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Red-breasted Merganser Mergus serrator
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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). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very 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.

Taxonomic source(s)
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: # _the_WP15.xls#.
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.
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Distribution and population
The red-breasted Merganser breeds in most of the northern North America, south to the Great Lakes, in Greenland (to Denmark), Iceland, and much of northern Eurasia south to the United Kingdom, parts of Eastern Europe, north-east China and northern Japan. Its wintering grounds expand its range to include the Atlantic and Pacific coasts of North America, areas of central Europe and the Mediterranean basement, the Black Sea, the southern Caspian Sea, the southern coast of Iran and Pakistan, the eastern coast of China, and the coasts of Korea and Japan1.

Population justification
The global population is estimated to number c.510,000-610,000 individuals (Wetlands International 2006). National population estimates include: c.100-10,000 breeding pairs and c.50-1,000 wintering individuals in China; <c.50 individuals on migration and <c.50 wintering individuals in Taiwan; c.50-10,000 wintering individuals in Korea and c.100,000-1 million breeding pairs and c.1,000-10,000 wintering individuals in Russia (Brazil 2009).

Trend justification
The overall population trend is stable, although some populations have unknown trends (Wetlands International 2006). This species has had stable population trends over the last 40 years in North America (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).

Behaviour This species is fully migratory (Madge and Burn 1988, del Hoyo et al. 1992) although in temperate regions it only undertakes short distance movements to nearby coasts (Scott and Rose 1996) or remains close to its breeding waters throughout the year (Madge and Burn 1988). It breeds from April or May (later in northern populations) (Kear 2005b) in single pairs or colonies (del Hoyo et al. 1992) on islands or small islets, adults often assembling in groups on beaches when not at the nest (even when nesting solitarily) (Kear 2005b). Males leave the breeding grounds in June to moult in small groups along the coast (Scott and Rose 1996), often considerable distances from the breeding areas (Snow and Perrins 1998) (although there is no evidence for any major migrations to common moulting sites) (Johnsgard 1978). The autumn migration begins in September (Scott and Rose 1996) and the species returns from the wintering grounds as early as February (Scott and Rose 1996). It is gregarious during the winter and on migration (Kear 2005b), flocks of up to a hundred or more occurring in suitable sites during the autumn (although it travels in much smaller flocks during the spring) (Snow and Perrins 1998). Habitat Breeding The species breeds along the wooded shorelines (Kear 2005b) of deep lakes (del Hoyo et al. 1992), small rivers and streams (del Hoyo et al. 1992) with moderate currents (Snow and Perrins 1998) in the tundra, boreal and temperate forest zones (Snow and Perrins 1998, Kear 2005b), as well as on more saline waters such as sheltered shallow bays, inlets, straits or estuaries with sandy rather than muddy substrates (Snow and Perrins 1998). It shows a preference for narrow channels rather than open expanses of water, with islands or islets and spits, projecting rocks or grassy banks (Snow and Perrins 1998). Non-breeding The majority of the species winters at sea (del Hoyo et al. 1992), frequenting both inshore and offshore waters, estuaries, bays and brackish lagoons (del Hoyo et al. 1992) but showing a preference for clear, shallow waters not affected by heavy wave action (Johnsgard 1978). It will also utilise large freshwater lakes on passage (Madge and Burn 1988). Diet Its diet consists predominantly of small, shoaling marine or freshwater fish (del Hoyo et al. 1992), as well as small amounts of plant material (del Hoyo et al. 1992) and aquatic invertebrates (del Hoyo et al. 1992) such as crustaceans (e.g. shrimps and crayfish) (Johnsgard 1978), worms and insects (Kear 2005b). Breeding site The nest is constructed within 25 m of water (Kear 2005b) in a variety of locations such as natural cavities on the ground (Johnsgard 1978, del Hoyo et al. 1992, Kear 2005b) , burrows (del Hoyo et al. 1992, Kear 2005b), under boulders (Madge and Burn 1988), amongst tree or scrub roots (Snow and Perrins 1998), in tree cavities, artificial nestboxes (Madge and Burn 1988), amongst reeds or on floating reed mats (Flint et al. 1984). Where tree cavities or artificial nestboxes are utilised, the species shows a preference for those with entrances c.10 cm in diameter and with internal diameters of 30-40 cm (Johnsgard 1978). Management information The breeding density of this species increased on islands in the outer archipelago of south-west Finland as a result of feral American mink Neovison vison removal (Nordstrom et al. 2002). The species will also nest in artificial nestboxes with entrances c.10 cm in diameter and with internal diameters of 30-40 cm (Johnsgard 1978).

