The Snow Goose, Anser caerulescens, is a North American waterfowl species. These geese breed in the Arctic tundra and migrate across the continent, often gathering in agricultural fields during the winter. Identifying this species can be complex due to significant variation in plumage color. This variation involves distinct genetic color phases, known as morphs, which result in individuals appearing entirely white or predominantly dark gray.
Shared Identification Traits
Regardless of their overall color, all adult Snow Geese share a set of physical features important for accurate identification. The most distinctive trait is the presence of jet-black primary feathers, or wingtips, which contrast sharply with the rest of the wing plumage. These black feathers are clearly visible when the bird is in flight, but they can also be noticed when the goose is resting on the ground.
The bill is typically rose-red or bright pink in adult birds. Along the cutting edge of the mandibles, a dark, black line is visible, creating what is known as the “grinning patch.” This dark line is a reliable field mark that helps distinguish it from the closely related Ross’s Goose. The Snow Goose is a medium-sized goose, measuring between 25 and 31 inches in length, with a thick neck and a hefty, triangular bill structure.
Understanding the Color Morphs
The variation within the species is due to color polymorphism, where two distinct color phases, or morphs, exist and interbreed freely. These two phases are commonly referred to as the White Morph and the Blue Morph. The White Morph, which gave the species its name, is characterized by bright, clean white plumage covering nearly the entire body.
In this phase, only the primary wing feathers are black, creating a high-contrast look when the bird is seen flying overhead. The head of a white morph may sometimes appear stained rusty-orange, which is not a natural pigment but a discoloration caused by feeding in iron-rich soil.
The Blue Morph, once mistakenly considered a separate species, exhibits a body, breast, and flanks that are a deep slate-gray or brownish-gray. Despite the dark body, the Blue Morph maintains a highly contrasting white head and upper neck. Both morphs share the pink bill with the dark grinning patch and the pink legs and feet. The Blue Morph also has white under-tail coverts and white armpits, which help distinguish it from other dark goose species.
Distinguishing Juveniles from Adults
Age is another factor that affects the appearance of the Snow Goose, separate from the color morphs. Juvenile geese, birds in their first year of life, generally display duller, less defined plumage compared to the crisp coloration of adults. These young birds often appear mottled or washed-out gray, with their underlying adult morph not yet fully apparent.
A juvenile White Morph bird, sometimes called a “dirty bird,” has a body and wings tinged with gray-brown, lacking the pure white of its parents. For both morphs, the bill and legs are a dark or dusky gray-pink rather than the vibrant pink of an adult. The diagnostic black grinning patch is often absent or much less defined in a young bird, which may instead have a uniformly dark bill. Juvenile plumage is replaced by adult coloration during the first year, typically before the bird returns to the breeding grounds.