Snow Goose

Chen caerulescens

Snow Goose is a comparative rarity in Sonoma County, mostly recorded here as an occasional flyover or as a stray with other migrating geese that have made a stop in the county. Earliest records here are from late September. Latest records are from mid-April. Reported sporadically at Bodega Bay, Shollenberger Park/Ellis Creek Water Treatment Facility, the Bodega Farm Pond, Carmody Rd. Pond, and Hudeman Wetlands, among other locations, but records are comparatively few. Usually only a handful of birds are reported in the county each season. Breeds on far north Arctic tundra. Winters well south of us (to northern coastal Mexico), but large numbers can be seen in California inland and north of Sonoma County during migration. Commonly associates with Ross’s Goose (Chen rossii) and other geese.

A moderately sized white goose with black flight feathers. The black feathers are mostly hidden when at rest, appearing as a tuft of black at the back end of the bird, but the black on the wings is conspicuous in flight. Two subspecies are recognized--C. caerulescens atlanticus, or “Greater” Snow Goose, and C. caerulescens caerulescens, or “Lesser” Snow Goose. The larger “Greater” Snow Goose breeds further west and it is presumably these birds we see when they pass through the area. Snow Goose also has two color forms. Dark morph birds were formerly considered a separate species, known as Blue Goose. The dark form has a white head but its body is a dark slightly bluish grey-brown. These birds are fairly rare, however. Immature Snow Goose of the more common white form is greyish with grey legs and a dark bill. Adults have pink legs and a dusky pink bill. Immature birds of the Dark form are grey above and pale below with grey legs and bill. The shape of the bill is distinctive in all birds. Note the “grin patch,” a horizontally elongated dark area at the bottom edge of the bill that makes the bird look like it's smiling (photo above). In flight, the white form may be identified by the black primaries against the otherwise white body (although see notes below about distinguishing from Ross’s Goose). The dark form may be distinguished in flight from other dark geese--in Sonoma County, most likely a stray Greater White-fronted Goose (Anser albifrons)--by its two-toned underwing and pink bill and legs, if visible. Face and head may be stained yellowish or brownish in both Snow Goose and Ross’s Goose because of foraging in water, but much more commonly in the case of Snow Goose, according to the National Geographic field guides.

Most likely to be confused with Ross’s Goose. Ross’s Goose, also rare in Sonoma County, looks rather like a miniature Snow Goose. On the wing, size is the best indicator. Snow Goose is a much larger bird (about 25% larger, averaging around 30 inches head to toe), but size can be hard to judge in the case of an isolated bird on the wing. Given a good look at a standing bird, there are many useful differences besides size. Snow Goose has a somewhat square, blocky-looking head, while Ross's Goose has a distinctly rounded head. Ross’s Goose has a proportionally shorter neck than Snow Goose. Ross's Goose has a very small bill relative to its head size (usually reddish pink and often slightly greenish and warty at the base), and the line formed by the base of the bill at its point of junction with the feathered parts of the head is a fairly straight vertical line. In Snow Goose, the line is distinctly incurved in the direction of the bill tip. Ross's Goose lacks the "grin patch" often noted as diagnostic for Snow Goose. The Sibley and Peterson guides have good comparative illustrations (also see the photo of Ross’s Goose below for comparison). Juvenile Snow Goose shows much more grey than juvenile Ross's Goose, especially on the back.

Selected County sightings: Carmody Rd. Pond (October 3, 2012, Ken Wilson); Ellis Creek Water Treatment Facility (April 11, 2012, Bob Dyer); Bodega Farm Pond (January 21, 2011, Doug Shaw); Carmody Rd. Pond (October 19, 2010, Rich Stallcup)