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Nov 12 2011

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Snow Goose (Anser caerulescens)


Snow Goose

[order] ANSERIFORMES | [family] Anatidae | [latin] Anser caerulescens | [authority] Linnaeus, 1758 | [UK] Snow Goose | [FR] Oie de neiges | [DE] Schneegans | [ES] Ganso Azul | [NL] Sneeuwgans

Subspecies

Monotypic species

Genus

The white geese are a small group of waterfowl which are united in the genus or subgenus Chen, in the true geese and swan subfamily Anserinae. They breed on subarctic areas of North America and around the Bering Strait, migrating south in winter. Many authorities place these species in the grey goose genus Anser. Indeed, Chen and Anser are anatomically indistinguishable. However, external morphology, biogeography, and molecular data suggest that the white geese are indeed an evolutionary lineage distinct from the grey geese ? from which they split off fairly recently, essentially replacing them in North America. The AOU recognizes this genus as distinct; most other authorities today consider it a subgenus of Anser. Like grey but unlike the Branta black geese, their feet and legs are colored in reddish hues. The bill is also reddish in these birds as in most grey geese, except in adult males of Ross’s Goose which have a blue-black grainy cere. The wingtips are black, as in all true geese, whereas the head is always white without any markings or pattern in adult birds of this genus, which distinguishes them from all other true geese except feral domesticated geese. The rest of the plumage is either white all over, or colored in various dark bluish-grey hues; the latter birds, uniquely among true geese, do not have white uppertail and undertail coverts, though the tail itself may be white. White-phase snow geese of both species can be told apart from feral geese best by the more slender, elegant neck, which is thick-set in domestic geese; these also have a generally heavier body and often lack black wingtips.

Physical charateristics

The Lesser Snow Goose Chen caerulescens caerulescens has two different appearances, white phase and blue phase. The plumage of white-phase geese is almost completely white, except for black wing tips. The blue-phase goose has a white head, a bluish colour on the feathers of the lower back and flanks, and a body that ranges in colour from very pale, almost white, to very dark. Both the white- and blue-phase snow geese frequently have rusty orange faces, because their feathers have been stained by iron in the earth where the birds feed.

The goslings of the white-phase geese are yellow, those of the blue phase nearly black. By two months of age the young birds of both colour phases are grey with black wing tips, although the immature blue-phase birds are generally a darker grey and have some light feathers on the chin and throat, which can become stained like those of the adults. The goslings are still grey the following spring; in April and May they show white scapulars, or feathers close to where the wing joins the body, white necks, and white secondary coverts, or feathers covering the base of the flight feathers. They still have an overall grey wash.

By the spring the black to dark grey bills of the immature birds have become grey-pink. The bill of the adult is pink and is narrower than the broad, black bill of the Canada Goose. It has evolved to enable the geese to eat the nutritious roots of marshland plants. The serrated edge of the bill makes the bird appear to be smiling and is sometimes called the “grinning patch.”

The Lesser Snow Goose has a wingspan of about 90 cm and its average weight is 2.2 to 2.7 kg, the male being larger.

There are two other types of white geese found in North America: the Greater Snow Goose Chen caerulescens atlantica, and Ross’ Goose Chen rossii. The Greater Snow Goose is slightly larger than the Lesser Snow Goose and nests farther north and east; blue-phase Greaters are rarely seen. The Ross’ Goose is much smaller than the Lesser Snow Goose and does not have a grinning patch on the side of the bill. Blue-phase Ross’ Geese are rare. As the numbers and ranges of both species have increased during the last 50 years, hybrids between them have become quite frequent. The hybrids are intermediate in size between Ross’ Geese and Lesser Snow Geese.

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wingspan min.: 133 cm wingspan max.: 156 cm
size min.: 65 cm size max.: 75 cm
incubation min.: 23 days incubation max.: 25 days
fledging min.: 45 days fledging max.: 25 days
broods: 1   eggs min.: 5  
      eggs max.: 7  

Range

North America : North

Habitat

They nest on low grassy tundra plains and broad shallow rivers near the coast, and on islands within shallow inland lakes. Their winter grounbds are also interior agricultural lands where corn, rice, and pasture grasses provide abundant food supplies.

Reproduction

Lesser Snow Geese, unlike most other waterfowl, usually nest close to each other in large colonies with densities of up to 2 000 pairs per square kilometre. When snow geese first return to their breeding colony the ground is often still snow-covered. But snow geese are well adapted to wait for the thaw of ice and snow in order to nest. In spring they carry heavy loads of fat and protein in their body reserves and can live on these for up to two weeks, though where possible they feed on emerging vegetation. As the snow begins to melt, the flock breaks into smaller groups and eventually into pairs.

Nesting starts as early as northern snow conditions allow and varies between colonies. Depending on latitude, egg-laying begins from late May to mid-June. If delayed by snow cover after June 20, the geese do not breed; instead, they resorb their eggs and wait until the next year.

The nest itself consists of a scrape in the moss or gravel that often becomes built up into a mound over the years with bits of moss, willow, and grasses. Some down, or fine feathers, is added to the nest bowl as the eggs are laid. From two to six eggs are produced, with the average clutch size being around four. Incubation, or sitting on the nest to keep the eggs warm until they hatch, begins when the last egg is laid and continues for about 23 days. The lapse of time varies according to the number of eggs produced, and peak hatching occurs between late June and mid-July. Eggs in the more southern colonies generally hatch earlier than those in the north.

Only the female incubates. The male remains nearby to protect the female and nest from predators and from other geese looking for a ready-made home. The female leaves the nest for only a few minutes each day, and in the latter part of the incubation period she may not leave at all. As a result she is very thin by the time hatching begins; she may lose up to 30 percent of her body weight, which she regains when she starts to feed with the goslings.

