There are two recognised subspecies of Anser anser (Linnaeus 1758): ssp. anser (Linnaeus 1758) and ssp. rubrirostris (Swinhoe 1871) (UNEP-WCMC 2008).

This species is fully migratory although some populations in temperate regions are only sedentary or locally dispersive, occasionally making irregular movements in very icy winters. The species breeds from May or April in loose colonies after which flocks gather to undertake moult migrations to favoured areas (with good feeding opportunities and access to safe roosting sites) to undergo a flightless moulting period lasting c.1 month. The species is highly gregarious outside of the breeding season, with large concentrations forming during the post-breeding moult and before the autumn migration (e.g. flocks of up to 25 000 individuals). The species feeds diurnally, especially during the morning and evening, although non-breeding birds may also feed at night. It roosts at night and during the middle of the day on open water, and may fly to feeding areas more than 10 km away from roosting sites (optimal distance 2 to 5 km away) (source: BirdLife International 2008).

This adaptable goose occupies a wide variety of habitats associated with water in open country, usually where there is ample fringing vegetation and nearby grasslands. It winters on marshes, grasslands, farmland and coastal lagoons (Blair et al. 2002). During the breeding season the species inhabits wetlands surrounded by fringing vegetation in open grassland, sedge or heather moorland, arctic tundra, steppe or semi-desert from sea-level up to 2 300 meters. It nests near streams, saltmarshes, river flood-plains, reedy marshes, grassy bogs, damp meadows, reed-lined freshwater lakes and estuaries close to potential feeding sites such as meadows, grasslands, stubble fields and newly sown cereal fields. It requires isolated islands in lakes or on along the coast out of reach of land predators for nesting. In the autumn (before migration) the species also frequents agricultural land (eg: sugar-beet, maize and cereal fields). Non-breeding: in the winter the species inhabits lowland farmland in open country, swamps, lakes, reservoirs, coastal lagoons and estuaries (BirdLife International 2008).

The nest is a shallow construction of plant matter placed among reedbeds, on the ground, in or at the base of trees, under bushes or in sheltered hollows on isolated wooded islands on lakes or along coasts as well as on rafts of vegetation in rivers. Although the species is only semi-colonial, nests may be concentrated within a small area (eg: placed 11 meters apart on small islands (BirdLife International 2008).

The species is herbivorous, its diet consisting of grass, the roots, shoots, leaves, stems, seedheads and fruits of other herbaceous marsh vegetation, aquatic plants, and agricultural grain and potatoes (especially in the winter) (BirdLife International 2008).

The greylag goose has hybridized in captivity with 23 Anatidae species and with domestic geese. In the wild, hybridization as an isolated event has often been recorded, but since the 1970s, hybridization in the wild with other escaped geese and with feral/hybrid greylag geese has helped produce perhaps 1 ,000 hybrids (mostly of domestic/wild goose appearance) in the Netherlands and Germany (Blair et al. 2002). Feral/hybrid Greylag Goose will continue to thrive and are adapting to near non-migratory life in urban wetlands and gravel pits. Competition for breeding habitat between greylag and Canada geese is likely to increase. Increasing hybrid flocks in the Netherlands, Germany and elsewhere are likely to become a serious issue. Smaller waterbirds may experience stress. Eutrophication of ponds may become an issue. Wild birds may be genetically vulnerable (Blair et al. 2002).