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The tundra swan (''Cygnus columbianus'') is a small
swan Swans are birds of the family Anatidae within the genus ''Cygnus''. The swans' closest relatives include the geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometim ...
of the
Holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical regi ...
. The two
taxa In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...
within it are usually regarded as
conspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organ ...
, but are also sometimes split into two
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
: Bewick's swan (''Cygnus bewickii'') of the
Palaearctic The Palearctic or Palaearctic is the largest of the eight biogeographic realms of the Earth. It stretches across all of Eurasia north of the foothills of the Himalayas, and North Africa. The realm consists of several bioregions: the Euro-Si ...
and the whistling swan (''C. columbianus'') proper of the
Nearctic The Nearctic realm is one of the eight biogeographic realms constituting the Earth's land surface. The Nearctic realm covers most of North America, including Greenland, Central Florida, and the highlands of Mexico. The parts of North America ...
. Birds from eastern Russia (roughly east of the
Taymyr Peninsula The Taymyr Peninsula (russian: Таймырский полуостров, Taymyrsky poluostrov) is a peninsula in the Far North of Russia, in the Siberian Federal District, that forms the northernmost part of the mainland of Eurasia. Administrat ...
) are sometimes separated as the subspecies ''C. c. jankowskii'', but this is not widely accepted as distinct, with most authors including them in ''C. c. bewickii''. Tundra swans are sometimes separated in the
subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed betw ...
''Olor'' together with the other
Arctic The Arctic ( or ) is a polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada ( Yukon, Northwest Territories, Nunavut), Danish Realm ( Greenland), Finland, Iceland ...
swan species. Bewick's swan was named in 1830 by
William Yarrell William Yarrell (3 June 1784 – 1 September 1856) was an English zoologist, prolific writer, bookseller and naturalist admired by his contemporaries for his precise scientific work. Yarrell is best known as the author of ''The History of ...
after the engraver Thomas Bewick, who specialised in illustrations of birds and animals. ''Cygnus'' is the Latin for "swan", and '' columbianus'' comes from the Columbia River, the
type locality Type locality may refer to: * Type locality (biology) * Type locality (geology) See also * Local (disambiguation) * Locality (disambiguation) {{disambiguation ...
.


