The greylag is the largest and bulkiest of the grey geese of the genus Anser, but is more lightly built and agile than its domestic relative. It has a rotund, bulky body, a thick and long neck, and a large head and bill. It has pink legs and feet, and an orange or pink bill with a white or brown nail (hard horny material at tip of upper mandible). It is 74 to 91 centimetres (29 to 36 in) long with a wing length of 41.2 to 48 centimetres (16.2 to 18.9 in). It has a tail 6.2 to 6.9 centimetres (2.4 to 2.7 in), a bill of 6.4 to 6.9 centimetres (2.5 to 2.7 in) long, and a tarsus of 7.1 to 9.3 centimetres (2.8 to 3.7 in). It weighs 2.16 to 4.56 kilograms (4.8 to 10.1 lb), with a mean weight of around 3.3 kilograms (7.3 lb). The wingspan is 147 to 180 centimetres (58 to 71 in). Males are generally larger than females, with the sexual dimorphism more pronounced in the eastern subspecies rubirostris, which is larger than the nominate subspecies on average.

The plumage of the greylag goose is greyish-brown, with a darker head and paler breast and belly with a variable amount of black spotting. It has a pale grey fore-wing and rump which are noticeable when the bird is in flight or stretches its wings on the ground. It has a white line bordering its upper flanks, and its wing coverts are light-coloured, contrasting with its darker flight feathers. Its plumage is patterned by the pale fringes of the feathers. Juveniles differ mostly in their lack of black-speckling on the breast and belly and by their greyish legs.

The greylag goose has a loud cackling call similar to that of the domestic goose, "aahng-ung-ung", uttered on the ground or in flight. There are various subtle variations used under different circumstances, and individual geese seem to be able to identify other known geese by their voices. The sound made by a flock of geese resembles the baying of hounds. Goslings chirp or whistle lightly, and adults hiss if threatened or angered.

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Taxonomy