small Holarctic
Holarctic
The Holarctic ecozone refers to the habitats found throughout the northern continents of the world as a whole. This region is divided into the Palearctic, consisting of Northern Africa and all of Eurasia, with the exception of Southeast Asia and the Indian subcontinent, and the Nearctic,...

 swan
Swan
Swans, genus Cygnus, 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...

. The two taxa within it are usually regarded as conspecific, but are also sometimes split into two species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, Cygnus bewickii (Bewick's Swan) of the Palaearctic and the Whistling Swan, C. columbianus proper, of the Nearctic
Nearctic
The Nearctic is one of the eight terrestrial ecozones dividing the Earth's land surface.The Nearctic ecozone covers most of North America, including Greenland and the highlands of Mexico...

. Birds from eastern Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

 (roughly east of the Taimyr Peninsula) are sometimes separated as the subspecies C. c. jankowskii, but this is not widely accepted as distinct, most authors including them in C. c. bewickii. Tundra Swans are sometimes separated in the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Olor together with the other Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

 swan species.

Bewick's Swan is named after the engraver Thomas Bewick
Thomas Bewick
Thomas Bewick was an English wood engraver and ornithologist.- Early life and apprenticeship :Bewick was born at Cherryburn House in the village of Mickley, in the parish of Ovingham, Northumberland, England, near Newcastle upon Tyne on 12 August 1753...

, who specialised in illustrations of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s and animals.

Description


C. columbianus is the smallest of the Holarctic
Holarctic
The Holarctic ecozone refers to the habitats found throughout the northern continents of the world as a whole. This region is divided into the Palearctic, consisting of Northern Africa and all of Eurasia, with the exception of Southeast Asia and the Indian subcontinent, and the Nearctic,...

 swans, at 115–150 cm (45.3–59.1 in) in length, 168–211 cm (66.1–83.1 in) in wingspan and a weight range of 3.4–9.6 kg (7.5–21.2 lb). In adult birds, the plumage of both subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

 is entirely white, with black feet, and a bill that is mostly black, with a thin salmon-pink streak running along the mouthline and – depending on the subspecies – more or less yellow in the proximal part. The iris
Iris (anatomy)
The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...

 is dark brown. In birds living in waters that contains large amounts of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s (e.g. bog
Bog
A bog, quagmire or mire is a wetland that accumulates acidic peat, a deposit of dead plant material—often mosses or, in Arctic climates, lichens....

 lakes), the head and neck plumage acquires a golden or rusty hue. Pens (females) are slightly smaller than cobs (males), but do not differ in appearance otherwise.


Immatures of both subspecies are white mixed with some dull grey feathering, mainly on the head and upper neck, which are often entirely light grey; their first-summer plumage is quite white already, and in their second winter they moult
Moult
In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...

 into the adult plumage. Their bills are black with a large dirty-pink patch taking up most of the proximal half and often black nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...

s, and their feet are dark grey with a pinkish hue. Downy
Down feather
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator and padding, used in goods such as jackets, bedding,...

 young are silvery grey above and white below.

Bewick's Swans are the smaller subspecies. There is a slight size cline
Cline (population genetics)
In biology, an ecocline or simply cline describes an ecotone in which a series of biocommunities display continuous gradient...

, with the eastern birds being slightly larger; good measurement data only exists for the western populations however. These weigh 3.4–7.8 kg (7.5–17.2 lb), 6.4 kilograms (14.1 lb) on average in males and 5.7 kilograms (12.6 lb) in females. They measure 115–140 cm (45.3–55.1 in) in overall length; each wing is 46.9–54.8 cm (18.5–21.6 in) long, on average 51.9 centimetres (20.4 in) in males and 50.4 centimetres (19.8 in) in females. The tarsus
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...

 measures 9.2–11.6 cm (3.6–4.6 in) in length, the bill 8.2–10.2 cm (3.2–4 in), averaging 9.1 centimetres (3.6 in). Bewick's Swan is similar in appearance to the parapatric Whooper Swan
Whooper Swan
The Whooper Swan , Cygnus cygnus, is a large Northern Hemisphere swan. It is the Eurasian counterpart of the North American Trumpeter Swan. An old name for the Whooper Swan is Elk; it is so called in Francis Willughby and John Ray's Ornithology of 1676.-Description:The Whooper Swan is similar in...

