|Geese are waterfowl belonging to the tribe Anserini
of the family Anatidae. This tribe comprises the genera
Anser (bird) (the grey geese), Branta (the black
geese) and Chen (the white geese). A number of other
birds, mostly related to the shelducks,
have "goose" as part of their name. More distantly
related members of the Anatidae family are swans, most
of which are larger than true geese, and ducks, which are smaller.
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 to 5 °C 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 2.54.1 kg weight, and the smallest is
the Ross's Goose at 1.21.6 kg . 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 primaryand
also often secondaryremiges (pinions). The closely related
"black" geese in the genus Branta differ in
having black legs, and generally darker body plumage.
The black geese of the genus Branta are waterfowl belonging
to the true geese and swans subfamily Anserinae. They
occur in the northern coastal regions of the Palearctic and
all over North America, migrating
to more southernly coasts in winter, and as resident birds in
the Hawaiian Islands. Alone in the Southern Hemisphere, a self-sustaining
feral population derived from introduced birds of one species
is also found in New Zealand.
The black geese derive their vernacular name for the prominent
areas of black coloration found in all species. They can be
distinguished from all other true geese by their legs and feet,
which are black or very dark grey. Furthermore, they have black
bills and large areas of black on the head and neck, with white
(ochre in one species) markings that can be used to tell apart
most species.[note 1] As with most geese, their undertail and
uppertail coverts are white. They are also on average smaller
than other geese, though some very large taxa are known, which
rival the Swan Goose and the Black-necked Swan in size.
The Eurasian species of black geese have a more coastal distribution
compared to the grey geese which share the same general area
of occurrence, not being found far inland even in winter (except
for occasional stray birds or individuals escaped from captivity).
This does not hold true for the American and Pacific species,
in whose ranges grey geese are for the most part absent.