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 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 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 is estimated to number c.2,700,000-4,700,000 individuals (Wetlands International 2015). The Russian national population is estimated at c.100,000-1 million breeding pairs and c.10,000 wintering individuals (Brazil 2009). The European population is estimated at 489,000-623,000 pairs, which equates to 977,000-1,250,000 mature individuals (BirdLife International 2015).
The overall population trend is stable, although some populations have unknown trends (Wetlands 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). In Europe the population size is estimated to be stable (BirdLife International 2015).
This species ranges across the boreal forests of Scandinavia, eastern Europe, Russia, Mongolia, northern China, Canada, Alaska and northern USA. Its wintering range is equally broad, encompassing the coast of northern Europe including inland United Kingdom, scattered coastal and inland water bodies in south-eastern Europe (e.g. Turkey) and central Asia, the coasts of eastern China, Korea, Japan and the Kamchatkha Peninsula (Russia), the Pacific coast of Canada and the Alaskan coast and inland USA (del Hoyo et al. 1992).
Behaviour Most of this species is fully migratory although it may only travel short distances (Kear 2005), and certain populations in the north-west of Europe may also be sedentary (del Hoyo et al. 1992). The species breeds from April in solitary pairs (del Hoyo et al. 1992), after which it undertakes short northerly moult migrations to coastal areas, large lakes and rivers (Kear 2005) to undergo a period of flightless moult lasting 3-4 weeks (males leave for this moult migration first while females are still incubating) (Scott and Rose 1996). Large moult gatherings are common during this period, males arriving at such gatherings in early-June and numbers peaking in late-August when adult females arrive (Scott and Rose 1996). The southward autumn migration begins in late-August with most arriving in the winter quarters by early-December (Scott and Rose 1996). Females tend to migrate further than males and juveniles migrate further than adults (Madge and Burn 1988, Scott and Rose 1996). The return migration to the breeding areas occurs as early as mid-February, the species timing its arrival to coincide with the thawing and appearance of open water (Scott and Rose 1996, Kear 2005). Non-breeders may also over-summer on wintering grounds (Madge and Burn 1988). The species is gregarious outside of the breeding season usually being observed in small scattered groups or in small flocks on migration (Scott and Rose 1996, Snow and Perrins 1998, Kear 2005). Several hundred individuals may roost together (Snow and Perrins 1998) and large flocks often gather to feed at sewage outfalls (del Hoyo et al. 1992) during the winter, although the species rarely occurs in very large flocks (Scott and Rose 1996).
Habitat The species is restricted to water close to the shore and less than 10 m deep, showing a preference for waters 4 m deep (Scott and Rose 1996, Snow and Perrins 1998). Breeding When breeding the species shows a preference for oligotrophic lakes devoid of fish but with abundant invertebrate life (Johnsgard 1978, Kear 2005), and requires tree-holes (or artificial nestboxes) for nesting (del Hoyo et al. 1992). Suitable habitats include freshwater lakes, pools, rivers and deep marshes surrounded by coniferous forest (Johnsgard 1978, del Hoyo et al. 1992). Non-breeding The species winters mainly at sea on inshore waters, shallow bays, estuaries and coastal lagoons (del Hoyo et al. 1992, Scott and Rose 1996, Kear 2005), especially in the vicinity of sewage outfalls (del Hoyo et al. 1992). Further to the south and on migration the species may also frequent large rivers, lakes and reservoirs (Scott and Rose 1996, Kear 2005).
Diet The diet of the species consists predominantly of aquatic invertebrates such as molluscs, worms, crustaceans, aquatic insects and insect larvae (e.g. dragonflies, damsel flies and may flies) (Johnsgard 1978, del Hoyo et al. 1992), as well as amphibians, small fish and some plant material (mainly in the autumn) such as seeds, roots and the vegetative parts of aquatic plants (del Hoyo et al. 1992).