 (C. cygnus), but is smaller, shorter-necked and has a more rounded head shape, with variable bill
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...

 pattern, but always showing more black than yellow and having a blunt forward edge of the yellow base patch. Whooper Swans have a bill that has more yellow than black and the forward edge of the yellow patch is usually pointed. The bill pattern for every individual Bewick's Swan is unique, and scientists often make detailed drawings of each bill and assign names to the swans to assist with studying these bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s. The eastern birds, apart from being larger, tend towards less yellow on the bill, perhaps indicating that gene flow
Gene flow
In population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...

 across Beringia, while marginal, never entirely ceased. An apparent case of hybridization between a Bewick's and a vagrant Whistling Swan has been reported from eastern Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

.



Whistling Swans weigh 9.5–21 lb (4.3–9.5 kg) – 16 pounds (7.3 kg) on average in males and 14 pounds (6.4 kg) in females –, and measure 47–59 in (119.4–149.9 cm) in length. Each wing is 19.7–22.4 in (50–56.9 cm) long; the tarsus measures 3.7–4.5 in (9.4–11.4 cm) in length, and the bill is 3.6–4.2 in (9.1–10.7 cm) long. C. c. columbianus is distinguished from C. c. bewickii by its larger size and the mostly black bill, with just a small and usually hard to see yellow spot of variable size at the base. It is distinguished from the largely allopatric Trumpeter Swan
Trumpeter Swan
The Trumpeter Swan, Cygnus buccinator, is the largest native North American bird, if measured in terms of weight and length, and is the largest living waterfowl species on earth. It is the North American counterpart of the European Whooper Swan.-Description:Males typically measure from and weigh...

 (C. buccinator) of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 by that species' much larger size and particularly long bill, which is black all over except for the pink mouthline, which is stronger than in the Whistling Swan.

Note that color variations with more or less yellow, or pink instead of yellow or black, are not exceptional, especially in Bewick's Swans, which very rarely may even have yellowish feet. The small size and particularly the rather short neck, which make it look like a large white goose
Goose
The word goose is the English name for a group of waterfowl, belonging to the family Anatidae. This family also includes swans, most of which are larger than true geese, and ducks, which are smaller....

, are still distinguishing marks.

Tundra Swans have high-pitched honking calls and sound similar to a black goose (Branta). They are particularly vocal when foraging in flocks on their wintering grounds; any conspecific arriving or leaving will elicit a bout of loud excited calling from its fellows. Contrary to its common name, the ground calls of the Whistling Swan are not a whistle and neither notably different from that of Bewick's Swan. The flight call of the latter is a low and soft ringing bark, bow-wow...; the Whistling Swan gives a markedly high-pitched trisyllabic bark like wow-wow-wow in flight. By contrast, the Whooper and Trumpeter Swans' names accurately describe their calls – a deep hooting and a higher-pitched French horn-like honk, respectively. Flying birds of these species are shorter-necked and have a quicker wingbeat than their relatives, but they are often impossible to tell apart except by their calls.

Distribution



As their common name implies, the Tundra Swan breeds in the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

 and subarctic
Subarctic
The Subarctic is a region in the Northern Hemisphere immediately south of the true Arctic and covering much of Alaska, Canada, the north of Scandinavia, Siberia, and northern Mongolia...

 tundra
Tundra
In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...

, where they inhabit shallow pool
Stream pool
A stream pool, in hydrology, is a stretch of a river or stream in which the water depth is above average and the water velocity is quite below average.-Formation:...

s, lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

s and rivers. These birds, unlike Mute Swans (C. olor) but like the other Arctic swans, are migratory birds
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...

. The winter habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

 of both subspecies is grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...

 and marshland, often near the coast; they like to visit fields after harvest to feed on discarded grains and while on migration may stop over on mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

 lakes. According to National Geographic, when migrating these birds can fly at altitudes of 8 km (nearly 27,000 ft); Tundra Swan flocks usually fly in V formation.