Description

''C. columbianus'' is the smallest of the
Holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical regi ...
swans, at in length, in wingspan and a weight range of . In adult birds, the plumage of both subspecies 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 Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position ...
part. The iris is dark brown. In birds living in waters that contains large amounts of iron ions (e.g.
bog A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; a ...
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 In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
into the adult plumage. Their bills are black with a large dirty-pink patch taking up most of the proximal half and often black nostrils, and their feet are dark grey with a pinkish hue.
Downy Downy, also known as Lenor in Europe, Russia and Japan, is a brand of fabric softener produced by Procter & Gamble that was introduced in 1960. Lenor is a brand name of fabric softener and dryer sheets, also produced by P&G, sold in Europe, Ru ...
young are silvery grey above and white below. Bewick's swans are the smaller subspecies. There is a slight size cline, with the eastern birds being slightly larger; good measurement data only exists for the western populations however. These weigh , on average in males and in females. They measure in overall length; each wing is long, on average in males and in females. The tarsus measures in length, the bill , averaging . Bewick's swan is similar in appearance to the parapatric
whooper swan The whooper swan ( /ˈhuːpə(ɹ) swɒn/) (''Cygnus cygnus''), also known as the common swan, pronounced ''hooper swan'', is a large northern hemisphere swan. It is the Eurasian counterpart of the North American trumpeter swan, and the type specie ...
(''C. cygnus''), but is smaller, shorter-necked and has a more rounded head shape, with variable bill 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 birds. The eastern birds, apart from being larger, tend towards less yellow on the bill, perhaps indicating that
gene flow In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalen ...
across
Beringia Beringia is defined today as the land and maritime area bounded on the west by the Lena River in Russia; on the east by the Mackenzie River in Canada; on the north by 72 degrees north latitude in the Chukchi Sea; and on the south by the tip ...
, 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 ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part o ...
. Whistling swans weigh – on average in males and in females –, and measure in length. Each wing is long; the tarsus measures in length, and the bill is 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 Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...
trumpeter swan The trumpeter swan (''Cygnus buccinator'') is a species of swan found in North America. The heaviest living bird native to North America, it is also the largest extant species of waterfowl, with a wingspan of 185 to 250 cm (6 ft 2 in to 8 ft 2 ...
(''C. buccinator'') of North America 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 A goose (plural, : geese) is a bird of any of several waterfowl species in the family (biology), family Anatidae. This group comprises the genera ''Anser (bird), Anser'' (the grey geese and white geese) and ''Branta'' (the black geese). Some o ...
, 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 Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organ ...
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 The French horn (since the 1930s known simply as the horn in professional music circles) is a brass instrument made of tubing wrapped into a coil with a flared bell. The double horn in F/B (technically a variety of German horn) is the horn most ...
-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
tundra In physical geography, tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. The term ''tundra'' comes through Russian (') from the Kildin Sámi word (') meaning "uplands", "treeless mo ...
of the
Arctic The Arctic ( or ) is a polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada ( Yukon, Northwest Territories, Nunavut), Danish Realm ( Greenland), Finland, Iceland ...
and subarctic, where they inhabit shallow pools, lakes and rivers. These birds, unlike
mute swan The mute swan (''Cygnus olor'') is a species of swan and a member of the waterfowl family Anatidae. It is native to much of Eurosiberia, and (as a rare winter visitor) the far north of Africa. It is an introduced species in North America, ho ...
s (''C. olor'') but like the other Arctic swans, are
migratory birds Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate. Migration carries high costs in predation and mortality, including from hunting ...
. The winter
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
of both subspecies is
grassland A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natur ...
and
marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found a ...
land, 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 lakes. According to '' National Geographic'', when migrating these birds can fly at altitudes of in a V formation. The breeding range of ''C. c. bewickii'' extends across the coastal lowlands of
Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part o ...
, from the
Kola Peninsula sjd, Куэлнэгк нёа̄ррк , image_name= Kola peninsula.png , image_caption= Kola Peninsula as a part of Murmansk Oblast , image_size= 300px , image_alt= , map_image= Murmansk in Russia.svg , map_caption = Location of Murmansk Oblast ...
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
Taymyr Peninsula The Taymyr Peninsula (russian: Таймырский полуостров, Taymyrsky poluostrov) is a peninsula in the Far North of Russia, in the Siberian Federal District, that forms the northernmost part of the mainland of Eurasia. Administrat ...
migrate via the
White Sea The White Sea (russian: Белое море, ''Béloye móre''; Karelian and fi, Vienanmeri, lit. Dvina Sea; yrk, Сэрако ямʼ, ''Serako yam'') is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is s ...
,
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and fr ...
and the
estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...
of the
Elbe The Elbe (; cs, Labe ; nds, Ilv or ''Elv''; Upper and dsb, Łobjo) is one of the major rivers of Central Europe. It rises in the Giant Mountains of the northern Czech Republic before traversing much of Bohemia (western half of the Czech Rep ...
to winter in Denmark, the Netherlands and the
British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles (O ...
. They are common in winter in the wildfowl
nature reserve A nature reserve (also known as a wildlife refuge, wildlife sanctuary, biosphere reserve or bioreserve, natural or nature preserve, or nature conservation area) is a protected area of importance for flora, fauna, or features of geological or ...
s of the
Royal Society for the Protection of Birds The Royal Society for the Protection of Birds (RSPB) is a charitable organisation registered in England and Wales and in Scotland. It was founded in 1889. It works to promote conservation and protection of birds and the wider environment throu ...
and of the Wildfowl & Wetlands Trust. Some birds also winter elsewhere on the southern shores of the
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...
. Bewick's swans breeding in eastern Russia migrate via Mongolia and northern China to winter in the coastal regions of Korea, Japan, and southern China, south to
Guangdong Guangdong (, ), alternatively romanized as Canton or Kwangtung, is a coastal province in South China on the north shore of the South China Sea. The capital of the province is Guangzhou. With a population of 126.01 million (as of 2020 ...
and occasionally as far as Taiwan. A few birds from the central Siberian range also winter in Iran at the south of the
Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the List of lakes by area, world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad s ...
; in former times these flocks also migrated to the
Aral Sea The Aral Sea ( ; kk, Арал теңізі, Aral teñızı; uz, Орол денгизи, Orol dengizi; kaa, Арал теңизи, Aral teńizi; russian: Аральское море, Aral'skoye more) was an endorheic lake lying between Kazakh ...
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. 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 European countries where the birds do not regularly winter, as well as Algeria, Iraq, Palestine, Libya, Nepal, northeast Pakistan, and on the
Mariana Mariana may refer to: Literature * ''Mariana'' (Dickens novel), a 1940 novel by Monica Dickens * ''Mariana'' (poem), a poem by Alfred Tennyson, 1st Baron Tennyson * ''Mariana'' (Vaz novel), a 1997 novel by Katherine Vaz Music *"Mariana", a so ...
and Volcano Islands in the western Pacific. Vagrants on the spring migration have been sighted on Bear Island, Iceland and Svalbard, and in
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S ...
,
Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idah ...
and
Saskatchewan Saskatchewan ( ; ) is a province in western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on the south by the U.S. states of Montana and North ...
in North America. ''C. c. columbianus'' breeds in the coastal plains of Alaska and Canada, 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 is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...
; they often move inland – particularly to the rich feeding grounds in the Central Valley – and some cross the
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...
again and winter as far east as
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...
and south to
Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
and northern Mexico. The birds breeding along the
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...
coast migrate via Canada and the
Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five la ...
region to winter at the Atlantic coast of the United States, mainly from
Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; ...
to
North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia a ...
, but some move as far south as
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, a ...
. 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 the
Hawaiian Islands The Hawaiian Islands ( haw, Nā Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean, extending some from the island of Hawaii in the south to northernmost ...
,
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and Unincorporated ...
, and in England, Ireland, Japan, northeastern Siberia and Sweden.


