Behaviour The species is fully migratory (Snow and Perrins 1998) or locally dispersive (e.g. in Europe) (del Hoyo et al. 1992) and breeds from mid-April to early-June (Madge and Burn 1988) in single pairs or loose groups (del Hoyo et al. 1992). Males and non-breeders moult and become flightless for four weeks between June and August (females moulting one month later) (Scott and Rose 1996) prior to which they may make extensive moult migrations which take them considerable distances from the breeding waters (Madge and Burn 1988). Once this post-breeding moult is complete the species departs for its winter quarters, arriving there from October onwards (Madge and Burn 1988). The species is highly gregarious for most of the year (Snow and Perrins 1998) and although it is more commonly found in small groups (Madge and Burn 1988) it often forms large concentrations (Madge and Burn 1988, Scott and Rose 1996) of several hundred individuals (Scott and Rose 1996) in moulting and wintering areas (Madge and Burn 1988). It feeds diurnally, being most active during the early morning and evening (Kear 2005). Habitat The species inhabits inland deep fresh or brackish (del Hoyo et al. 1992) reed-fringed lakes, rivers, or saline and alkaline lagoons (Kear 2005) in open country (del Hoyo et al. 1992), also occurring (less often) on estuaries, river deltas and other sheltered coastal habitats (del Hoyo et al. 1992) on passage (Madge and Burn 1988) or during the winter (Scott and Rose 1996). Diet The diet of this species consists predominantly of the roots, seeds and vegetative parts of aquatic plants (Johnsgard 1978, del Hoyo et al. 1992) (e.g. Chara spp. (del Hoyo et al. 1992), Hippurus spp., hornworts Ceratophyllum spp., pondweeds Potamogeton spp., milfoil Myriophyllum spp. (Johnsgard 1978) and especially stonewort Nitellopsis obtusa (Ruiters et al. 1994)), although it will occasionally also take aquatic invertebrates (del Hoyo et al. 1992) (e.g. molluscs) (Johnsgard 1978), amphibians and small fish (del Hoyo et al. 1992). Breeding site The nest is constructed of roots, twigs and leaves near water (del Hoyo et al. 1992, Kear 2005) on the ground in dense vegetation or on floating mats of vegetation amidst reedbeds (Johnsgard 1978). Although the species usually breeds well-dispersed, neighbouring pairs may sometimes nest as close as 30 m apart (Snow and Perrins 1998, Kear 2005). Management information A study in Czechia found that fish ponds with a fish stock density of less than 400 kg ha¹, water transparency of more than 50 cm, mixed fish stocks (e.g. tench and pike or perch) rather than monospecific stocks (e.g. of carp or other herbivorous fish species), and systems that include ponds with fish fry are more likely to have high abundances of aquatic vegetation and are therefore more successful in supporting breeding pairs of this species (Musil 2006).

Conservation Actions Underway
CMS Appendix II. EU Birds Directive Annex II. The species is listed in the Red Book of endangered species in seven countries in the European Union (Defos du Rau 2002).

Conservation Actions Proposed
The following information refers to the species's European range only: Long-term monitoring should be continued and extended to cover all potential wintering sites and formal programs for monitoring hunting bags should be introduced. Research is needed on the species's population dynamics and habitat selection to help inform conservation measures, hunting regulation and the restoration of habitat (Defos du Rau 2002). The protection of key wetland sites is also needed (Tucker and Heath 1994).