20111219_1499-1 - Snow Goose (Anser caerulescens atlantica)
The white geese are a small group of waterfowl which are united in the genus or subgenus Chen, in the true geese and swan subfamily Anserinae. They breed on subarctic areas of North America and around the Bering Strait, migrating south in winter. Many authorities place these species in the grey goose genus Anser. Indeed, Chen and Anser are anatomically indistinguishable. However, external morphology, biogeography, and molecular data suggest that the white geese are indeed an evolutionary lineage distinct from the grey geese ? from which they split off fairly recently, essentially replacing them in North America. The AOU recognizes this genus as distinct; most other authorities today consider it a subgenus of Anser. Like grey but unlike the Branta black geese, their feet and legs are colored in reddish hues. The bill is also reddish in these birds as in most grey geese, except in adult males of Ross’s Goose which have a blue-black grainy cere. The wingtips are black, as in all true geese, whereas the head is always white without any markings or pattern in adult birds of this genus, which distinguishes them from all other true geese except feral domesticated geese. The rest of the plumage is either white all over, or colored in various dark bluish-grey hues; the latter birds, uniquely among true geese, do not have white uppertail and undertail coverts, though the tail itself may be white. White-phase snow geese of both species can be told apart from feral geese best by the more slender, elegant neck, which is thick-set in domestic geese; these also have a generally heavier body and often lack black wingtips.
The Lesser Snow Goose Chen caerulescens caerulescens has two different appearances, white phase and blue phase. The plumage of white-phase geese is almost completely white, except for black wing tips. The blue-phase goose has a white head, a bluish colour on the feathers of the lower back and flanks, and a body that ranges in colour from very pale, almost white, to very dark. Both the white- and blue-phase snow geese frequently have rusty orange faces, because their feathers have been stained by iron in the earth where the birds feed.
The goslings of the white-phase geese are yellow, those of the blue phase nearly black. By two months of age the young birds of both colour phases are grey with black wing tips, although the immature blue-phase birds are generally a darker grey and have some light feathers on the chin and throat, which can become stained like those of the adults. The goslings are still grey the following spring; in April and May they show white scapulars, or feathers close to where the wing joins the body, white necks, and white secondary coverts, or feathers covering the base of the flight feathers. They still have an overall grey wash.
By the spring the black to dark grey bills of the immature birds have become grey-pink. The bill of the adult is pink and is narrower than the broad, black bill of the Canada Goose. It has evolved to enable the geese to eat the nutritious roots of marshland plants. The serrated edge of the bill makes the bird appear to be smiling and is sometimes called the “grinning patch.”
The Lesser Snow Goose has a wingspan of about 90 cm and its average weight is 2.2 to 2.7 kg, the male being larger.
There are two other types of white geese found in North America: the Greater Snow Goose Chen caerulescens atlantica, and Ross’ Goose Chen rossii. The Greater Snow Goose is slightly larger than the Lesser Snow Goose and nests farther north and east; blue-phase Greaters are rarely seen. The Ross’ Goose is much smaller than the Lesser Snow Goose and does not have a grinning patch on the side of the bill. Blue-phase Ross’ Geese are rare. As the numbers and ranges of both species have increased during the last 50 years, hybrids between them have become quite frequent. The hybrids are intermediate in size between Ross’ Geese and Lesser Snow Geese.