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.
These geese normally pair for life, so courtship only occurs at the time of first maturity. The nest is on the ground among heather, rushes, dwarf shrubs or reeds, or on a raft of floating vegetation. It is built from pieces of reed, sprigs of heather, grasses and moss, mixed with small feathers and down. A typical clutch is four to six eggs, but fewer eggs or larger numbers are not unusual. The eggs are creamy-white at first but soon become stained, and average 85 by 58 millimetres (3.3 by 2.3 in). They are mostly laid on successive days and incubationstarts after the last one is laid. The female does the incubation, which lasts about twenty-eight days, while the male remains on guard somewhere near. The chicks are precocial and able to leave the nest soon after hatching. Both parents are involved in their care and they soon learn to peck at food and become fully-fledged at eight or nine weeks, about the same time as their parents regain their ability to fly after moulting their main wing and tail feathers a month earlier. Immature birds undergo a similar moult, and move to traditional, safe locations before doing so because of their vulnerability while flightless.
In the wild
This species has a Palearctic distribution. The nominate subspecies breeds in Iceland, Norway, Sweden, Finland, the Baltic States, northern Russia, Poland, eastern Hungary and Romania. It also breeds locally in the United Kingdom, Denmark, Germany, Austria, the Czech Republic, Slovakia and Macedonia. The eastern race extends eastwards across a broad swathe of Asia to China. European birds migrate southwards to the Mediterranean region and North Africa. Asian birds migrate to Baluchistan, Azerbaijan, Iran, Pakistan, northern India, Bangladesh and eastward to China.> In North America, there are both feraldomestic geese, which are similar to greylags, and occasional vagrant greylags. Greylag geese seen in the wild in New Zealand probably originated from the escape of farmyard geese, and a similar thing has happened in Australia where feral birds are now established in the east and southeast of the country.
Greylag geese are herbivorous and feed chiefly ongrasses. Short, actively growing grass is more nutritious and greylag geese are often found grazing in pastures with sheep or cows. Because of its low nutrient status, they need to feed for much of their time; the herbage passes rapidly through the gut and is voided frequently. The tubers of sea clubrush(Bolboschoenus maritimus) are also taken as well as berries and water plants such as duckweed (Lemna) and floating sweetgrass (Glyceria fluitans). In wintertime they eat grass and leaves but also glean grain on cereal stubbles and sometimes feed on growing crops, especially during the night. They have been known to feed on oats, wheat, barley, buckwheat, lentils, peas and root crops. Acorns are sometimes consumed, and on the coast, seagrass (Zostera sp.) may be eaten. In the 1920s in Britain, the pink-footed goose “discovered” that potatoes were edible and started feeding on waste potatoes. The greylag followed suit in the 1940s and now regularly searches for tubers on ploughed fields.