The waterfowl genus Anser includes all grey geese and sometimes the white geese. It belongs to the true geese and swan subfamily (Anserinae). The genus has a Holarctic distribution, with at least one species breeding in any open, wet habitats in the subarctic and cool temperate regions of the Northern Hemisphere in summer. Some also breed further south, reaching into warm temperate regions. They mostly migrate south in winter, typically to regions in the temperate zone between the January 0 °C (32 °F) to 5 °C (41 °F) isotherms.
The genus contains ten living species, which span nearly the whole range of true goose shapes and sizes. The largest is the Greylag Goose at 2.5–4.1 kg (5.5–9.0 lb) weight, and the smallest is the Ross's Goose at 1.2–1.6 kg (2.6–3.5 lb). All have legs and feet that are pink, or orange, and bills that are pink, orange, or black. All have white under- and upper-tail coverts, and several have some extent of white on their heads. The neck, body and wings are grey or white, with black or blackish primary—and also often secondary—remiges (pinions). The closely related "black" geese in the genus Branta differ in having black legs, and generally darker body plumage.
Read more about Anser (bird): Relationship With Humans and Conservation Status
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