This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Although the population may be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Distribution and population
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: http://www.aerc.eu/DOCS/Bird_taxa_of _the_WP15.xls.
AOU. 1998. Check-list of North American birds. American Ornithologists' Union, Washington, D.C.
Cramp, S.; Perrins, C. M. 1977-1994. Handbook of the birds of Europe, the Middle East and Africa. The birds of the western Palearctic. Oxford University Press, Oxford.
Sibley, C. G.; Monroe, B. L. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, USA.
Stotz, D. F.; Fitzpatrick, J. W.; Parker, T. A.; Moskovits, D. K. 1996. Neotropical birds: ecology and conservation. University of Chicago Press, Chicago.
Summer breeding grounds of the Greater Scaup range across the northern limits of Europe (including Iceland
) and Asia, through the Aleutian Islands (year-round breeding) to Alaska (USA
), and across to the Atlantic coast of Canada
(del Hoyo et al
. 1992). It winters further south, reaching California, the great lakes and northern Florida in North America, the Adriatic Sea and northern Black Sea in Europe, the western Caspian Sea, and on the Pacific coast of Asia as far as south-east China
(del Hoyo et al
. 1992). Population justification
The global population is estimated to number c.1,200,000-1,400,000 individuals (Wetlands International 2006), while national population sizes have been estimated at c.50-1,000 individuals on migration and c.50-1,000 wintering individuals in Taiwan and c.1,000 wintering individuals in Korea (Brazil 2009).Trend justification
The overall population trend is decreasing, although some populations may be stable or increasing and others have unknown trends (Wetlands International 2006). This species has underwent a significant population increase between 1974 and 2011 in North America (Zimpfer 2011, T. McCoy in litt.
This species is fully migratory (del Hoyo et al
. It breeds in the high Arctic from late-May or early-June (depending on the timing of the Arctic thaw) (Kear 2005b)
in single pairs or loose groups (del Hoyo et al
, often with colonies of nesting gulls or terns (Kear 2005b)
although it is not itself a colonial species (Snow and Perrins 1998)
. Males undergo short post-breeding moult migrations (Madge and Burn 1988, Scott and Rose 1996)
, often gathering in small or large flocks (up to 4,000 in Iceland) (Scott and Rose 1996)
while females are incubating (Madge and Burn 1988)
. Females usually moult on the breeding grounds (Madge and Burn 1988, Scott and Rose 1996)
, although large concentrations (500-1,000 individuals) of moulting females have been recorded away from breeding areas (Scott and Rose 1996)
. During the moulting period the species is flightless for a period of c.3-4 weeks (Scott and Rose 1996)
. The autumn migration begins after the moulting period in mid-August (Scott and Rose 1996)
, with males tending to remain much further north than females or immatures (del Hoyo et al
leading to some sexual segregation during the winter ( Madge and Burn 1988)
. The species is highly gregarious outside of the breeding season (Kear 2005b)
and is commonly observed in small or large flocks ( Madge and Burn 1988)
sometimes of several thousand individuals (Scott and Rose 1996)
. The return spring migration generally begins in late-February (Scott and Rose 1996)
although flocks of non-breeders may remain in the south, often in winter quarters, during the breeding season (Madge and Burn 1988)
. Habitat Breeding
The species breeds in tundra (Kear 2005b)
, wooded tundra (Scott and Rose 1996)
and moorland regions (Kear 2005b)
in the high Arctic (del Hoyo et al
, occupying small, shallow (del Hoyo et al
, freshwater lakes, pools and rivers (Kear 2005b)
with grassy shorelines and high densities of invertebrate life (Johnsgard 1978)
. It shows a preference for water less than 6 m deep (usually 2 m) for diving (Kear 2005b)
The species winters on shallow coastal waters (del Hoyo et al
. 1992, Kear 2005b)
less than 10 m deep (Scott and Rose 1996)
(especially in the vicinity of sewage outlets) (del Hoyo et al
, as well as sheltered bays (del Hoyo et al
, estuaries (del Hoyo et al
. 1992, Kear 2005b)
and brackish coastal lagoons (del Hoyo et al
. It is also found inland on large lakes (Johnsgard 1978, del Hoyo et al
. 1992, Kear 2005b)
and reservoirs during this season (Madge and Burn 1988)
The species is omnivorous (Kear 2005b)
, its diet consisting predominantly of molluscs (e.g. mussels [Kear 2005b] Mytilus
spp. [del Hoyo et al
, cockles Cardium
spp. and clams Macoma
spp. in coastal habitats, and Hydrobia
spp. in brackish habitats [Kear 2005b]
) especially during the winter (Johnsgard 1978)
, as well as insects (del Hoyo et al
, aquatic insect larvae (Johnsgard 1978)
, crustaceans (del Hoyo et al
(e.g. amphipods [Johnsgard 1978]
), worms, small fish (del Hoyo et al
, and the roots, seeds and vegetative parts of aquatic plants such as sedges (del Hoyo et al
. 1992) (Kear 2005b)
and water weeds (Kear 2005b)
The nest is a shallow depression close to water (Madge and Burn 1988)
on the ground (del Hoyo et al
, either in thick vegetation (del Hoyo et al
. 1992) (Kear 2005b)
, in cracks in rocks, under woody shrubs or under perennial herbaceous vegetation less than 50 cm high (Iceland) (Johnsgard 1978)
. The species is not colonial but it will sometimes nest among gulls and terns (Kear 2005b)
, with neighbouring nests being placed as close as 1 m in some areas (Snow and Perrins 1998)
In Scotland, UK the introduction of a sewage treatment scheme in the Firth of Forth (a large marine bay) resulted in a considerable reduction in the abundance of the species, with feeding flocks only remaining at outfalls where sewage continued to be discharged in large quantities (Campbell 1984)
. It was unclear whether the changes in the species's distribution were due to reductions in the number of food items borne in the sewage or to reductions in aquatic invertebrate abundance as a result of the new treatment system (Campbell 1984)
The species is susceptible to oil pollution (Kirby et al
. 1993, Kear 2005b)
when moulting and in winter and may be threatened by high levels of organochloride contaminants (Kear 2005b)
. Its habit of congregating around coastal sewage outlets in the winter also puts it at risk from other pollution types (del Hoyo et al
and large numbers often drown due to entanglement in fishing nets (Kirby et al
. The species is threatened by hunting for sport in North America (Schmidt 2006, Blohm et al.
