Oie de Ross

Identification

Ross's goose have a rounded head above a short neck. The bill is short and triangular, and has a bluish base with warty structures that increase in prominence with age. Adults are identified by all-white secondary feathers, while juveniles' will be dark centered. Females average 6% smaller than males. Legs will begin as olive gray on goslings and turn deep red as they mature.<p>There is no geographic variation or identified subspecies. Related species include other Anser geese, particularly the lesser snow goose, where the two mtDNA lineages imply frequent hybridization. Two hypotheses about the evolution of Ross's goose are that they arose from a population of snow geese that were isolated by glacial advance or in a refugium that remained ice free.<p>Measurements:[citation needed]

Taxonomie

Ross's geese, along with other "white geese" (i.e., snow goose, emperor goose) previously belonged to the genus Chen, however, recent genetic sequencing has concluded that this genus was polyphyletic with the Anser genus, where most taxonomists now place Ross's goose and its allies. <p>Members of the Chen genus were officially transferred to Anser in the International Ornithological Committee's World Bird List version 6.3 in 2016.

Nom scientifique

Anser rossii

Autorité

Cassin, 1861

Ordre

Ansériformes

Famille

Anatidae

Genre

Anser

Répartition et habitat

Landscape in the central Arctic is dominated by flat plains with some rock outcrops and drumlins, wet meadows, and marshy tundra. Vegetation includes patches of dwarf birch, willow, grasses, sedges, and low-growing vascular plants including crowberry, lapland rosebay, and lousewort. Large colonies of nesting birds can cause extensive damage to plants by overgrazing.

Aire de reproduction

NA : n Canada

Aire hors reproduction

s, w USA and n Mexico

Migration

Complete migrants

Comportement

Ross's geese form large nesting colonies on islands in shallow lakes and adjacent mainland, building nests on the ground made of twigs, leaves, grass, moss, and down. Females lay an average of 4 eggs per clutch and incubate the nest for 21–23 days.<p>A study of ground-based sampling along the McConnell River on the west coast of Hudson Bay reported a population of about 81,000 nesting Ross's geese.<p>These birds migrate from their Canadian nesting grounds by mid-October, probably in response to limited food before freezing temperatures set in, and begin their return in mid-April to May.<p>Like most geese, they are grazers that feed on grasses, sedges, and small grains. They often forage in large mixed flocks with snow geese.<p>

Conservation

Tendance de la population

rising