The species is subject to persecution and may be shot (Kear 2005b) by anglers and fish-farmers who accuse it of depleting fish stocks (del Hoyo et al. 1992, Kear 2005b). It is also threatened by accidental entanglement and drowning in fishing nets (Kear 2005b). Alterations to its breeding habitats by dam construction and deforestation, and habitat degradation from water pollution are other major threats to the species (del Hoyo et al. 1992). It is also susceptible to avian influenza so may the threatened by future outbreaks of the virus (Melville and Shortridge 2006). Utilisation The species is hunted in North America (Kear 2005b) and Denmark (Bregnballe et al. 2006), although it may not be a popular game species (Kear 2005b). The eggs of the species also used to be (and possibly still are) harvested in Iceland (Gudmundsson 1979).

Related state of the world's birds case studies

Brazil, M. 2009. Birds of East Asia: eastern China, Taiwan, Korea, Japan, eastern Russia. Christopher Helm, London.

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.

del Hoyo, J.; Elliot, A.; Sargatal, J. 1992. Handbook of the Birds of the World, vol. 1: Ostrich to Ducks. Lynx Edicions, Barcelona, Spain.

Delany, S.; Scott, D. 2006. Waterbird population estimates. Wetlands International, Wageningen, The Netherlands.

Flint, V. E.; Boehme, R. L.; Kostin, Y. V.; Kuznetsov, A. A. 1984. A field guide to birds of the USSR. Princeton University Press, Princeton, New Jersey.

Gudmundsson, F. 1979. The past status and exploitation of the Myvatn waterfowl populations. Oikos 32((1-2)): 232-249.

Johnsgard, P. A. 1978. Ducks, geese and swans of the World. University of Nebraska Press, Lincoln and London.

Kear, J. 2005. Ducks, geese and swans volume 2: species accounts (Cairina to Mergus). Oxford University Press, Oxford, U.K.

Madge, S.; Burn, H. 1988. Wildfowl. Christopher Helm, London.

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.

Nordström, M.; Högmander, J.; Nummelin, J.; Laine, J.; Laanetu, N.; Korpimäki, E. 2002. Variable responses of waterfowl breeding populations to long-term removal of introduced American mink. Ecography 25: 385-394.

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.

Vahatalo, A. V.; Rainio, K.; Lehikoinen, A.; Lehikoinen, E. 2004. Spring arrival of birds depends on the North Atlantic Oscillation. Journal of Avian Biology 35: 210-216.

Further web sources of information
Detailed species account from Birds in Europe: population estimates trends and conservation status (BirdLife International 2004)

Detailed species account from Birds in Europe: population estimates, trends and conservation status (BirdLife International 2004)

Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Ekstrom, J., Butchart, S., Malpas, L., Calvert, R.

Pihl, S.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2016) Species factsheet: Mergus serrator. Downloaded from on 21/10/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from on 21/10/2016.

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

ARKive species - Red-breasted merganser (Mergus serrator) 0

Key facts
Current IUCN Red List category Least Concern
Family Anatidae (Ducks, Geese, Swans)
Species name author Linnaeus, 1758
Population size mature individuals
Population trend Stable
Distribution size (breeding/resident) 4,090,000 km2
Country endemic? No
Links to further information
- Additional Information on this species
- 2015 European Red List assessment