, and suffers from disturbance from hunting (Evans and Day 2002)
. It is also susceptible to avian influenza, so may be threatened by future outbreaks of the virus (Melville and Shortridge 2006)
The species is hunted legally for sport in seven countries of the European Union (Kear 2005b)
(e.g. Denmark [Bregnballe et al
), and is hunted for commercial and recreational purposes in Iran (Balmaki and Barati 2006)
Related state of the world's birds case studies
Johnsgard, P. A. 1978. Ducks, geese and swans of the World. University of Nebraska Press, Lincoln and London.
Campbell, L. H. 1984. The impact of changes in sewage treatment on seaducks wintering in the Firth of Forth, Scotland. Biological Conservation 28: 173-180.
Madge, S.; Burn, H. 1988. Wildfowl. Christopher Helm, London.
del Hoyo, J.; Elliot, A.; Sargatal, J. 1992. Handbook of the Birds of the World, vol. 1: Ostrich to Ducks. Lynx Edicions, Barcelona, Spain.
Kirby, J.; Evans, R.; Fox, A. D. 1993. Wintering seaducks in Britain and Ireland: Populations, threats, conservation and research priorities. Aquatic Conservation: Marine and Freshwater Ecosystems 3(2): 105-137.
Scott, D. A.; Rose, P. M. 1996. Atlas of Anatidae populations in Africa and western Eurasia. Wetlands International, Wageningen, Netherlands.
Snow, D. W.; Perrins, C. M. 1998. The Birds of the Western Palearctic vol. 1: Non-Passerines. Oxford University Press, Oxford.
Kear, J. 2005. Ducks, geese and swans volume 2: species accounts (Cairina to Mergus). Oxford University Press, Oxford, U.K.
Balmaki, B.; Barati, A. 2006. Harvesting status of migratory waterfowl in northern Iran: a case study from Gilan Province. In: Boere, G.; Galbraith, C., Stroud, D. (ed.), Waterbirds around the world, pp. 868-869. The Stationary Office, Edinburgh, UK.
Blohm, R. J.; Sharp, D. E.; Padding, P. I.; Kokel, R. W.; Richkus, K. D. 2006. Integrated waterfowl management in North America. In: Boere, G.; Galbraith, C.; Stroud, D. (ed.), Waterbirds around the world, pp. 199-203. The Stationary Office, Edinburgh, UK.
Bregnballe, T.; Noer, H.; Christensen, T. K.; Clausen, P.; Asferg, T.; Fox, A. D.; Delany, S. 2006. Sustainable hunting of migratory waterbirds: the Danish approach. In: Boere, G.; Galbraith, C., Stroud, D. (ed.), Waterbirds around the world, pp. 854-860. The Stationary Office, Edinburgh, UK.
Melville, D. S.; Shortridge, K. F. 2006. Migratory waterbirds and avian influenza in the East Asian-Australasian Flyway with particular reference to the 2003-2004 H5N1 outbreak. In: Boere, G.; Galbraith, C., Stroud, D. (ed.), Waterbirds around the world, pp. 432-438. The Stationary Office, Edinburgh, UK.
Schmidt, P. R. 2006. Flyway conservation in North America. Workshop Introduction. In: Boere, G.; Galbraith, C., Stroud, D. (ed.), Waterbirds around the world, pp. 197-198. The Stationary Office, Edinburgh, UK.
Evans, D. M.; Day, K. R. 2002. Hunting disturbance on a large shallow lake: the effectiveness of waterfowl refuges. Ibis 144(1): 2-8.
Further web sources of information
Detailed species account from Birds in Europe: population estimates, trends and conservation status (BirdLife International 2004)
Hear sounds for this species from xeno-canto, the community database of shared bird sounds from around the world.
View photos and videos, and hear sounds of this species from the Internet Bird Collection
Text account compilers
Butchart, S., Calvert, R., Derhé, M., Ekstrom, J., Malpas, L.
Barclay, J., Bianki, V., Burfield, I., DeVink, J., Ellermaa, M., Kharitonova, I., Kharitonov, S., Kontiokorpi, J., Lehikoinen, A., Lehikoinen, E., McCoy, T., Szymanski, M.
IUCN Red List evaluators
Butchart, S., Symes, A.
BirdLife International (2013) Species factsheet: Aythya marila. Downloaded from
http://www.birdlife.org on 25/05/2013.
Recommended citation for factsheets for more than one species: BirdLife International (2013) IUCN Red List for birds. Downloaded from
http://www.birdlife.org on 25/05/2013.
This information is based upon, and updates, the information published in BirdLife International (2000)
Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004)
Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.
To provide new information to update this factsheet or to correct any errors, please email BirdLife
To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.
Additional resources for this species