Range & Status
Palearctic; in Britain and Ireland 7000 pairs breed; 129,500 in winter.
Cornwall: chiefly a winter visitor and passage migrant to inland waters where very small numbers remain in summer (1-3 pairs probably breed annually Colliford and Crowdy and since 2003 up to three broods of ducklings per summer at Bake Lakes and elsewhere in the vicinity). Winter numbers total some 300; the main site is Loe Pool (up to 100), with up to 50 on Argal, Swanpool, Stithians and Siblyback. Isles of Scilly: odd pairs have nested on Tresco in most years since 1983, with small numbers in winter.
Habitat & Ecology
Freshwater lakes and reservoirs, locally on upper reaches of estuaries (especially in cold weather).
Nest sites are vulnerable to flooding if water levels rise.
Part of Colliford Reservoir is a Cornwall Bird Watching and Preservation Society reserve. Listed (long list) as a globally threatened/declining species (BSGR, 1995).