The breeding range of C. c. bewickii extends across the coastal lowlands of Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

, from the Kola Peninsula
Kola Peninsula
The Kola Peninsula is a peninsula in the far northwest of Russia. Constituting the bulk of the territory of Murmansk Oblast, it lies almost completely to the north of the Arctic Circle and is washed by the Barents Sea in the north and the White Sea in the east and southeast...

 east to the Pacific. They start to arrive on the breeding grounds around mid-May, and leave for winter quarters around the end of September. The populations west of the Taimyr Peninsula migrate via the White Sea
White Sea
The White Sea is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the northeast. The whole of the White Sea is under Russian sovereignty and considered to be part of...

, Baltic Sea
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...

 and the Elbe
Elbe
The Elbe is one of the major rivers of Central Europe. It rises in the Krkonoše Mountains of the northwestern Czech Republic before traversing much of Bohemia , then Germany and flowing into the North Sea at Cuxhaven, 110 km northwest of Hamburg...

 estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

 to winter in Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...

, the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

 and the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...

. They are common in winter in the wildfowl nature reserve
Nature reserve
A nature reserve is a protected area of importance for wildlife, flora, fauna or features of geological or other special interest, which is reserved and managed for conservation and to provide special opportunities for study or research...

s of the Royal Society for the Protection of Birds
Royal Society for the Protection of Birds
Bird Notes and News was first published in April 1903.The title changed to 'Bird Notes' in 1947. In the 1950s, there were four copies per year . Each volume covered two years, spread over three calendar years...

 and of the Wildfowl and Wetlands Trust
Wildfowl and Wetlands Trust
The Wildfowl & Wetlands Trust is a wildfowl and wetland conservation charity in the United Kingdom. Its patron is Queen Elizabeth II.It was founded in 1946 by the ornithologist and artist Sir Peter Scott, initially as the Severn Wildfowl Trust...

. Some birds also winter elsewhere on the southern shores of the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

. Bewick's Swans breeding in eastern Russia migrate via Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...

 and northern China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 to winter in the coastal regions of Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, and southern China, south to Guangdong
Guangdong
Guangdong is a province on the South China Sea coast of the People's Republic of China. The province was previously often written with the alternative English name Kwangtung Province...

 and occasionally as far as Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

. A few birds from the central Siberian range also winter in Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 at the south of the Caspian Sea
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...

; in former times these flocks also migrated to the Aral Sea
Aral Sea
The Aral Sea was a lake that lay between Kazakhstan in the north and Karakalpakstan, an autonomous region of Uzbekistan, in the south...

 before the late 20th century ecological catastrophe turned most of the habitat there into inhospitable wasteland. Arrival in winter quarters starts about mid-October, though most spend weeks or even months at favorite resting locations and will only arrive in winter quarters by November or even as late as January
January
January is the first month of the year in the Julian and Gregorian calendars and one of seven months with the length of 31 days. The first day of the month is known as New Year's Day...

. The birds leave winter quarters to breed starting in mid-February. Vagrants may occur south of the main wintering range in cold years and have been recorded from most Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an countries where the birds do not regularly winter, as well as Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...

, NW India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, Iraq
Iraq
Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....

, Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

, Libya
Libya
Libya is an African country in the Maghreb region of North Africa bordered by the Mediterranean Sea to the north, Egypt to the east, Sudan to the southeast, Chad and Niger to the south, and Algeria and Tunisia to the west....

, Nepal
Nepal
Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...

, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...

, and on the Marianas and Volcano Islands
Volcano Islands
The Volcano Islands is a group of three Japanese islands south of the Bonin Islands that belong to the municipality of Ogasawara...

 in the western Pacific. Vagrants on the spring migration have been sighted on Bear Island, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

 and Svalbard
Svalbard
Svalbard is an archipelago in the Arctic, constituting the northernmost part of Norway. It is located north of mainland Europe, midway between mainland Norway and the North Pole. The group of islands range from 74° to 81° north latitude , and from 10° to 35° east longitude. Spitsbergen is the...

, and in Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

, Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

 and Sasketchewan in North America.

