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 increasing, 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 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#.
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.
The Common Merganser can be found breeding year-round in central Asia and western China
, in northern Europe including France
, Scandinavia, the United Kingdom
, and in large areas of northern United States
and parts of southern Canada
. Summer breeding grounds include the majority of Scandinavia and Russia
, parts of central Asia including northern India
, northern regions of Kazakhstan
, and much of southern Canada. Wintering grounds expand the range further south to encompass most of the United States, other coastal regions of south-eastern Europe (e.g. Turkey
) and central Asia, and the eastern coast of China as well as Korea
. Population justification
The global population is estimated to number c.1,700,000-2,400,000 individuals (Wetlands International 2006), while national population estimates include: c.100-10,000 breeding pairs and c.50-1,000 wintering individuals in China; <c.100 breeding pairs and c.1,000-10,000 wintering individuals in Korea and c.1,000 wintering individuals in Japan (Brazil 2009).Trend justification
The overall population trend is increasing, although some populations may be stable and others have unknown trends (Wetlands International 2006). This species has undergone a small or statistically insignificant increase over the last 40 years in North America (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).EcologyBehaviour
Northern breeding populations of this species are fully migratory (Snow and Perrins 1998) although breeders in temperate regions are sedentary or only travel short distances (del Hoyo et al.
1992, Scott and Rose 1996). The species arrives on its breeding areas between March and May (Scott and Rose 1996), actually breeding as early as late-March (although often considerably later in more northerly regions) (Madge and Burn 1988). It breeds in solitary pairs or loose groups (del Hoyo et al.
1992) of up to 8-10 individuals (Flint et al.
1984) (especially on islands that provide suitable nesting sites in lacustrine or coastal locations) (Johnsgard 1978). The males gather to moult after mating, often undertaking considerable moult migrations to flock on key waters (Madge and Burn 1988). Females also undergo a post-breeding moult on the breeding grounds during which they become flightless for around 1 month (Johnsgard 1978). The main migration to wintering areas largely occurs from October through to December (Scott and Rose 1996), mass departures being linked to the freezing of breeding and moulting areas (Snow and Perrins 1998). Outside of the breeding season the species is typically found in small parties, with groups of up to 70 individuals feeding together on shoals of fish during the winter (Kear 2005b). Large flocks may also form on roosting waters (Madge and Burn 1988), the largest gatherings occurring during the autumn migration and winter months and numbering up to several thousands of individuals (Madge and Burn 1988) (1,000 to 10,000 on suitable waters) (Snow and Perrins 1998). On passage in the spring flocks are usually small however, breeding pairs remaining in flocks until they reach the breeding grounds (Snow and Perrins 1998). Habitat Breeding
The species breeds on large clear freshwater lakes (del Hoyo et al.
1992, Kear 2005b), pools (del Hoyo et al.
1992), the upper reaches of rivers (del Hoyo et al.
1992, Kear 2005b) and streams (Kear 2005b) in the boreal, montane (Kear 2005b) and temperate forest zones (Johnsgard 1978). It requires waters with a fairly high productivity of fish (Kear 2005b) surrounded by mature hard-wood trees with holes excavated by woodpeckers or natural cavities for nesting in (Kear 2005b). Non-breeding
The species winters on large unfrozen lakes, rivers, lagoons, brackish waters and marshes (Madge and Burn 1988, del Hoyo et al.
1992), generally avoiding highly saline waters (Madge and Burn 1988) although it may move to estuaries, coastal lagoons and sheltered sea coasts with waters less than 10 m deep in particularly harsh winters (Scott and Rose 1996). Diet
Its diet consists predominantly of fish (del Hoyo et al.
1992) less than 10 cm long (Kear 2005b), but may also include aquatic invertebrates (such as molluscs, crustaceans, worms, and adult and larval insects), amphibians, small mammals and birds (del Hoyo et al.
1992). Breeding site
The species nests in holes excavated by large woodpeckers or natural cavities in mature hardwood trees (del Hoyo et al.
1992, Kear 2005b) with entry holes more than 15 m above the ground (Kear 2005b). It shows a preference for cavities with openings c.12 cm wide and internal diameters of c.25 cm (Johnsgard 1978) in trees close to or up to 1 km away from water (Snow and Perrins 1998). When natural tree-nesting sites are not available (Johnsgard 1978) the species will use artificial nestboxes (del Hoyo et al.
1992, Kear 2005b) or may nest among tree roots in undercut banks, on cliff ledges (Kear 2005b), in rock clefts (Flint et al.
1984) or in dense scrub or loose boulders on islands (Kear 2005b). Sometimes several females may nest in the same tree (Madge and Burn 1988), especially on islands that provide suitable nesting sites in lacustrine or coastal locations (Johnsgard 1978). Management information
Artificial nestboxes commonly used are 85-100 cm high with openings 50-60 cm from the base (Johnsgard 1978).Threats
The species is subject to persecution by anglers and fish-farmers who accuse it of depleting fish stocks (del Hoyo et al.
1992), and it is occasionally drowned in freshwater fishing nets with mesh sizes greater than 5 cm (China) (Quan et al.
2002). The species is also threatened by the degradation of freshwater lakes through drainage and petroleum pollution in Russia (Grishanov 2006) and as a result of acid rain in North America (Kear 2005b). The species is susceptible to avian influenza so may be threatened by future outbreaks of the virus (Melville and Shortridge 2006). Utilisation
The species is hunted in North America (Kear 2005b) and Russia (Grishanov 2006) (although it is not a popular game bird) (Kear 2005b), and its eggs used to be (and possibly still are) harvested in Iceland (Gudmundsson 1979).
Brazil, M. 2009. Birds of East Asia: eastern China, Taiwan, Korea, Japan, eastern Russia. 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.
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.
Grishanov, D. 2006. Conservation problems of migratory waterfowl and shorebirds and their habitats in the Kaliningrad region of Russia. In: Boere, G.; Galbraith, C., Stroud, D. (ed.), Waterbirds around the world, pp. 356. The Stationary Office, Edinburgh, UK.
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.
Quan, R. C.; Wen, W.; Yang, X. 2002. Effects of human activities on migratory waterbirds at Lashihai Lake, China. Biological Conservation 108: 273-279.
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.
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.
IUCN Red List evaluators
Butchart, S., Symes, A.
BirdLife International (2015) Species factsheet: Mergus merganser. Downloaded from
http://www.birdlife.org on 04/05/2015.
Recommended citation for factsheets for more than one species: BirdLife International (2015) IUCN Red List for birds. Downloaded from
http://www.birdlife.org on 04/05/2015.
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
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