Thegreater scaup (Aythya marila), justscaup in Europe or, colloquially, "bluebill" in North America,[3] is a mid-sizeddiving duck, larger than the closely relatedlesser scaup andtufted duck. It spends the summer months breeding inIceland, east acrossScandinavia, northernRussia andSiberia,Alaska, and northernCanada. During the winter, itmigrates south to the coasts of Europe, eastern Asia, and North America.
Male greater scaup average slightly larger than the females but with much overlap;[4] they have a light blue-grey bill and yellow eyes. Their heads are dark, with a green to purple (depending on light angle) gloss; the breast is black, the belly white, the upperparts pale grey, and the wing shows a strong white stripe. The females are mostly brown, again with white on the wing. They have dull blue bills and a white patch on the face.
Greater scaup nest near water, typically on islands in northern lakes or on floating mats of vegetation. They begin breeding at age two, but start building nests in the first year. The drakes have a complexcourtship, which takes place on the return migration to the summer breeding grounds and concludes with the formation ofmonogamous pairs. Females lay aclutch of six to nine olive-buff-coloured eggs. The eggs hatch in 24 to 28 days. Thedown-covered ducklings are able to follow their mother in her search for food immediately after hatching.
Greater scaup eat aquaticmolluscs, plants, and insects, which they obtain by diving underwater to depths of 0.5–6 m, exceptionally 10 m.[4] They form large groups, called "rafts", that can number in the thousands. Their main threat is human development, although they are also preyed upon by owls, skunks, raccoons, foxes, coyotes, and humans. Greater scaup populations have been declining since the 1980s; however, they are still listed as a species of least concern on theIUCN Red List.[2]
The genus nameAythya is derived from theAncient Greekαἴθυιᾰ (aithuia) which refers to a seabird mentioned byAristotle and others and is thought to refer to a seaduck or other seabird. The species namemarila is from the Greek word for charcoal embers or coal dust.[9]
Twosubspecies of Greater scaup are currently accepted. The nominateA. m. marila is found from northern Europe to east Siberia, west of theLena River. The birds in North America are treated as a separate subspeciesA. m. nearctica,[10] and are distinguishable from those in Eurasia by a typically higher forehead, and the male having stronger vermiculations on the mantle andscapulars. Additionally, there is less extensive white on the primary feathers thanA. m. marila.[11] Greater scaup in far eastern Asia (east of the Lena River towards the Bering Sea) are intermediate between the two subspecies and sometimes lumped with either race, or a distinct subspeciesA. m. mariloides, though the latter name is invalid, as it was first used to describe the lesser scaupA. affinis.[12] Based on size differences, aPleistocenepaleosubspecies,Aythya marila asphaltica, has also been described by Serebrovskij in 1941 fromfossils recovered atBinagady, Azerbaijan. Aphylogenetic analysis of the diving ducks, examining the skeletal anatomy and skin, found that the greater and lesser scaups are each other's closest relatives, with thetufted duck as the next closest relative of the pair.[13]
A. m. marila female, Laxá River, Northeastern Iceland
A. m. marila male, Northumberland, UK
The greater scaup's English name, first attested as 'Scaup Duck' in 1678, most likely comes from "scaup" or "scalp", aScottish andNorthern English word for a shellfish bed, where the birds typically feed in winter.[14][15] but could also be from the duck'smating call: "scaup scaup".[citation needed]
The adult greater scaup is 39–56 cm (15–22 in) long with a 71–84 cm (28–33 in) wingspan and a weight of 726–1,360 g (1.601–2.998 lb). It has a light blue bill with a small blacknail on the tip, yellow eyes, and is 20% heavier and 10% longer than the closely related lesser scaup.[16] The male has a dark head with a green to purple sheen, a black breast, a light back, a black tail, and a white underside. The drake or male is larger and has a more rounded head than the female. The drake's belly and flanks are a bright white. Its neck, breast, and tail feathers are glossy black, while its lower flanks arevermiculated grey. The upper wing has a white stripe starting as thespeculum and extending along the flight feathers to the wingtip. Legs and feet of both sexes are grey.
