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 hence it is not believed to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very 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.
Wetlands International (2016) estimated the population at 612,000-640,000 individuals. In Europe the breeding population is estimated at 700-1,300 pairs, which equates to 1,400-2,600 mature individuals (BirdLife International 2015).
The overall population trend is thought to be stable, although some populations have unknown trends (Wetlands International 2016). In North America, the species has undergone a small or statistically insignificant increase over the last 40 years (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). In Europe, the population is projected to be decreasing by 30-49% in the 29 years (three generations) between 2000, when the declines are estimated to have begun, and 2029, and by at least 20% in 20 years (two generation lengths) (BirdLife International 2015).
This species breeds in much of Canada and Alaska, parts of northern U.S.A., southern parts of Greenland (to Denmark) and in Iceland. It winters on coasts or on larger lakes over a much wider area including the Atlantic coast of Europe from Finland to Portugal and the western Mediterranean, the Atlantic coast of North America down to northern Mexico, and the Pacific coast of North America from northern Mexico to the tip of Alaska (U.S.A.) (del Hoyo et al 1992).
Behaviour This species is strongly migratory, with inland breeding populations moving south or to the coast after breeding (del Hoyo et al 1992). The species breeds from May onwards in isolated solitary pairs, nesting later further to the north depending on the timing of the snow melt (del Hoyo et al 1992). Adults become flightless for a short time in late-winter when they moult their flight feathers (Godfrey 1979). During winter, the species occurs singly, in pairs or in small loose flocks in marine habitats, occasionally also forming large congregations of c.300 (Godfrey 1979, Snow and Perrins 1998, del Hoyo et al 1992). Habitat Breeding The species breeds on large, deep freshwater lakes in coniferous forest or on open tundra (del Hoyo et al 1992). For nesting, it requires clear water with a visibility of at least 3-4 m and small islands (less than 2.5 ha) (Rimmer 1992). Non-breeding It winters along the coast on exposed rocky shores, sheltered bays, channels and sheltered inlets, preferring shallow inshore waters (del Hoyo et al 1992, Rimmer 1992, Snow and Perrins 1998). It may also be found inland on lakes and reservoirs during this season, although this is largely influenced by the weather (del Hoyo et al 1992, Rimmer 1992, Snow and Perrins 1998). Diet Its diet consists predominantly of fish as well as crustaceans, molluscs, aquatic insects, annelid worms, frogs, other amphibiansand plant matter (e.g. Potamogeton spp., willow Salix spp. shoots, roots, seeds, moss and algae) (del Hoyo et al 1992). Breeding site The nest is a mound of plant matter screened by vegetation and placed near the water's edge on islands, islets or promontories (del Hoyo et al 1992, Snow and Perrins 1998).
Relatively high levels of mortality from commercial gillnets have been recorded, e.g. in Chesapeake Bay, 21% of birds killed were this species (Forsell 1999) and bycatch appears relatively frequent in the great lakes, with up to 50 caught in a single net in a week (Evers et al. 2010). This indicates the potential for significant indiscriminate mortality, though this may be an extreme example and efforts to improve fishing gear to reduce this bycatch have been generally effective (Carey 1993). May also be vulnerable to human disturbance and pollution of inland breeding lakes.
Conservation Actions Underway
The species is listed under Appendix II of the Convention on Migratory Species and under the African Eurasian Waterbird Agreement. It is listed in Article I under the EU Birds Directive. In Europe, it occurs in 20 IBAs, including in Iceland, Norway (Svalbard and mainland Norway), Ireland, the United Kingdom and in Spain. It is a listed species in 83 Special Protection Areas in the EU Natura 2000 network.
Conservation Actions Proposed
Protect Important Bird Areas across range states and identify and designate additional important sites. Identify sites and areas where high gillnet bycatch is occurring, and develop effective mitigation solutions. Manage coastal and inland developments surrounding important breeding areas. Develop rapid and trans-boundary response plans to coastal oil spills. There is evidence that introducing floating nesting platforms on lakes is successful in increasing the reproductive success of the species (Piper et al. 2002), and that nest losses caused by flooding can be reduced by controlling water levels during the nesting period (Rimmer 1992). Mortality from entanglement and drowning in fishing nets could also be reduced by using fish traps with openings at the top to allow birds to escape, or by checking traps more regularly for captured birds (Rimmer 1992).
Text account compilers
Stuart, A., Butchart, S., Ashpole, J, Calvert, R., Bennett, S., Ekstrom, J., Fjagesund, T., Hermes, C., Malpas, L.
BirdLife International (2019) Species factsheet: Gavia immer. Downloaded from http://www.birdlife.org on 17/02/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/02/2019.