C. c. columbianus breeds in the coastal plains of Alaska and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, leaving for winter quarters about October. They arrive in winter quarters by November/December. Birds breeding in western Alaska winter along the Pacific coast from southern Alaska to California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

; they often move inland – particularly to the rich feeding grounds in the Californian Central Valley – and some cross the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...

 again and winter as far east as Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

 and south to Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

 and northern Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. The birds breeding along the Arctic Ocean
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...

 coast migrate via Canada and the Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...

 region to winter at the Atlantic coast of the USA, mainly from Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

 to South Carolina
South Carolina
South Carolina is a state in the Deep South of the United States that borders Georgia to the south, North Carolina to the north, and the Atlantic Ocean to the east. Originally part of the Province of Carolina, the Province of South Carolina was one of the 13 colonies that declared independence...

, but some move as far south as Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

. Whistling Swans start leaving for the breeding grounds again by mid-March, and arrive by late May. Vagrants have been recorded on the Bermudas, Cuba
Cuba
The Republic of Cuba is an island nation in the Caribbean. The nation of Cuba consists of the main island of Cuba, the Isla de la Juventud, and several archipelagos. Havana is the largest city in Cuba and the country's capital. Santiago de Cuba is the second largest city...

 the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...

, Puerto Rico
Puerto Rico
Puerto Rico , officially the Commonwealth of Puerto Rico , is an unincorporated territory of the United States, located in the northeastern Caribbean, east of the Dominican Republic and west of both the United States Virgin Islands and the British Virgin Islands.Puerto Rico comprises an...

, and in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

, Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, northeastern Siberia and Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

.

Ecology



In summer, their diet consists mainly of aquatic vegetation – e.g. mannagrass (Glyceria), Potamogeton
Potamogeton
Potamogeton is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae. Most are known by the common name pondweed, although many unrelated plants may be called pondweed, such as Canadian pondweed...

pondweeds and marine eelgrass (Zostera), acquired by sticking the head underwater or upending while swimming; they also eat some grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...

 growing on dry land. At other times of year, leftover grain
GRAIN
GRAIN is a small international non-profit organisation that works to support small farmers and social movements in their struggles for community-controlled and biodiversity-based food systems. Our support takes the form of independent research and analysis, networking at local, regional and...

s and other crop
Crop
Crop may refer to:* Crop, a plant grown and harvested for agricultural use* Crop , part of the alimentary tract of some animals* Crop , a modified whip used in horseback riding or disciplining humans...

s such as potato
Potato
The potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...

es, picked up in open fields after harvest, make up much of their diet. Tundra Swans forage mainly by day. In the breeding season, they tend to be territorial and are aggressive to many animals who pass by; outside the breeding season they are rather gregarious birds.

Healthy adult birds have few natural predators. Arctic Fox
Arctic fox
The arctic fox , also known as the white fox, polar fox or snow fox, is a small fox native to Arctic regions of the Northern Hemisphere and is common throughout the Arctic tundra biome. The Greek word alopex, means a fox and Vulpes is the Latin version...

es (Vulpes lagopus) may threaten breeding females and particular the eggs and hatchlings; they can be quite hard to scare away. Raccoon
Raccoon
Procyon is a genus of nocturnal mammals, comprising three species commonly known as raccoons, in the family Procyonidae. The most familiar species, the common raccoon , is often known simply as "the" raccoon, as the two other raccoon species in the genus are native only to the tropics and are...

s (Procyon lotor), very common in Canada, East Asia
East Asia
East Asia or Eastern Asia is a subregion of Asia that can be defined in either geographical or cultural terms...

 and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, eat eggs and young on occasion. About 15% of the adults die each year from various causes, and thus the average lifespan in the wild is about 10 years. The oldest recorded Tundra Swan was over 24 years old.

