Anser anser  

Behaviour This species is fully migratory although some populations in temperate regions are only sedentary¹ or locally dispersive⁵, occasionally making irregular movements in very icy winters¹. The species breeds from May or April in loose colonies^{1, 2}, after which flocks gather to undertake moult migrations to favoured areas (with good feeding opportunities and access to safe roosting sites)² to undergo a flightless moulting period lasting c.1 month⁵. The species is highly gregarious^{2, 3} outside of the breeding season³, with large concentrations forming during the post-breeding moult and before the autumn migration (e.g. flocks of up to 25,000 individuals)⁵. The species feeds diurnally, especially during the morning and evening, although non-breeding birds may also feed at night². It roosts at night and during the middle of the day on open water⁷, and may fly to feeding areas more than 10 km away from roosting sites² (optimal distance 2-5 km away)¹⁰. Habitat Breeding During the breeding season the species inhabits wetlands surrounded by fringing vegetation in open grassland¹, sedge or heather moorland⁴, arctic tundra, steppe or semi-desert from sea-level up to 2,300 m⁶. It nests near streams, saltmarshes², river flood-plains, reedy marshes, grassy bogs, damp meadows, reed-lined freshwater lakes and estuaries⁴ close to potential feeding sites such as meadows, grasslands, stubble fields and newly sown cereal fields². It requires isolated islands² in lakes⁴ or on along the coast² out of reach of land predators for nesting². In the autumn (before migration) the species also frequents agricultural land (e.g. sugar-beet, maize and cereal fields)². Non-breeding In the winter the species inhabits lowland farmland in open country^{1, 3}, swamps¹, lakes^{1, 3}, reservoirs³, coastal lagoons¹ and estuaries³. Diet The species is herbivorous, its diet consisting of grass¹, the roots, shoots, leaves, stems, seedheads and fruits of other herbaceous marsh vegetation^{1, 4}, aquatic plants⁴, and agricultural grain and potatoes (especially in the winter)¹. Breeding site The nest is a shallow construction of plant matter^{1, 6} placed among reedbeds, on the ground¹, in or at the base of trees, under bushes or in sheltered hollows on isolated wooded islands on lakes or along coasts^{2, 4}, as well as on rafts of vegetation in rivers⁶. Although the species is only semi-colonial, nests may be concentrated within a small area (e.g. placed 11 m apart on small islands)⁴. Management information On the Vejlerne nature reserve, Denmark, it was found that reedbeds left unharvested for 5-13 years supported the highest nesting densities of this species¹². Low nesting densities were found in reedbeds in the first four years after reed cutting, and no nests were found in reedbeds cut in the year of study (shoot density may have been too low to provide adequate cover) or in reedbeds left uncut for sixteen years (reed stems may have been too dense)¹².