The two white Arctic geese look very similar and are difficult to tell apart, particularly in single species flocks or as individuals. Both the snow goose (Chen caerulescens) and the Ross’s goose (Chen rossii) are white with black primaries (wing feathers) and pink legs and bills. In a mixed flock it is easier to distinguish the two species because a snow goose’s goose is about 40% larger than a Ross’s goose.
The snow goose head is longer and more wedge-shaped while the head of a Ross’s goose is shorter and more rounded. Snow geese have longer necks. Ross’s bills are shorter, more triangular and more delicate looking than the longer, more substantial bills of snow geese. Snow geese have a “grinning patch” or “black lips” meaning that there is a dark line where the mandibles meet. Because of their longer, more sturdy bills snow geese can dig deeper in the mud than the Ross’s with their petite bills. As a consequence snow geese have rusty head feathers due to staining caused by iron oxides in the water and mud. In flight a Ross’s goose has a more rapid wing beat.
Adding to the confusion, Ross’s and snow geese can hybridize with intermediate forms resulting.
With practice it becomes easier to separate Ross’s from snow geese. Leonard is quite good at identifying the two geese. Me – not so great unless I can use size in a mixed flock as an identifying trait.
Both pictures, taken at wild rice fields near Glenburn CA (Shasta County) show a snow goose in the center surrounded by Ross’s geese. The Ross’s geese are smaller (except where the camera angle distorts the perspective) while the snow geese have rusty colored head feathers. The snow goose grinning patch is also easily seen in the picture on the left.