The adult female has a brown body and head, with white wing markings similar to those of the male but slightly duller. It has a white band and brown oval shaped patches at the base of the bill, which is a slightly duller shade of blue than the drake's.[17] Juvenile greater scaup look similar to adult females. The drake'seclipse plumage looks similar to its breeding plumage, except the pale parts of the plumage are a buffy grey.[18]
Distinguishing greater from lesser scaups can be difficult in the field. The head of the greater tends to be more rounded, and the white wing stripe is more extensive. The bill is also tends to be larger and wider, with a slightly larger black nail at the tip. The North American subspeciesA. m. nearctica typically has a higher forehead and reduced white on the wings, intermediate between the EuropeanA. m. marila and Lesser Scaup.[16]
The greater scaup has a circumpolar distribution, breeding within the Arctic Circle both in the Old World (thePalearctic) and in North America (theNearctic). It spends the summer months inIceland, east acrossScandinavia, northernRussia andSiberia,Alaska, and northernCanada. It is mostly migratory, but small numbers are present in Iceland and theAleutian Islands year round.[19] The summer habitat is marshy lowlandtundra and islands in fresh water lakes. In the autumn, greater scaup populations start their migration south for the winter. They winter along the Pacific and Atlantic coasts of North America, the coasts of northwest Europe, theCaspian Sea, theBlack Sea, the coast of Japan,Yellow Sea andEast China Sea.[20] During the winter months, they are found in coastal bays,estuaries, and sometimes inland lakes,[21] such as the lakes ofCentral Europe and theGreat Lakes.[20]
In Europe, the greater scaup breeds in Iceland, the northern coasts of theScandinavian Peninsula, including much of the northern parts of theBaltic Sea, the higher mountains of Scandinavia and the areas close to theArctic Sea in Russia. It has also bred sporadically in northernScotland.[4] These birds spend the winters in theBritish Isles, western Norway, the southern tip of Sweden, the coast fromBrittany to Poland, including all of Denmark, the Alps, the easternAdriatic Sea, the northern and western Black sea and the southwestern Caspian Sea.[22][23]
Greater scaup breed in the tundra and theboreal forest; it is estimated that 75% of the North American population breed in Alaska. They typically nest on islands in large northern lakes. Greater scaup begin breeding when they are two years old, although they may start nesting at age one. Drake greater scaup have a soft, quick whistle they use to attract the attention of hens during courtship, which takes place from late winter to early spring, on the way back to their northern breeding grounds. Female greater scaup have a single pitch, a raspy "arrr-arrr-arrr-arrr-arrr" call note.[24] The courtship is complex and results in the formation of monogamous pairs.[25]
Pairs nest in close proximity to each other in large colonies, usually near water, on an island or shoreline, or on a raft of floating vegetation. The nest consists of a shallow depression made by the female and lined with her down.[16] After the female lays the eggs, the drake abandons the female[25] and goes with other drakes to a large, isolated lake to moult. These lakes can be close to the breeding grounds, or distant, with birds performing amoult migration of up to several hundred km, such as from northern Scandinavia to theIJsselmeer in the Netherlands.[4] The lakes chosen are used yearly by the same ducks. The optimal moulting lake is fairly shallow and has an abundance of food sources and cover.[26]
The female lays six to nine olive-buff-coloured eggs,[27] which sheincubates for 24–28 days.[28] A larger clutch could indicatebrood parasitism by other greater scaups or even ducks of other species.[29] The newly hatched ducklings are covered with down and are soon able to walk, swim, and feed themselves; however, they are not able to fly until 40–45 days after hatching.[20][25] The vulnerable small ducklings follow their mother, who protects them from predators.[25]
The greater scaup dive to obtain food, which they eat on the surface.[16] They mainly eatmolluscs, aquatic plants, and aquatic insects.[24] During the summer months, the greater scaup will eat small aquaticcrustaceans.[16] There is a report of four greater scaups in April near Chicago swallowing hibernatingleopard frogs (a species with a body length about 5 centimetres, or 2.0 in), which they dredged out of a roadside freshwater pond.[30] In freshwaterecosystems, the greater scaup will eat seeds, leaves, stems and roots, along with sedges, pondweeds,muskgrass, andAmerican eelgrass.[17] Owing to the greater scaup's webbed feet and weight, it can dive up to 6–10 metres (20–30 ft) and stay submerged for up to a minute.[31] In the past, they also often fed in winter in huge flocks on spent grain pumped offshore from distilleries (notably in theFirth of Forth in Scotland), but with modern pollution control, this food source is no longer available.[4][32]
Common predators of the greater scaup areowls,foxes,skunks,raccoons,coyotes, and humans.[33] Greater scaup often become entangled in fishing nets, and large numbers of them drown in this way each year. Greater scaup can catchavian influenza, so future outbreaks have the potential to threaten their populations.[19]
Although the greater scaup faces numerous threats, the most significant challenge to their survival is habitat degradation caused by a mix of human development and runoff.[34] Greater scaup, when moulting and during the winter, are threatened by escalated levels of organochloride contaminants. Oil and sewage pollution also threaten this duck. Since 80% of the greater scaup population winters in the urbanised part of theAtlantic Flyway, these ducks are subject to high levels of organic contaminants, along with increased levels of heavy metals in foods and habitat.[21]
A joint group of American and Canadian scientists researching scaup migration across the Great Lakes found that 100% of female greater scaup and 77% of female lesser scaup had escalated levels ofselenium in their bodies. Selenium is asemimetallictrace element that occurs naturally in some soils; minute amounts of it are necessary for animal life. However, excessive selenium can cause reproductive harm and is highly toxic. On their migration across the Great Lakes, greater scaups are at risk of ingesting selenium by eating the invasivezebra mussels, which can render the female scaupinfertile.[3] This sterilization is causing the population to decrease.
