LC
Goosander Mergus merganser



Justification

Justification of Red List Category
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 is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds 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.

Population justification
The global population is estimated to number c.1,700,000-2,400,000 individuals (Wetlands International 2015). The European population is estimated at 66,800-103,000 pairs, which equates to 134,000-206,000 mature individuals (BirdLife International 2015).

Trend justification
The overall population trend is not known, although some populations are increasing, some decreasing, some stable and others have unknown trends (Wetlands International 2015). In Europe the population size is estimated to be stable (BirdLife International 2015). 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).

Distribution and population

This species can be found breeding year-round in central Asia and western China, in northern Europe including France, Germany, Scandinavia, the United Kingdom and Iceland, 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, Mongolia and Japan, 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 Greece) and central Asia, and the eastern coast of China as well as Korea and Japan.

Ecology

Behaviour 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 2005). 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, with 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 2005), pools (del Hoyo et al. 1992), the upper reaches of rivers (del Hoyo et al. 1992, Kear 2005) and streams (Kear 2005) in the boreal, montane (Kear 2005) and temperate forest zones (Johnsgard 1978). It requires waters with a fairly high productivity of fish (Kear 2005) surrounded by mature hard-wood trees with holes excavated by woodpeckers or natural cavities for nesting in (Kear 2005). 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 2005), 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 2005) with entry holes more than 15 m above the ground (Kear 2005). 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 2005) or may nest among tree roots in undercut banks, on cliff ledges (Kear 2005), in rock clefts (Flint et al. 1984) or in dense scrub or loose boulders on islands (Kear 2005). 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 perceive it as a competitor and accuse it of depleting their fish stocks (del Hoyo et al. 1992). Eradication efforts may lead to long-term depression of Goosander populations (with little improvement in fish survival rates) (Pearce et al. 2015). The species suffers occasional entrapment in freshwater fishing nets with mesh sizes greater than 5 cm, with records of bycatch from China (Quan et al. 2002). The species is also at risk from degradation of freshwater lakes resulting from drainage and petroleum pollution in Russia (Grishanov 2006) and acid rain in North America (Kear 2005). The species is susceptible to avian influenza and is at risk from future outbreaks of the virus (Melville and Shortridge 2006). Hunting occurs in North America (Kear 2005) and Russia (Grishanov 2006), but the Goosander is not a popular game bird (Kear 2005). Its eggs used to be, and possibly still are, harvested in Iceland (Gudmundsson 1979). Present harvesting levels are sufficiently low not to be driving declines.

Conservation actions

Conservation Actions Underway
CMS Appendix II. EU Birds Directive Annex II. There are currently no known direct conservation measures for this species within its European range.

Conservation Actions Proposed
The following information refers to the species's European range only: The erection of nest boxes may encourage the use of local areas by this species (Kear 2005). Future research to inform the conservation and management of this species should include investigations into its breeding requirements, winter habitats and population size (Mallory and Metz 1999). Strict legislation on petroleum drilling and transport should be enforced and important areas protected from drainage and other habitat modifications. Research into the impact this species has on fish stocks and ways to minimise conflict should be established.

Acknowledgements

Text account compilers
Martin, R., Stuart, A., Bennett, S., Butchart, S., Calvert, R., Ekstrom, J., Fjagesund, T., Ashpole, J, Hermes, C., Malpas, L.

Contributors
Pihl, S.


Recommended citation
BirdLife International (2019) Species factsheet: Mergus merganser. Downloaded from http://www.birdlife.org on 17/08/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/08/2019.