Behaviour Truly wild populations of this species are migratory (particularly where displaced by cold weather) (del Hoyo et al. 1992, Snow and Perrins 1998) although European and feral populations are essentially sedentary (Johnsgard 1978, del Hoyo et al. 1992, Scott and Rose 1996, Snow and Perrins 1998) or only locally migratory or nomadic (Scott and Rose 1996, Snow and Perrins 1998). The species breeds during the local spring (del Hoyo et al. 1992, Kear 2005) as isolated pairs in well-defended territories (del Hoyo et al. 1992). After breeding the adults may gather in large concentrations of thousands or more (Johnsgard 1978, Madge and Burn 1988) on selected waters (Madge and Burn 1988) (non-breeders in northern Europe migrating to such gatherings (Snow and Perrins 1998)) between July and August (Scott and Rose 1996) to undergo a flightless moulting period lasting for 6-8 weeks (Kear 2005a). Although not noticeably sociable in many areas during the winter (Johnsgard 1978) the species may flock in groups of several thousands on favoured waters (Johnsgard 1978, Madge and Burn 1988, Scott and Rose 1996). Habitat The species inhabits a variety of lowland freshwater wetlands (del Hoyo et al. 1992) such as shallow lakes (Kear 2005), ponds (Madge and Burn 1988), lagoons, marshes (del Hoyo et al. 1992), reedbeds (del Hoyo et al. 1992, Snow and Perrins 1998) and slow-flowing rivers (Kear 2005) (showing a preference for clean, weed-filled streams over larger, polluted rivers) (Johnsgard 1978). It is also common on artificial waterbodies such as reservoirs, gravel-pits, ornamental lakes (del Hoyo et al. 1992), ditches (Snow and Perrins 1998) and canals (Scott and Rose 1996), and will graze on grassland and agricultural land (e.g. arable cereal fields) (Kear 2005). Moulting congregations of adults and non-breeders (Snow and Perrins 1998) may also utilise brackish or saline habitats (Johnsgard 1978) including brackish marshes (Kear 2005), estuaries and sheltered coastal sites (del Hoyo et al. 1992) (e.g. brackish lagoons [Kear 2005] and bays [Madge and Burn 1988]). Diet Its diet consists predominantly of leaves and the vegetative parts of aquatic plants (Johnsgard 1978, del Hoyo et al. 1992) and grasses (del Hoyo et al. 1992) as well as algae (Johnsgard 1978) and grain (del Hoyo et al. 1992), occasionally also taking small amphibians (Johnsgard 1978, del Hoyo et al. 1992) (frogs, toads and tadpoles) (Snow and Perrins 1998) and aquatic invertebrates (e.g. molluscs, insects and worms) (Johnsgard 1978, del Hoyo et al. 1992). Breeding site The nest is a large mound of aquatic vegetation (del Hoyo et al. 1992, Kear 2005) placed close to or floating on shallow water (del Hoyo et al. 1992, Kear 2005) or amongst reeds (del Hoyo et al. 1992). Breeding pairs often re-use nesting sites from previous years if the it was successful (Johnsgard 1978). Management information A control of the breeding output of the species (brood reduction) carried out in the Wylye Valley, UK to try to alleviate the species' negative impacts on fisheries (e.g. by overgrazing submergent riverine vegetation) was found to be ineffective as it had an insignificant impact on local population sizes (possibly due to immigration from surrounding areas) (Watola et al. 2003).

Conservation Actions Underway
EU Birds Directive Annex II. CMS Appendix II.