In a study of 107 scaup, they all had traces ofiron,zinc,manganese,copper,lead,cadmium,cobalt andnickel in their tissue samples with varying concentrations of metals in different types of tissues. The kidneys had the highest levels of cadmium, the liver had the highest levels of copper and manganese, the liver and the stomach had the highest levels of zinc, and the lungs and liver had the highest levels of iron.[35] There was no difference in concentrations when comparing sexes.
Greater scaup are rated as a species of least concern by the IUCN Redlist.[2] During aerial population surveys greater and lesser scaup are counted together, because they look almost identical from the air. It was estimated that the greater scaup made up about 11% of the continental scaup population. Since the 1980s, scaup populations have been steadily decreasing. Some of the primary factors contributing to this decline arehabitat loss, contaminants, changes in breeding habitat, and a lower female survival rate. The 2010 American scaup population survey was 4.2 million scaup,[36] however, the worldwide greater scaup population survey estimated 1,200,000 to 1,400,000 mature greater scaup.[19] Along with the aerial population surveys, there is aringing programme for the greater scaup. Metal leg bands are placed on them, so that if the scaup is killed by a hunter or if it is captured by another ringing group, the number on the band can be reported to biologists and wildlife organisations. These ringing programmes yield valuable data about migration patterns, harvest rates, and survival rates.[37]
Greater scaup decoys, male on the left and female on the right. Each is attached to a lead weight.
Greater scaup are a populargame bird in North America and Europe.[38] They are hunted in Denmark, Germany, Greece, France, the United Kingdom, and Ireland,[38] and in Iran for both sport and commercial reasons.[20] Greater scaup are hunted withshotguns because they must be shot on the fly, a challenging task, as they can fly at up to 121 km/h (75 mph). Greater scaup are hunted from shorelines and in open waterhunting blinds orlayout boats, low-profilekayak-like boats that hunters lie inside. Hunters frequently usedecoys to attract the birds, often arranged to simulate a raft of greater scaup and featuring an open area to attract the birds to land.[39]
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^ab"Bluebills". Minnesota Department of Natural Resources. Archived fromthe original on 20 December 2013. Retrieved3 November 2011.
^abcdeCramp, Stanley, ed. (1977). "Aythya marila Scaup".Handbook of the Birds of Europe the Middle East and North Africa. The Birds of the Western Palearctic. Vol. I: Ostrich to Ducks. Oxford: Oxford University Press. pp. 586–593.ISBN978-0-19-857358-6.
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^Ullman, Magnus (1992).Fåglar i Europa [Birds in Europe] (in Swedish). Wahlström & Widstrand. p. 102.ISBN978-91-46-17633-6.
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^Campbell, L. H. (1986). "Tufted Duck". In Lack, Peter (ed.).The Atlas of Wintering Birds in Britain and Ireland. London, UK: T & AD Poyser. p. 112.ISBN978-1-4081-3828-1.
^"Greater Scaup". National Biological Information Infrastructure. Archived fromthe original on 9 December 2011. Retrieved8 November 2011.
^Szefer, Piotr; Falandysz, Jerzy (1987). "Trace metals in the soft tissues of scaup ducks (Aythya marila L.) wintering in Gdańsk bay, Baltic sea".Science of the Total Environment.65:203–213.Bibcode:1987ScTEn..65..203S.doi:10.1016/0048-9697(87)90173-2.
^"Waterfowl Hunting Management in North America".Scaup Population Estimates. U.S. Fish and Wildlife Service in collaboration with flyway and state waterfowl managers. 29 June 2010. Archived fromthe original on 16 October 2011. Retrieved4 November 2011.
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