(
Anser caerulescens) in
Quebec,
Canada (
Anser cygnoides domesticus), the domesticated form of the
swan goose (
Anser cygnoides) (
Branta leucopsis) in
Naantali,
Finland The two living
genera of true geese are:
Anser, grey geese and white geese, such as the
greylag goose and
snow goose, and
Branta, black geese, such as the
Canada goose. Two genera of geese are only tentatively placed in the Anserinae; they may belong to the
shelducks or form a subfamily on their own:
Cereopsis, the Cape Barren goose, and
Cnemiornis, the prehistoric
New Zealand goose. Either these or, more probably, the goose-like
coscoroba swan is the closest living relative of the true geese.
Fossils of true geese are hard to assign to genus; all that can be said is that their fossil record, particularly in
North America, is dense and comprehensively documents many different species of true geese that have been around since about 10
million years ago in the
Miocene. The aptly named
Anser atavus (meaning "progenitor goose") from some 12 million years ago had even more
plesiomorphies in common with swans. In addition, some goose-like birds are known from
subfossil remains found on the
Hawaiian Islands. Geese are
monogamous, living in permanent pairs throughout the year; however, unlike most other permanently monogamous animals, they are territorial only during the short nesting season. Paired geese are more dominant and feed more, two factors that result in more young. == Fossil record ==