Ecology and biology


Diet

In summer, their diet consists mainly of aquatic vegetation—e.g. mannagrass (''Glyceria''), ''
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 (''Elodea canadensis'') ...
'' pondweeds and
marine eelgrass ''Zostera'' is a small genus of widely distributed seagrasses, commonly called marine eelgrass, or simply seagrass or eelgrass, and also known as seaweed by some fishermen and recreational boaters including yachtsmen. The genus ''Zostera'' con ...
(''Zostera''), acquired by sticking the head underwater or upending while swimming; they also eat some grass growing on dry land. At other times of year, leftover
grain A grain is a small, hard, dry fruit ( caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legu ...
s and other
crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydropo ...
s such as
potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Un ...
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.


Natural predator

Healthy adult birds have few natural predators. The Arctic fox (''Vulpes lagopus'') may threaten breeding females and particular the eggs and hatchlings. Adults typically can stand their ground and displace foxes but occasionally the foxes are successful. Another surprisingly serious nest predator for tundra swans are
brown bear The brown bear (''Ursus arctos'') is a large bear species found across Eurasia and North America. In North America, the populations of brown bears are called grizzly bears, while the subspecies that inhabits the Kodiak Islands of Alaska is ...
s (''Ursus arctos''), which were apparently the primary cause of nesting failure in both the
Arctic National Wildlife Refuge The Arctic National Wildlife Refuge (ANWR or Arctic Refuge) is a national wildlife refuge in northeastern Alaska, United States on traditional Gwich'in lands. It consists of in the Alaska North Slope region. It is the largest national wildli ...
and Izembek National Wildlife Refuge. Other potential nest predators include red fox (''Vulpes vulpes''),
golden eagle The golden eagle (''Aquila chrysaetos'') is a bird of prey living in the Northern Hemisphere. It is the most widely distributed species of eagle. Like all eagles, it belongs to the family Accipitridae. They are one of the best-known birds ...
s (''Aquila chrysaetos''),
parasitic jaeger The parasitic jaeger (''Stercorarius parasiticus''), also known as the Arctic skua, Arctic jaeger or parasitic skua, is a seabird in the skua family Stercorariidae. It is a migratory species that breeds in Northern Scandinavia, Scotland, Iceland, ...
s (''Stercorarius parasiticus''), and glaucous gull (''Larus hyperboreus''). Brown bear, golden eagles and, rarely, gray wolves (''Canis lupus'') may on occasion succeed at capturing and killing an adult. Small or avian predators usually elicit either an aggressive response or the behavior of sitting tight on nests while larger mammals, perhaps more dangerous to adults, usually elicit the response of leading the cygnets into deep waters and standing still until they pass. 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 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 A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts ...
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, 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; although its population is in decline in northwestern Europe, for currently unexplained reasons. The European winter population was estimated at 16,000–17,000 about 1990, with about 20,000 birds wintering in east Asia. 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 crops to supplement their winter diet, as aquatic vegetation in their winter habitat dwindles due to
habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...
and
water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Wate ...
. 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 poachers and native
subsistence A subsistence economy is an economy directed to basic subsistence (the provision of food, clothing, shelter) rather than to the market. Henceforth, "subsistence" is understood as supporting oneself at a minimum level. Often, the subsistence econo ...
hunter-gatherers. Bewick's swan cannot be hunted legally, but almost half the birds studied contained lead shot in their body, indicating they were shot at by poachers.
Lead poisoning Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. The brain is the most sensitive. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, inferti ...
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
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natur ...
(IUCN) due to its large range and population. The proposed subspecies ''jankowskii'' was for some time placed on
CITES CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...
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 The Agreement on the Conservation of African-Eurasian Migratory Waterbirds, or African-Eurasian Waterbird Agreement (AEWA) is an independent international treaty developed under the auspices of the United Nations Environment Programme's Convent ...
'' (AEWA) applies. Toxic mining wastes in the Silver Valley,
Idaho Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and W ...
in the United States has been known to be responsible for the death of migrating tundra swans.


Gallery

bewicks.head.arp.jpg, Head of a Bewick's swan, ''C. c. bewickii'' Whooper1.jpg, Head of a whooper swan, ''C. cygnus'' tundra.swan.750pix.jpg, Whistling swan, ''C. c. columbianus'' Whistling Swan RWD3.jpg, Whistling swan, ''C. c. columbianus'' Trumpeter Swan - natures pics 2.jpg, Trumpeter swan, ''C. buccinator'' Cygnus bewickii 03.jpg, Bewick's swan feeding by upending Flock-of-tundra-swans.jpg, Flock of adult and young whistling swans Tundra swans (21523232431).jpg, Tundra swans alight at
Mattamuskeet National Wildlife Refuge The Mattamuskeet National Wildlife Refuge is a federally protected wildlife refuge located within Hyde County, North Carolina, United States. North Carolina's largest natural lake, Lake Mattamuskeet, is located entirely within the National Wildl ...
in North Carolina


References


Further reading

*


External links


RSPB Bewick's Swan Page




with Circumpolar Range map at bird-stamps.org * * * {{Authority control Tundra swan tundra swan Holarctic birds tundra swan Taxa named by George Ord