Behaviour This species is predominantly migratory (del Hoyo et al. 1992) and travels over land making brief stop overs (Snow and Perrins 1998). It breeds from mid-May in solitary pairs with well-defined territories (del Hoyo et al. 1992) (non-breeders remaining in flocks separate from breeding pairs) (Kear 2005a). Adults undergo a post-breeding moult period between late-July and early-August when they become flightless for c.30 days (Kear 2005a) (5-6 weeks) (Scott and Rose 1996), males starting to moult before the females (Kear 2005a). Non-breeding individuals moult at the same time as breeders, but whilst breeding pairs tend to moult in their breeding territories non-breeders moult in large congregations (Kear 2005a). After moulting the species begins to migrate south from late-September to October (the precise timing determined by weather conditions) (Kear 2005a) and arrives on the wintering grounds by October or November (Madge and Burn 1988). The species departs for the breeding grounds again from March to April (Kear 2005a) or early-May (Madge and Burn 1988). Outside of the breeding season the species is highly sociable, migrating in small flocks or family groups (Madge and Burn 1988) and congregating into flocks of up to 300-400 individuals in the winter (Johnsgard 1978, Madge and Burn 1988). The species roosts on areas of open water adjacent to its feeding areas (Madge and Burn 1988). Habitat Breeding The species breeds on islands in or along the banks of shallow freshwater pools, lakes, slow-flowing rivers (del Hoyo et al. 1992), marshes, swamps and bogs (Kear 2005a), showing a preference for habitats with abundant emergent vegetation (Kear 2005a) and reedbeds (Johnsgard 1978) in taiga (coniferous forest) zones (Johnsgard 1978, Kear 2005a), birch forest zones (Johnsgard 1978) and shrub/forest tundra (Kear 2005a) (generally avoiding open tundra) (Johnsgard 1978, del Hoyo et al. 1992). Non-breeders may also be found in flocks (Kear 2005a) along sheltered coasts (del Hoyo et al. 1992) on estuaries, lagoons and shallow bays during this season (Snow and Perrins 1998). Non-breeding On migration the species frequents lakes, estuaries and sheltered coasts (Kear 2005a). It traditionally winters on freshwater lakes and marshes (Kear 2005a), floodlands (Snow and Perrins 1998), brackish lagoons and coastal bays (Kear 2005a) although low-lying coastal agricultural land (del Hoyo et al. 1992) and wet pastures (Snow and Perrins 1998) are now used increasingly (Kear 2005a). Diet The species is predominantly herbivorous (del Hoyo et al. 1992), its diet consisting of the leaves, stems and roots (Johnsgard 1978) of aquatic plants (e.g. algae and Zostera, Ruppia and Potamogeton spp.), grasses (del Hoyo et al. 1992), sedges and horsetails (Equisetum spp.) (Kear 2005a). During the winter the species also takes agricultural grain, vegetables (e.g. potatoes and turnips (Johnsgard 1978)) and acorns (del Hoyo et al. 1992), and on the breeding grounds young birds often take adult and larval insects (Johnsgard 1978) (e.g. emerging chironomids) (Kear 2005a). Adults may also supplement their diet with marine and freshwater mussels (Kear 2005a). Breeding site The nest is a large mound of plant matter (del Hoyo et al. 1992) built on dry ground or in reedbeds (Johnsgard 1978) on small islands in or along the edges of lakes, pools or rivers (Madge and Burn 1988). The same nest mound may be used over several years although it is often repaired and new material is added (Kear 2005a). Management information A study carried out at a wintering site in Denmark found that large wind turbines (towers 68 m high with blades 66 m in diameter, blades sweeping the heights of 35-101 m) pose less of a collision risk to the species than wind turbines of a medium height (towers 45 m high with blades 48 m in diameter, blades sweeping the heights of 21-69 m) (Larsen and Clausen 2002).

Conservation Actions Underway
Bern Convention Appendix II. EU Birds Directive Annex I. CMS Appendix II. In the U.K., the species is listed as Amber on the national Red List (Eaton et al. 2009).

Conservation Actions Proposed
Key sites should be identified and protected by legislation against all forms of development and habitat alteration. Strict legislation should also be enforced with regards to oil drilling and transportation. Power lines should be made more visible or moved and careful assessment made during planning of wind farm construction. Protection from hunting and persecution should also be implemented and enforced.