You might think large white geese really can't be that difficult to identify. This is reasonably true until you find a solitary
Snow Goose (Chen caerulescens) grazing in some far off pasture, or spot a lone
Ross's Goose (Chen rossii) swimming in a reservoir. Their identifying features only a haze in the distance. Occasionally you might find a mixed flock and the differences become clear since one is obviously larger than the other. When the two are conveniently found together, such as the two in these photos, you tell yourself you will never make the mistake of confusing these geese again.
Both look very much the same from a distance- white geese with black primaries in their common "white morph" phase. A closer look reveals the structural difference between them. Snow Goose (or "Lesser Snow Goose" representing the interior west, and C.c.
atlantica or "Greater Snow Goose" being found in the east) is a larger bird- longer necked, longer legged with a bigger head. Superficially similar,
Ross's Goose, the smallest white goose, looks like a smaller, dumpier version of it's larger relative. Comparisons of overall body size, neck length, bill size and shape all help to distinguish the two species. Each has a "blue morph" phase, but Snow Goose maintains a white head while
Ross's Goose looks somewhat like a
Barnacle Goose (Branta leucopsis) in this form
.At close range one of the best field marks for separating these two is the shape of the head and bill. Snow Goose shows a longer wedge-shaped head. It has a larger reddish-pink bill with black cutting edges that form "lips", or what is commonly referred to as a "grin patch."
Ross's Goose by contrast lacks this feature. These black "lips" on the sides of the mandibles of Snow Goose can be seen from quite some distance away with binoculars or a spotting scope and help to identify this goose to species. In comparison
Ross's Goose has a smaller rounded head, and a stubby pinkish bill. It lacks the grin patch of its larger counterpart.
Snow Goose illustrating the larger bill and black "grin patch"
Ross's Goose illustrating the short, stubby bill. Note warty area at base
Another helpful feature at close range in separating Ross's from Snow is the warty area at the base of the upper mandible. This warty area is occasionally bluish-gray in color and is most apparent in older males. Madge and Burn (1988) note such warty protuberances are considered to be a useful isolation character that prevents extensive hybridization where the two species breed alongside each other.
Speaking of hybrids, this helpful little exercise wouldn't be complete without a cautionary note on hybrid geese. These two are known to hybridize where their breeding territories overlap in the Arctic north. A particular goose showing characters of both species may in fact be a hybrid. Such birds are probably best left as unidentified, but do make for interesting study.
So who was Ross and why is a goose named after him? Ross's Goose is named in honor of Bernard Rogan Ross (1827-1874) by John Cassin, curator of birds at the Philadelphia Academy of Natural Sciences. Ross was the chief trader for the Hudson Bay Company in the MacKenzie River District in northwest Canada during the 1860's. Ross's primary significance is in the field of natural history rather than the fur trade. Like many company men he contributed much to the early scientific knowledge of the northwest. While at Fort Simpson he made valuable collections of mammals, insects, and birds, forwarding specimens to the Smithsonian Institution in Washington, the Royal Scottish Museum in Edinburgh, and the British Museum in London. Ross's Goose was named in his honor in 1861.
These photographs were taken on November 24, 2007 at Waller County Park in Santa Maria, Santa Barbara County, California. Photos © J. Chavez
