On migration this species may form large flocks of 200–1,200 individuals, with similar concentrations occurring on rich marine fishing grounds during the winter (Billerman et al. 2020). The species breeds on freshwater pools or lakes in open moorland, blanket bogs (Billerman et al. 2020) or open and wet peatland habitats (Campbell 1987). Outside of the breeding season the species frequents inshore waters along sheltered coasts, occasionally occurring inland (Billerman et al. 2020) on lakes, pools, reservoirs and rivers (Snow and Perrins 1998). Its diet consists predominantly of fish as well as crustaceans, molluscs, frogs, fish spawn (Billerman et al. 2020), aquatic insects, annelid worms (Snow and Perrins 1998) and plant matter (Billerman et al. 2020). In winter its diet is almost predominantly fish, and in the Baltic Sea they opportunistically feed on spawning Herring, Smelt and Percids.

Although the generation length for both EU and Europe regional assessments were calculated using the same methodology, new information arriving after the EU assessments were undertaken gave rise to an update in the generation lengths. This new information was then used for the Europe level assessments giving rise to a difference between the generation lengths used for the EU and Europe regions.

In Europe, the species breeds primarily in Greenland and the European part of Russia, with small numbers in Norway, Iceland, Sweden and the United Kingdom.

Conservation Actions Underway
The species is listed on Annex II of the Convention on Migratory Species, and is listed under the African Eurasian Waterbird Agreement. Listed on Annex II of the Bern Convention, and Annex I of the EU Birds Directive. Listed as critically endangered on the HELCOM convention. There are 58 Important Bird and Biodiversity Areas for this species. Within the EU it occurs and is protected in 426 Special Protection Areas. Since the 1970s, conservation work in Finland has included building artificial rafts for this species to reduce predation risk, which has led to higher breeding success in some areas. Within the North Sea (Germany) work is underway to test alternative fishing gears to gillnets, while in Lithuania gillnet bycatch mitigation is being trialled.

Conservation Actions Proposed
Development of mitigation measures for gillnet bycatch for commercial and artisanal fishing vessels. Prevention of chronic oil pollution and oil spill events, and development of rapid, trans-boundary plans for oil spill response. Protection of feeding grounds, and regulations for vessel traffic, management of recreational activities at important breeding and non-breeding sites, careful siting of windfarms away from critical habitat or migration pathways.