This species occurs mainly on inland, freshwater wetlands but also at coastal lagoons, river deltas and estuaries (Peja et al. 1996, Crivelli et al. 1997, Mix and Bräunlich 2000, Billerman et al. 2020). Typically winters on ice-free lakes in Europe (Elliot et al. 2014). It starts to breed in late March and April (Billerman et al. 2020), sometimes solitarily but usually in dense colonies of up to 250 pairs (Cramp et al. 1977, Billerman et al. 2020). Adults form monogamous pair bonds (Mix and Bräunlich 2000). It leaves the colonies between the end of July and September, although a few remain until November (Nelson 2005). It is gregarious during the winter, often occurring in large flocks and foraging communally and cooperatively in small groups (Cramp et al. 1977).  Immature birds and non-breeders may remain in the wintering grounds year round (Nelson 2005), or may stay with the breeding colonies (Cramp et al. 1977).

Birds return to the breeding sites in late-January to April, depending on the region (Nelson 2005). It breeds on small islands in freshwater lakes or in dense aquatic vegetation such as reedbeds (Crivelli 1994, Peja et al. 1996, Pyrovetsi 1997, Billerman et al. 2020), often in hilly terrain (Nelson 2005). A few breed in Mediterranean coastal lagoons (Peja et al. 1996, Nelson 2005). Nests typically consist of a pile of reeds, grass and sticks approximately 1 m high and 0.5–1.5 m in diameter (Nelson 2005, Billerman et al. 2020). They are usually situated amongst aquatic vegetation on floating or stationary islands isolated from the mainland to avoid mammalian predators (Crivelli 1994, Peja et al. 1996, Pyrovetsi 1997) but occasionally may be built on open ground (Hatzilacou 1993, Hatzilacou 1999, Nelson 2005). Artificial islands may also be used for nesting (Pyrovetsi 1997, Billerman et al. 2020). It feeds almost entirely on fish (Tucker and Heath 1994). The species is dispersive in Europe, moving only short distances typically within the eastern Mediterranean (Billerman et al. 2020).

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 Greece, with significant numbers in Russia, Turkey, Romania and Bulgaria.

Conservation Actions Underway
CITES Appendix I. CMS Appendix I and II. EU Birds Directive Annex I. Bern Convention Appendix II. Conservation efforts have reduced the impact of the major threats in Europe (Crivelli et al. 1997). Marking and dismantling of power-lines (Crivelli et al. 1997), the provision of breeding platforms in Turkey, Greece, Bulgaria and Romania and rafts in Greece and Bulgaria, together with wardening (Hatzilacou 1999), water level management and education programmes at key sites, have reduced mortality and increased breeding success. A first European Action Plan was published in 1996 (Billerman et al. 2020) and reviewed in 2010 (Barov and Derhé 2011). An International Single Species Action Plan was published in 2018 (Catsadorakis and Portolou 2018) under the frameworks of AEWA, CMS and EAAFP.

Conservation Actions Proposed
Monitor breeding, wintering numbers and ecological changes at key sites. Sustainably manage wetlands. Establish wardened non-intrusion zones around breeding colonies. Bury power-lines or replace with more visible cable. Legally protect the species and its habitat in range states. Conduct public awareness campaigns and mediate potential conflicts with fishermen. Prevent poaching and overexploitation of fish.