As winter approaches, birders in North America will soon be confronted with the identification challenge of separating Snow Geese from Ross’s Geese. Typically this is pretty easy, but the small numbers of Snow X Ross’s goose hybrids that exist add an additional layer of difficulty.
In this photo, we have a typical Snow Goose at the back with the long neck, sloping forehead, and long bill that shows a significant “grinning patch”, the oval-shaped opening between the upper and lower mandible. The bird in the center is a typical Ross’s Goose, much smaller than the Snow Goose with a rounded head, shorter neck, and shorter bill that lacks the grinning patch. It also has the blue-gray, warty skin at the base of the bill that is typical of Ross’s Goose. What about the bird in front though? It looks a little larger, it has a longer bill than the Ross’s in the center, an intermediate head shape with a fairly straight, sloping forehead, and it looks a little larger and heavier than the Ross’s Goose, though smaller than the Snow Goose. Could this be one of the dreaded hybrids? No, this is not a hybrid. It is an (apparently) pure Ross’s Goose, but it highlights a little known fact that is relevant to the identification of this group: Ross’s Geese show significant variation in size and structure between males and females. The bird in front is an adult male whereas the center bird is an adult female. This variation between the sexes is something to consider when faced with a Ross’s Goose that doesn’t look absolutely typical.
This photo shows a Snow Goose on the left and a smallish, but very dark goose on the right. The blue color on the back and neck is much darker than is typical for a blue-morph Snow Goose, also known as a “Blue Goose”. This dark color combined with the dark cap and pattern of the scapulars point toward a “blue” Ross’s Goose, the dark-morph of the Ross’s that, unlike blue-morph Snow Goose, is extremely rare. While I’m not 100% sure, I called it a probable blue-morph Snow X Ross’s Goose hybrid, not a Blue Ross’s Goose, because it was about 85% as large as the surrounding Snow Geese and the bill looked intermediate. While hybrids are not particularly common, they are something to be aware of and they do muddy the waters when attempting to separate Snow Goose from Ross’s.
The final photo is a cool photo of an intermediate-morph Snow Goose in flight, but look at the birds in the background. There are two gray-mottled first-cycle Snow Geese, but the tight flock of four farther back is a family group of Ross’s Geese. The short bills of two of the members of the flock can be seen well.
Cameron Cox currently leads photographic birding tours all over the world. To learn more about these tours or to sign-up for one, please visit the Tropical Birding website.