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Tucson Audubon Society
Dastardly Duos
Snow Goose and Ross's
Goose
by Larry Liese
Illustrations by George C. West
(Article first appeared in the February
2001 Vermilion Flycatcher newsletter. To receive the newsletter in
the mail, become a member of the Friends of
Tucson Audubon.)
Winter is still with us, although it’s 70 degrees as I write this (Ah - life in southeastern Arizona!), and one of the avian delights we get to view in winter is an occasional goose. Four species of geese regularly occur here, but only two give us initial confusion in determining what they might be: the uncommon (Lesser) Snow Goose and the rare Ross’s Goose were traditionally considered difficult to separate but in reality are straightforward once one knows which field marks to observe. The Canada Goose and the Greater White-fronted Goose present no problems in identification.
From a large
distance, size starts the identification process rolling. These geese
occur together frequently, with Snow Geese usually outnumbering the
Ross’s Geese. The Ross’s weigh more than one-third less and are about
20% shorter than the Snows, though it is easy to get into trouble with
these facts when viewing a solitary bird. In a mixed group, the size
difference really shows up.
Plummages of these two species are nearly identical in adult birds.
Besides size, the key field mark differences are in the head, bill, and neck shape. At intermediate distances, the Snow Goose shows a flatter head and a much longer bill, along with a longer neck. However, when one gets a close view, the differences in the bill show up strongly. The Ross’s Goose has a short stubby bill, with bluish/gray, warty protruberances or caruncles at the base. The effect is a band around the base of the bill contrasting with the pink color of the rest of the bill. The border at the base of the bill is straight and vertical. The much longer bill of the Snow Goose shows the well-known grin patch or grin line, which is a thick black horizontal line where bill halves come together. The border between the bill and feathers on the bird’s face is strongly curved.
An effect of the flatter head of the Snow Goose is that the eye appears very close to the bird’s forehead. On the Ross’s Goose, the head is rounder with the eye more centrally located in the bird’s face, giving it a gentle look. Also, note that the Ross’s Goose has a steeper sloping forehead. The head of the Snow Goose occasionally has rusty-orange stains reportedly resulting from grubbing in sediment or mud containing iron oxides. For some reason, this does not usually occur in Ross’s Geese.
So, the next time one of these two comes your way when out birding, don’t let your goose get cooked. Zoom in on these traits and come away a winner!
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This page was updated on 02/21/06