Identification of Snow Goose and Ross’ Goose

Everything in nature has multiple connections, so in studying bird identification we don’t just look at the physical field markings of the bird in isolation. We have to think about habitat, behavior, total distribution and many other factors.

The Snow Goose is a perfect example. The challenge of identifying this species has changed intriguingly over the past few decades. It’s not that the bird looks different today; the change is driven by a huge population increase and range expansion of snow geese in general.

Snow Geese come in two color morphs: white (with black wingtips) and “blue”, with a predominantly blue-gray body and white head. The two look so different that they were classified as separate species until 1973. Identifying the “Blue Goose” form is rarely a problem, but it can be very difficult to separate the White Snow Goose from a very similar but smaller bird, the Ross’s Goose. .

At one time, the Ross’s Goose was rare and localized, breeding in a limited area of ​​north-central Canada, wintering primarily in the central valleys of California. Prior to the 1950s, its total population was estimated at only around 6,000 people. Today, it can number up to two million. Its breeding range has expanded considerably, and it can be found wintering across much of temperate North America.

So in many areas where Snow Geese could once be identified at a glance, we now have to glance to exclude Ross’s Goose. Fortunately, there are distinct differences between snow geese and typical Ross’s geese. On the Atlantic coast, in the wintering grounds of the large Snow Goose subspecies, the few Ross’s Geese present seem tiny in comparison. Farther west, the Lesser Snow Goose averages about 20% larger than Ross’s, but size alone is not enough to identify it. There it is important to study the details of the shape and pattern of the beak, as described in the captions of the photos with this column. A prominent black “smile patch” marks the Snow Goose’s large pink beak where the mandibles meet. Ross’s Goose barely shows a hint of that; its beak is small and stocky and has a two-tone appearance, mostly reddish-pink with a contrasting blue-gray base.

But there is a new complication. Both the Snow Goose and the Ross’s Goose have experienced considerable population increases and range expansions, and their breeding ranges now largely overlap. The two species often interbreed. Some studies have suggested that hybrids make up nearly five percent of the total population, although others indicate the proportion is less than two percent. Additionally, the Snow X Ross hybrids have backcrossed to the parent species, so it is now possible to see a full range of intermediates between “pure” Snow Geese and Ross’s. If one of these geese is found in an area where it would be rare, it is now necessary to study every detail to be able to identify it with certainty.

Ross’s goose, adult. February in Los Angeles County, California. Photo by Brian E. Small

Ross’s Goose’s most well-known field mark is the fact that it lacks the black “smile patch” of the Snow Goose. However, everything about the shape and color of the beak is distinctive. The Ross’s Goose has a short, stubby beak, often appearing “sunken” to the face. The beak is mostly pink, with a noticeable blue-gray patch at the base; in older birds, this blue-gray area appears quite bumpy or warty at close range. The border between the base of the beak and the feathers of the face forms a fairly straight vertical line. Additionally, the Ross’s Goose is a significantly smaller bird and has a more rounded head and shorter neck than the Snow Goose, which contributes to a softer or “cute” facial expression.

Snow goose, adult blue morph. December in Socorro County, New Mexico. Photo by Brian E. Small

The “Blue Goose” form of the Snow Goose, long considered a separate species, is distinctive in adulthood, with a white head and dark plumage. The only similar species is the Emperor Goose, an Alaskan specialty with a prominent black chin. However, there is also a very rare blue form of Ross’s Goose. The size, shape, beak shape, and beak color markers are helpful in spotting this shape. Also, their body plumage tends to be blacker than that of the Blue Snow Goose. They usually have white bellies (but lots of blue snows too). Most birds that at first look like the Blue Ross’s Goose turn out to be Snow X Ross’s Goose hybrids, so this form should be identified with caution.

Snow goose, immature white form. December in Socorro County, New Mexico. Photo by Brian E. Small

Young white-morph Snow Geese initially show much dull gray, especially on the upperparts, and their legs and beaks are blackish in early fall. Their appearance gradually changes throughout late fall, winter, and spring as the gray fades and new white feathers are molted. On many, the beak starts to turn pink in November, but the December bird in this photo clearly still has a very dark beak. Domestic geese can have a number of variations, and some have a color pattern similar to this; thus, a purported Snow Goose seen alone, away from any flock, should be carefully checked for details of beak shape, general shape, and contrasting black primaries in the wings.

Ross’s goose, immature. December in Socorro County, New Mexico. Photo by Brian E. Small

First-winter immatures of Ross’s geese and snow geese differ in size, shape, and beak shape, much like adults. This young Ross’ goose has the typical short neck, round head and short beak structure of the species. Additionally, the general plumage of young Ross is initially paler, with a much lighter and less extensive gray tint on the upperparts. This pale gray is replaced by white feathers by a gradual moult during the first season. Studies of migrating geese on the Canadian prairies have shown that the beaks of young Ross’s geese already turn pink in October, while young snow geese still have dark beaks, so the beak color shown in this photo of December is not unexpected.