San Diego Natural History Museum--Your Nature Connection[San Diego County Bird Atlas Project]

Focus On...

the Snow and Ross' Geese

Long ago, in the 19th century, geese of several species were common, even abundant, in winter along the coast of southern California. Canada, White-fronted, Snow, or Brant, hunters shot what they could and sold them in the markets. Those were the days of the Gold Rush, the Wild West, and the idea that man could exhaust the production of the planet had hardly entered human consciousness. For large birds though, easily seen and highly concentrated in flocks, the collapse came quickly. By 1895 the editor of a Santa Ana newspaper was complaining that four hunters from Los Angeles could get "only" 900 geese in two days. By 1919 Frank Stephens wrote that all of San Diego County's geese were common only formerly. Decades passed in which the Snow Goose was only a rare visitor to San Diego County. The survivors regrouped their winter range in new habitat in the Imperial Valley, gradually rebuilding their numbers in a refuge managed for them. As the Snow Goose increased at the Salton Sea National Wildlife Refuge, its sister species, Ross' Goose, made an appearance, extending its winter range south from California's Central Valley, then gradually increasing until today it may make up as much as one third of the Salton Sea's flocks of white geese.

With the arrival--or return--of Ross' Goose in southern California, birders now face an identification problem with every sighting of a white goose. When adult, the plumage of the two species is identical, white with black primaries. The young birds differ somewhat, the grayish clouding on the plumage of the juvenile Snow Goose being darker and more extensive than that of the juvenile Ross'. Both species molt out of juvenile plumage mainly in their winter range, becoming mostly or entirely white by the end of the winter.

Sketch of Ross' Goose by Nicole Perretta                     Sketch of Snow Goose by Nicole Perretta

The difference in size between the two species is substantial: in weight, Ross' Goose averages about 67%, in wing length about 90%, of the figures for the Lesser Snow Goose, the only subspecies of the Snow Goose that reaches California. Nevertheless, there is appreciable individual variation and sexual dimorphism within each species, and the difference in size may be difficult to evaluate if no other birds are nearby to afford an appropriate comparison. The Ross' Goose is almost exactly the same size as a male Mallard, though, and because it so often shows up where Mallards are around, this parallel is often useful.

The most conclusive difference between the two species is in the bill--size, shape, and pattern. The Snow Goose's bill is longer (at least 50 mm), has black "lips" along the sides, and lacks any warty growths at the base. The Ross' Goose's bill is shorter (no more than 46 mm) but just as deep at the base, giving the bill a conspicuously blunter shape. Black lips are very narrow or invisible. As a Ross' Goose ages, it grows olive-gray warts over the base of the bill, unique to this species. The birds display these warts prominently when they confront each other, suggesting the warts serve to advertise their bearer's status. Young birds of both species have smooth gray bills that gradually turn bright pink.

The shorter bill of the Ross' Goose, in combination with its shorter neck and smaller total size, serves to accentuate the roundness of the head and to give the bird a distinctive shape, probably the easiest clue to the bird's identification when seen at a distance.

The blue phase of the Snow Goose, once thought a distinct species, winters mainly in the central U.S. and reaches California in only small numbers. There is only one record of the blue phase in San Diego County, Richard Webster's of an adult and two immatures at Whelan Lake (G6) from 3 December 1983 to 16 January 1984. The blue phase of the Ross' Goose is extremely rare, possibly arising only through hybridization of blue-phase Snow Geese with the Ross'. It has been seen in the Imperial Valley but not in San Diego County.

Both the Snow and Ross' have similar migration schedules in San Diego County, arriving usually in November, departing usually in early March. One Ross' Goose at Buena Vista Lagoon (H6), however, failed to migrate north in the spring of 1998 and remained there, with the domestic Mallards, continuously until its death on 12 November 2000--it is now a specimen in the museum's research collection and served as the model for Nicole Perretta's sketch of the Ross' Goose in this issue of Wrenderings.

