Data Zone
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). There are conflicting data on the species's population trend, but until wider survey data are available the species is regarded as not declining sufficiently rapidly 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. If surveys do not locate the numbers that appeared to be missing from the Baltic Sea in recent years (2007-2009), this species is likely to qualify for uplisting.
Population justification
The total population has been estimated to number 1,600,000 individuals (Delany and Scott 2006), which probably includes c.1,070,000 mature individuals, assuming that they account for around 2/3 of the population. The European population is estimated at 107,000-131,000 pairs, which equates to 214,000-263,000 mature individuals (BirdLife International 2015).
Trend justification
An analysis of the population trend in the Baltic Sea suggests that a decline of 47.4% occurred between 1988-1993, when a total of c.783,000 birds wintered there, and 2007-2009, when c.412,000 birds were counted (Skov et al. 2011). Extrapolation of these data suggests that this is equivalent to a decline of c.55% over three generations (23 years, based on a generation length of c.7.5 years). However, data from other sources contradict this apparent decline. Data on passage migrants in the Gulf of Finland are not indicative of a decline, with stable or positive trends observed since the 1970s (M. Ellermaa in litt. 2012, A. Lehikoinen et al. in litt. 2012). Numbers breeding in Finland appear to have been stable or to have increased slightly since the 1990s (M. Ellermaa in litt. 2012, A. Lehikoinen et al. in litt. 2012), with the same trend in Sweden since the 1970s (per N. Holmqvist in litt. 2012). These conflicting data sets imply that a large proportion of the wintering population could have shifted to the North Sea (M. Ellermaa in litt. 2012). This theory is supported by increased numbers in British waters during the winter of 2009/2010 (M. Hancock in litt. 2012).
This species breeds in Iceland, eastern Greenland (Denmark) and northern United Kingdom, across Scandinavia and northern parts of western and central Russia (e.g. Collinson et al. 2006). It winters in the Baltic Sea, off the Atlantic coast of Europe and North Africa, south to Mauritania, and in the western Mediterranean (del Hoyo et al. 1992, Delany and Scott 2006).
Behaviour This species is strongly migratory (del Hoyo et al. 1992) and often travels considerable distances over land making brief stop-overs on inland waters (Madge and Burn 1988). It arrives on its breeding grounds between late-April and May and breeds from late-May onwards (Madge and Burn 1988) in highly dispersed (Kear 2005) solitary pairs (del Hoyo et al. 1992). After mating (from June onwards) males migrate long distances prior to their flightless moult, most travelling in small groups to inshore or offshore coastal waters (Madge and Burn 1988). Females and juveniles leave the breeding grounds in September (Madge and Burn 1988). The species is highly gregarious when not breeding (Madge and Burn 1988) with males forming large congregations during the flightless moulting period (Kear 2005) and large flocks of several hundred to a thousand (Snow and Perrins 1998) or occasionally over 100,000 individuals occurring during winter (Scott and Rose 1996). Non-breeders often oversummer on the wintering grounds (Madge and Burn 1988). Habitat Breeding The species breeds on Arctic dwarf heath (Snow and Perrins 1998, Kear 2005) or boggy tundra on pools, small lakes, streams (del Hoyo et al. 1992) and slow-flowing rivers (Snow and Perrins 1998). It shows a preference for freshwater habitats (del Hoyo et al. 1992) with low banks (Flint et al. 1984), small islets (Kear 2005) and high abundances of aquatic invertebrate and plant life positioned in swampy valleys or among mossy bogs (Flint et al. 1984), especially where suitable shrubs (e.g. willow or birch) and herbaceous vegetation are available for nesting cover (Johnsgard 1978, Snow and Perrins 1998, Kear 2005). It generally avoids areas with steep slopes or wetlands enclosed by forest (Kear 2005). Non-breeding Although the species may use freshwater lakes on migration (Madge and Burn 1988, Kear 2005) the majority moult and overwinter at sea (Kear 2005) on shallow inshore waters less than 20 m deep (Kear 2005) (optimally 5-15 m) (Scott and Rose 1996) with abundant benthic fauna (Kear 2005), generally between 500 m and c.2 km from the shore (Snow and Perrins 1998). Diet Its diet consists predominantly of molluscs, especially during the winter (del Hoyo et al. 1992), although it occasionally takes other aquatic invertebrates such as crustaceans (del Hoyo et al. 1992) (e.g. barnacles and shrimps) (Johnsgard 1978), worms (del Hoyo et al. 1992), echinoderms, isopods, amphidods (Kear 2005) and insects (e.g. midges and caddisflies [del Hoyo et al. 1992]) as well as small fish (del Hoyo et al. 1992) and fish eggs (Snow and Perrins 1998). On the breeding grounds the species may also consume plant matter (del Hoyo et al. 1992) such as seeds, roots and tubers (del Hoyo et al. 1992) and the vegetative parts of aquatic plants (Flint et al. 1984). Breeding site The nest is a scrape on the ground hidden amongst vegetation (del Hoyo et al. 1992) close to water (Madge and Burn 1988, Kear 2005) or placed further away in dwarf heath (Kear 2005).
