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). Despite the fact that the population trend appears to 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.
The global population has been estimated at 600,000-1,000,000 individuals (Delany and Scott 2006), probably including c.400,000-700,000 mature individuals, on the basis that they account for around 2/3 of the population.
There is some limited anecdotal evidence of a decline in the population during the past four decades (N. Moores in litt. 2012); however, further data are needed in order to estimate the rate of decline.
Behaviour This species is highly migratory (Madge and Burn 1988, del Hoyo et al. 1992) and breeds from mid-May onwards (Madge and Burn 1988) in solitary pairs or loose groups (del Hoyo et al. 1992, Kear 2005), occasionally nesting in association with gull or tern colonies (Kear 2005). Non-breeding birds spend the breeding season in flocks on open water (Flint et al. 1984). After breeding (from June onwards [Scott and Rose 1996]) the adults migrate to moulting sites (males travelling and moulting before the females) (Madge and Burn 1988), where they become flightless for 3-4 weeks (Scott and Rose 1996). When moulting and overwintering the species is highly sociable and can occur in large flocks (Madge and Burn 1988, Scott and Rose 1996) of several thousands of individuals (Scott and Rose 1996), although it is more common in small scattered groups of c.100 individuals (Snow and Perrins 1998). The species mainly forages by diving and may feed at depths of 30-40 m during the winter (del Hoyo et al. 1992). Habitat Breeding The species breeds on wooded coastlines (Johnsgard 1978, Kear 2005), small freshwater lakes (del Hoyo et al. 1992, Snow and Perrins 1998, Kear 2005), pools and rivers (Snow and Perrins 1998) in northern coniferous forests (Johnsgard 1978, del Hoyo et al. 1992, Snow and Perrins 1998, Kear 2005), wooded Arctic tundra (del Hoyo et al. 1992, Snow and Perrins 1998) and alpine zones (Snow and Perrins 1998, Kear 2005), especially where there are boulder-covered or small rocky islands available for nesting with extensive herbaceous vegetation, shrubs and low trees (Johnsgard 1978, Kear 2005). Non-breeding The majority winter at sea on shallow inshore coastal waters (Madge and Burn 1988, del Hoyo et al. 1992), especially in estuaries or inlets where there are large mussel-beds (Snow and Perrins 1998). The species may also occur on freshwater lakes and estuaries during migration (Madge and Burn 1988, Kear 2005). Diet Its diet consists predominantly of molluscs, as well as crustaceans, worms, echinoderms (del Hoyo et al. 1992), amphipods, isopods (Kear 2005), small fish, and (in freshwater habitats) adult and larval insects (del Hoyo et al. 1992). The species may also consume plant material on its breeding grounds (del Hoyo et al. 1992) (e.g. leaves and shoots) (Flint et al. 1984). Breeding site The nest is a shallow depression positioned on the ground (del Hoyo et al. 1992) in tall grass, among hummocks or under bushes (Flint et al. 1984), usually within 100 m of open water (occasionally up to 2-3 km away) (Kear 2005). The species usually nests in solitary pairs (del Hoyo et al. 1992, Kear 2005), but it may form loose congregations (del Hoyo et al. 1992) (e.g. on islands [Kear 2005]) with neighbouring nests as close as 3 m apart (Snow and Perrins 1998), and will also nest in association with gull or tern colonies (Kear 2005).
The species is highly susceptible to bycatch in fishing nets and is likely to be also caught in derelict fishing gear as observed for other scoter species (e.g. Good et al. 2009). The species may also suffer from resource competition with commercial fisheries exploiting marine benthic organisms and shellfish (Kear 2005).
Climate change is expected to impact this species in a number of ways. Remote sensing has shown the shrinkage and disappearance of lakes in Siberia which provide important breeding grounds for this species (Smith et al. 2005). In general, climate change is predicted to cause dramatic habitat changes in the Arctic region (Fox et al. 2015). Decreasing spring snow cover duration has been linked to declining Scoter populations in North America and this is likely due to trophic mismatch, so may also affect Siberian populations (Drever et al. 2011). Ocean acidification may lead to declines in molluscs which form a large part of Siberian Scoter diet (Steinacher et al. 2009, del Hoyo et al. 2017).
During moulting and winter aggregations, the species is highly susceptible to oil spills and other marine pollutants (del Hoyo et al. 1992, Kear 2005) and one catastrophic oil spill could potentially destroy a large proportion of the global population if it occurred in a key moulting or wintering area (Madge and Burn 1988). Oil and gas exploration is a pervasive threat in the Arctic and is likely to increase in the future (Poland et al. 2003, Henderson and Loe 2014), with human exploitation of natural resources in the taiga and lower tundra regions of its breeding range causing habitat degradation (Kear 2005).
The footprint of large offshore wind farms may exclude Siberian Scoter from some foraging areas and through disturbance, as it does reduce duck densities more than other seabird groups (Garthe and Hüppop 2004, Stewart et al. 2007), however the impact on other scoter species appears minor and the majority of the Siberian Scoter's range does not have any current plans for large-scale wind farms. Collision mortality is also likely to be a minor threat as collisions rates between ducks and wind turbines are low compared with other species groups, which is consistent with their high avoidance rates at offshore wind farms (Fox et al. 2015).
There is a small risk that future outbreaks of H5N1 (avian influenza) could pose a risk to the species (Melville and Shortridge 2006), however the disease is mostly asymptomatic in wild birds and there is no record of significant mortality in this species.
Text account compilers
Taylor, J., Arendarczyk, B., Fjagesund, T., Butchart, S., Hermes, C., Malpas, L., Palmer-Newton, A., Ekstrom, J., Stuart, A.
Moores, N., Pihl, S.
BirdLife International (2020) Species factsheet: Melanitta stejnegeri. Downloaded from http://www.birdlife.org on 19/09/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/09/2020.