Reproduction


The Tundra Swans mate in the late spring, usually after they have returned to the nesting
Nesting
Nesting refers to the process of efficiently manufacturing parts from flat raw material.Companies manufacturing parts from flat raw material such as sheet metal use a variety of technologies to perform this task. The sheet metal nesting for flat sheets and nesting for coils are different algorithms...

 grounds; as usual for swans, they pair monogamously until one partner dies. Should one partner die long before the other, the surviving bird often will not mate again for some years, or even for its entire life. The nesting season starts at the end of May. The pair build the large mound-shaped nest from plant material at an elevated site near open water, and defend a large territory around it. The pen (female) lays and incubates a clutch
Clutch (eggs)
A clutch of eggs refers to all the eggs produced by birds or reptiles, often at a single time, particularly those laid in a nest.In birds, destruction of a clutch by predators, , results in double-clutching...

 of 2-7 (usually 3-5) eggs, watching for danger while sitting on the nest. The cob (male) keeps a steady lookout for potential predators heading towards his mate and offspring. When either of them spots a threat, they give a warning sound to let their partner know that danger is approaching. Sometimes the cob will use his wings to run faster and appear larger in order to scare away a predator.

The time from laying to hatching is 29–30 days for Bewick's Swan and 30–32 days for the Whistling Swan. Since they nest in cold regions, Tundra Swan cygnets grow faster than those of swans breeding in warmer climates; those of the Whistling Swan take about 60–75 days to fledge – twice as fast as those of the Mute Swan for example – while those of Bewick's Swan, about which little breeding data is known, may fledge a record 40–45 days after hatching already. The fledglings stay with their parents for the first winter migration. The family is sometimes even joined by their offspring from previous breeding seasons while on the wintering grounds; Tundra Swans do not reach sexual maturity until 3 or 4 years of age.

Conservation status


The Whistling Swan is the most common swan species of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

, estimated to number almost 170,000 individuals around 1990. Its numbers seem to be slowly declining in the west of its range since the late 19th century, coincident with the expansion of human settlement and habitat conversion in the birds' wintering areas; the eastern Whistling Swan populations on the other hand seem to be increasing somewhat, and altogether its numbers seem to have slightly risen in the late 20th century (the population was estimated at about 146,000 in 1972). Bewick's Swan remains far less known; the European winter population was estimated at 16,000-17,000 about 1990, with about 20,000 birds wintering in East Asia
East Asia
East Asia or Eastern Asia is a subregion of Asia that can be defined in either geographical or cultural terms...

. The Iranian wintering population is small – 1,000 birds or so at most – but they usually disperse to several sites, some of which are still unknown to scientists.

Although Tundra Swan numbers are stable over most of its range, they are increasingly dependent on agricultural crop
Crop
Crop may refer to:* Crop, a plant grown and harvested for agricultural use* Crop , part of the alimentary tract of some animals* Crop , a modified whip used in horseback riding or disciplining humans...

s to supplement their winter diet, as aquatic vegetation in their winter habitat dwindles due to habitat destruction
Habitat destruction
Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...

 and water pollution
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....

. But the main cause of adult mortality is hunting; 4,000 Whistling Swans are bagged officially each year, while a further 6,000-10,000 are killed by poacher
Poacher
Poacher may refer to:*One who engages in poaching, the theft or illegal killing of animals or plants*A device used for poaching *Poacher , a family of fish...

s and native subsistence hunter-gatherers. Bewick's Swan cannot be hunted legally, but almost half the birds studied contained lead shot
Lead shot
Lead shot is a collective term for small balls of lead. These were the original projectiles for muskets and early rifles, but today lead shot is fired primarily from shotguns. It is also used for a variety of other purposes...

 in their body, indicating they were shot at by poachers. Lead poisoning
Lead poisoning
Lead poisoning is a medical condition caused by increased levels of the heavy metal lead in the body. Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems...

 by ingestion of lead shot is a very significant cause of mortality also, particularly in the Whistling Swan. The Tundra Swan is not considered threatened by the IUCN due to its large range and population. The proposed subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

 jankowskii was for some time placed on CITES Appendix II; it was eventually removed since it is not generally accepted as valid.

Bewick's Swan is one of the birds to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA
AEWA
The Agreement on the Conservation of African-Eurasian Migratory Waterbirds is the largest of its kind developed so far under the Bonn Convention. It was concluded on 16 June 1995 at The Hague, the Netherlands and entered into force on 1 November 1999 after the required number of at least fourteen...

) applies.

Toxic mining wastes in the Silver Valley, Idaho in the United States is responsible for the death of migrating tundra swans.

Further reading


External links