Oil spills and chronic oil pollution threaten this species in the winter moulting period where large and highly vulnerable concentrations of the population occur, while development associated with oil drilling sites can cause additional, low-level impacts through human disturbance and the degradation of food resources (Gorski et al. 1977, Nikolaeva et al. 2006). Some large populations border oil fields and proximity to drilling and transport puts the population at high risk of oil pollution (Nikolaeva et al. 2006). However, one study found that although the 1996 Sea Empress oil spill in Carmarthen Bay resulted in a rapid and drastic reduction in Common Scoter numbers in the area, complete recovery occurred after three winters with no observable long-term effects (Banks et al. 2008).
Climate change is thought to negatively impact the species at present and in the future through habitat loss and ecosystem degradation. Wetlands provide important breeding grounds for this species, and remote sensing and imaging has shown shrinkage and disappearance of lakes in Siberia (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 in North American boreal regions has been linked to population declines of Scoters, likely due to trophic mismatch (Drever et al. 2011). Ocean acidification may lead to declines in molluscs which form a large part of their diet (Steinacher et al. 2009, Carboneras and Kirwan 2017). Eutrophication in the Baltic Sea resulting from agricultural run-off, could also cause the loss of key prey items, e.g. bivalves (Skov et al. 2011).
The risk of bycatch is thought to affect a majority of the population, as reported in the Gulf of Gdańsk (Stempniewicz 1994), and the commercial exploitation of benthic shellfish poses an additional threat, through competition for food resources (Kear 2005). Further threats to food resources include the loss of benthic habitats caused by sand and gravel extraction, although Skov et al. (2011) suggest that in the present-day Baltic region, this is occurring at insufficient levels to be responsible for declines in waterbirds. Hunting is contributing to mortality in some parts of the species’ range, but not thought to drive significant population decline. In Denmark, c.2,800-5,200 Common Scoters are harvested per year (Bregnballe et al. 2006) but no data is available for other countries, although hunting of Common Scoters is legal in some EU countries (HELCOM 2013b). Interaction with wind farms could pose a potential threat to the species. While Stewart et al. (2007) showed that duck densities were more adversely affected by wind farms than other groups of species, Dürr (2013) found the opposite, stating that collision rates between ducks and wind turbines are low compared to other species groups. Avian influenza is present in the population, but as yet there is no evidence that it has caused significant mortality events (Melville and Shortridge 2006, Gudmundsson et al. 2010). High-speed ferries have been suggested as a major cause of Common Scoter disturbance by a study in the Kattegat Sea, Denmark (Larsen and Laubek 2005).
Conservation Actions Underway
EU Birds Directive Annex II and III. CMS Appendix II. The following information refers to the species's range within Europe: Current measures for the protection of this species are not sufficient and the species suffers from a lack of knowledge and research interest (Kear 2005). In the U.K. the species is listed as Red on the national Red List and is a U.K. Priority Species and Biodiversity Action Plan species. It is also listed as Endangered on the Red List of Baltic Wintering Birds (HELCOM 2013a). Research and monitoring has been initiated by several organisations to identify the driving factors behind its decline and better understand the species's movements (Wildfowl and Wetlands Trust 2013).
Conservation Actions Proposed
The following information refers to the species's range within Europe: Management actions at non-breeding sites are essential to maintain the health of this species. Measures should be taken to minimise bycatch in fisheries, regulate shipping traffic, implement and enforce hunting regulations (Bellebaum et al. 2012, HELCOM 2013b), prevent accidental and chronic oil pollution and preserve feeding grounds (HELCOM 2013b). Research and monitoring should continue, particularly into the effects of climate change on the species and its prey (Bellebaum et al. 2012).
Text account compilers
Martin, R., Palmer-Newton, A., Stuart, A., Taylor, J., Arendarczyk, B., Butchart, S., Calvert, R., Ashpole, J, Ekstrom, J., Fjagesund, T., Hermes, C., Malpas, L.
Contributors
Bianki, V., Rajasarkka, A., Ellermaa, M., Tiainen, J., Below, A., Lehikoinen, E., Bellebaum, J., Pessa, J., Hancock, M., Kharitonov, S., Hario, M., Holmqvist, N., Kontiokorpi, J., Pihl, S., Mineev, Y., Mineev, O., Kharitonova, I., Valkama, J., Lehtiniemi, T., Lehikoinen, A., Mikkola-Roos, M.
Recommended citation
BirdLife International (2024) Species factsheet: Common Scoter Melanitta nigra. Downloaded from
https://datazone.birdlife.org/species/factsheet/common-scoter-melanitta-nigra on 27/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 27/12/2024.