Habitat and Ecology
Habitat and Ecology
Behaviour This species is dispersive in Europe, and migratory in Asia14. It starts to breed in late March or April14, sometimes solitarily but usually in dense colonies of up to 250 pairs14,16. Adults form monogamous pair bonds7. It departs from the colonies between the end of July and September, although a few remain until November15. It is gregarious during the winter, often occurring in large flocks and foraging communally and cooperatively in small groups16, although occasionally singly16. The birds return to their breeding sites in late-January to April, depending on the region15. Immature birds and non-breeders may remain in the wintering grounds year round15, or may stay with the breeding colonies16. They are often nomadic, especially in the Caspian Sea15. Habitat It occurs mainly at inland, freshwater wetlands but also at coastal lagoons, river deltas and estuaries2,7,8,14. Breeding It breeds on small islands in freshwater lakes14 or in dense aquatic vegetation14 such as reedbeds of Typha and Phragmites1,8,9,14 , often in hilly terrain15. A few breed in Mediterranean coastal lagoons8,15. The species makes use of habitats surrounding its breeding sites, including nearby islands and wetlands15. Non-breeding On migration, large lakes form important stop-over sites15. It typically winters on jheels and lagoons in India, and ice-free lakes in Europe14. It sometimes fishes inshore along sheltered coasts14. Diet It feeds almost entirely on fish, especially carp Cyprinus carpio, perch Perca fluviatilis, rudd scardinius erythrophthalmus, roach Rutilus rutilus, and pike Esox lucius in freshwater wetlands14, and eels, mullet, gobies and shrimps in brackish waters1,8. In its winter quarters on the Nile it takes mostly Siluridae15. In the Mikri Prespa breeding colony in Greece it feeds predominantly on the endemic fish species Chalcalburnus belvica18. Breeding site Most nests are situated amongst aquatic vegetation on floating or stationary islands isolated from the mainland to avoid mammalian predators1, 8, 9. They are occasionally built on open ground5,6,15. Nests usually consist of a pile of reeds, grass and sticks approximately 1m high and 0.5-1.5m in diameter14,15. It often tramples the vegetation between nests, and does not tend to nest in areas where such activities would generate deep mud15. The trampling activity damages the islands and therefore limits the number of years for which an island can be used for breeding17. On average sites in Greece were found to be used for three years in succession17. Artificial islands have proved successful as breeding sites in the past9.