Breeding site The species nests in hollows of mature trees (e.g. aspen, spruce or oak) formed by woodpeckers or by bacterial or fungal heart-rot invasions that have internal cavity diameters of c.20 cm, although the height of the hollow does not seem to be important (Johnsgard 1978, Flint et al. 1984, del Hoyo et al. 1992, Kear 2005). The species will preferentially nest in trees in open stands near water or solitary trees on the edges of marshes, rather than in trees in dense stands in order to increase the ease of entry by flying (Johnsgard 1978, Madge and Burn 1988). The species will also nest in artificial nest-boxes (del Hoyo et al. 1992).
Management information In Scotland, UK the introduction of a sewage treatment scheme in the Firth of Forth (a large marine bay) resulted in a considerable reduction in the abundance of the species, with feeding flocks only remaining at outfalls where sewage continued to be discharged in large quantities (Campbell 1984). It was unclear whether the changes in the species's distribution were due to reductions in the number of food items borne in the sewage or to reductions in aquatic invertebrate abundance as a result of the new treatment system (Campbell 1984). In some areas nestbox erection programmes have been shown to cause significant range expansions and population increases (Dennis 1987, del Hoyo et al. 1992), although an experiment in southern Finland found that even though nestbox provision increased breeding numbers of the species there was a negative density-dependent effect on reproductive output (i.e. the number of fledged young did not increase despite an increase in breeding pairs) (Poysa and Poysa 2002). Nesting habitats in general may also benefit from a more extended rotation of timber harvesting (Kear 2005).
The species is threatened by wetland degradation and loss in North America and is susceptible to atmospheric acid deposition (e.g. acid rain) throughout a large part of its breeding range (Kear 2005). The main threat to the species in its wintering range is pollution, e.g. from coastal oil spills or other pollutants from sewage outfalls (del Hoyo et al. 1992). Modern forestry management work is also limiting the suitable area of breeding habitat by removing old and decaying trees with likely nest holes (Hagemeijer and Blair 1997). The timber industry is thought to be compromising the population in large parts of the range. The placing of nest-boxes to compensate for the loss of natural nesting sites has not been very effective, as the species reaches an apparent density-dependent plateau in breeding success (Finland), which may indicate that nesting resource is not the primary limiting factor constraining the population. However, in other parts of the species' range (North America) use of nest-boxes has been found to increase the breeding range and productivity of Common Goldeneye. Historically, an estimated 100,000–250,000 were shot annually in north-west and central Europe. The species is still hunted at sustainable levels in Denmark (Bregnballe et al. 2006), while hunting elsewhere has unquantified effects on the global populations (Kear 2005), though not thought to drive any significant declines. Lead shot ingestion does not appear to be a significant risk, at least when compared to some other species of seaducks (Carboneras et al. 2014). The introduction of invertebrate-eating fish such as Perch, Perca spp., to many lakes where they were not formerly present leads to increased resource competition which has been experimentally shown to negatively affect the Common Goldeneye (Nummi et al. 2016).
Conservation Actions Underway
CMS Appendix II. EU Birds Directive Annex II. The following information refers to the species's European range only: In some areas nest-box erection programmes have been shown to cause significant range expansions and population increases (Dennis 1987, Carboneras et al. 2014), although an experiment in southern Finland found that even though nest-box provision increased breeding numbers of the species there was a negative density-dependent effect on reproductive output (i.e. the number of fledged young did not increase despite an increase in breeding pairs) (Poysa and Poysa 2002).
Conservation Actions Proposed
The following information refers to the species's European range only: In general nesting habitats may benefit from a more extended rotation of timber harvesting (Kear 2005) and the species may benefit from the introduction of strict legislation on oil transportation. Monitoring and research should be introduced to determine the impact of hunting on this species.
Text account compilers
Stuart, A., Calvert, R., Ekstrom, J., Butchart, S., Ashpole, J, Fjagesund, T., Hermes, C., Malpas, L., Martin, R.
BirdLife International (2019) Species factsheet: Bucephala clangula. Downloaded from http://www.birdlife.org on 19/09/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/09/2019.