Map of Snow Goose distribution
    Snow Goose distribution
    Black: Maximum daily count 5-11
    Dark gray: Maximum daily count 3 or 4
    Light gray: Maximum daily count 1 or 2

The current distribution of the Snow Goose in San Diego County echoes that of the Canada Goose, by and large. Often a few Snow Geese are found mixed with a flock of Canada Geese. The sites where the Snow Goose is most regular, the San Luis Rey River valley, San Pasqual Valley to Ramona, the San Dieguito Valley, Lake Henshaw, and Sweetwater Reservoir, all have regular wintering flocks of Canada Geese. Occasionally, though, Snow Geese show up at scattered, unexpected locations, such as Paulette Ache's two in Borrego Springs (G24) on 15 January 1999, Rich and Susan Breisch's two at the northeast corner of Lake Morena (S22) on 5 December 1999, and Frank Unmack's two at Jacumba (U28) from 1 to 5 February 2000. Notice how frequently the birds are seen in pairs even when not with a flock-in the Snow Goose, mated pairs remain together for life, even in their winter range. The Snow Goose has a completely vegetarian diet of tender plants uprooted or clipped, from either shallow water or the bare ground. In much of their winter range Snow Geese feed in agricultural fields, but with the passing of grain-growing from San Diego County the birds are seen more and more in pastures and on lawns.

Map of Ross' goose distribution
    Ross' Goose distribution
    Black: Maximum daily count 22
    Light gray: Maximum daily count 1 or 2

The distribution of Ross' Goose in San Diego County shows both similarities to and differences from that of the Snow Goose. The map reveals that the Ross' often shows up in the same regions as the Snow: the San Luis Rey River valley from Oceanside to Bonsall, the San Pasqual Valley/Ramona region, and now Sweetwater Reservoir, where Pete Famolaro found one wintering this year beginning on 12 December 2001. Similarly, there are a few scattered records east of the coastal plain, in the Borrego Valley and at Lake Morena and Campo. Whereas Snow Geese often show up in San Diego County in small flocks, our records of Ross' Geese are almost entirely of single birds or pairs only. From 1979 to 1988 flocks of up to 11 were seen occasionally at Whelan Lake, but the one sighting of more than two during the atlas period was the remarkable flock of 22 Pete Ginsburg counted in Bonsall (E8) on 25 February 2000. Because Pete had seen only a single Ross' Goose at this spot earlier in the winter, we may infer these birds were spring migrants on their way north from some wintering site still unknown.

Ross' Goose also differs from the Snow in its habitat selection. Ross' occurs more often on small bodies of water with little but lawns nearby for foraging habitat-the same places where released domestic Mallards accumulate. Buena Vista Lagoon, Santee Lakes, by the Hilton Hotel at the southeast corner of Mission Bay, North Island Naval Air Station--sites of recent Ross' Geese in San Diego County hardly evoke an image of wilderness. The smaller species seems to be adapting to the urban environment better than the larger.

It is likely that Ross' Goose once occurred with the Snow Goose in San Diego County but was overlooked in the early days. Indeed, Ross' Goose was not formally distinguished as a species until 1861. In 1912 George Willett wrote that he had "seen many of these birds in the Los Angeles markets, brought in from the surrounding country," in the days when the once vast grasslands of the Los Angeles basin were a major center for wintering geese. But he reported no specific location for Ross' Goose south of Orange County. By 1931 the species' total population was estimated at only 5000 to 6000 individuals, and significant recovery did not begin until the 1950s, when the birds in the Central Valley shifted from wintering in native grassland to agricultural fields. The first record of Ross' Goose in San Diego County was in 1966, in Nestor (V11) at a pond now filled in. Now, the population in the main breeding range, the Queen Maud Gulf Migratory Bird Sanctuary on the arctic coast of Canada, is estimated at over 188,000 birds, and the species' frequency in San Diego County has risen to about five individuals per year. One can easily envision a future in which Ross' Goose becomes a common winter visitor to parks and golf courses, provided society continues to devote imported water to such extravagances, and that chemicals used to maintain them do not poison the birds.

Focus On ... | Spring 2002 Wrenderings | Bird Atlas Introduction