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.