After all the young birds have hatched they may stay together in the nest for up to 24 hours. When they have dried off they leave the nest, together with both parents, and begin to feed. The young geese must grow very quickly in order to be large enough to fly south before the Arctic winter returns. Initially their diet consists mostly of insects, which are never scarce during summer in the Arctic. As they grow, their need for a high-protein diet diminishes, and within about two weeks they have switched almost completely to grasses and sedges.

From an initial weight of about 100 g at hatch the young grow to more than 1 200 g in six to seven weeks. While the young are still small both adults moult, or shed, their flight feathers, the males a week or so ahead of the females. Subadults and failed breeders moult two to three weeks before successful parents. Some goslings and their parents walk and swim up to 50 km during the eight-week period from hatching to fledging, or first flight. Both the young and the adults must spend most of their time feeding in order to grow large enough to fly or to regain their flight feathers by mid-August. The family group gains its power of flight at the same time.

Snow geese show a very strong family bond. The young and adults remain together throughout the winter and the spring and fall migrations. The family generally breaks up when the parents start a new nest; however, sometimes the young of the previous year rejoin the new family.

Feeding habits

On its Arctic breeding grounds the Lesser Snow Goose feeds on grasses and sedges. On migration, pasture grasses, corn, and wheat increasingly form the main part of the diet, although birds migrating along the west coast still rely on traditional estuarine plants. During the winter on the Fraser River delta, the geese also feed on pasture grasses and fall rye. In wintering areas along the Gulf of Mexico, the birds have traditionally fed on tubers, roots, and grasses in coastal marshes; however, in about 1960, some of this wintering population began to feed farther inland on cultivated grain-both on fall-sown crops and on the waste grain left by bigger harvesting equipment. In spring, Lesser Snow Geese puts on much weight by feeding voraciously on grasses, weeds, forbs, and waste grain.

Initially the goslings, or young, feed mainly on insects, which are plentiful during summer in the Arctic. As they grow, their need for a high-protein diet diminishes, and within about two weeks they have switched almost completely to grasses and sedges.

Video Snow Goose

copyright: J. del Hoyo


Conservation

This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Surprisingly, in an age of declining wildlife populations, Lesser Snow Geese have doubled in number since the mid-1970s, and among North American geese, their numbers are second only to those of the Canada Goose. However, because there are many subspecies and races of Canada Geese, the Lesser Snow Goose can probably be considered the single most abundant goose in Canada. Currently, about 2 000 000 nest in Canada, along the coast of Hudson Bay, from Cape Henrietta Maria in Ontario to Keewatin; on Southampton Island and on southern Baffin Island, Nunavut, and in northern Mackenzie and Keewatin south of Queen Maud Gulf, Nunavut; and on Banks Island in the Northwest Territories. The other major concentration of breeding Lesser Snow Geese in the world is the one on Wrangel Island in eastern Siberia, where there are now about 100 000 birds.

Although most Lesser Snow Geese nest in Canada, only 20 000 to 40 000 winter in this country-in south-coastal British Columbia-and they originate on Wrangel Island. Birds nesting in the Canadian Arctic winter in central California, New Mexico, the interior highlands of Mexico, and along the Gulf of Mexico, both on the coast and, increasingly, in inland areas
Snow Goose status Least Concern

Migration

Because Lesser Snow Geese breeding in Canada are spread over such a vast area, they take many different routes between their breeding and wintering areas. Lesser Snow Geese breeding in the western Arctic form pre-migration staging flocks in the Mackenzie River delta and along the north coast of Yukon and Alaska. On migration they fly up the Mackenzie River, through Alberta and western Saskatchewan and on to central California or the interior of Mexico.

Birds from the eastern Arctic stage in very large numbers in James Bay and on the west coast of Hudson Bay before heading farther south. During migration they pass through Manitoba and Ontario, on a rather broad front, en route to the coast of the Gulf of Mexico.

Major shifts in autumn distribution have taken place in prairie Canada since 1975. In that year 50 000 to 100 000 Lesser Snow Geese started to use a more westerly route through eastern Saskatchewan. The shift from southwestern Manitoba to eastern Saskatchewan continued in subsequent years. This means that birds from the central Arctic fly in two directions: one southwestward corridor takes them into Alberta and western Saskatchewan; another southeastward corridor goes through southern Manitoba.

Birds from Wrangel Island in Siberia fly across the Bering Strait to Alaska and down the west coast of British Columbia to major wintering areas on the Fraser River, the Skagit River in Washington, and in central California. Some, also bound for California, fly up the Mackenzie River and through Alberta.

We know less about the spring migration routes, which appear to be similar to those in fall, but with some shifts between corridors. Birds returning to Wrangel Island tend to fly along the British Columbia coast, but some of the Wrangel Island population also uses an interior route through Montana, Alberta, Saskatchewan, Northwest Territories, and interior Alaska. Birds of western Canadian origin wintering in California fly north through Alberta, then down the Mackenzie valley to the western Arctic coast. Birds returning from the coast of the Gulf of Mexico fly up the Mississippi and Missouri river valleys to an important staging area southwest of Winnipeg and then in a more-or-less straight northeasterly line to James Bay and the Hudson Bay coast and north into the eastern Arctic.

Distribution map

Snow Goose distribution range map

Literature

Title The impact of goose grazing on arctic and temperate wetlands
Author(s): Gilles Gauthier, Jean-Francois Giroux, Line Rochefort
Abstract: Geese are large, herbivorous birds that graze in h..[more]..
Source: Acta Zoologica Sinica 52(Supplement): 108-111, 2006

download full text (pdf)

Title Comparative energy budgets of Greater Snow Geese Chen caerulescens atlantica staging in two habitats in spring
Author(s): Bedard J. & Gauthier G
Abstract: During a recent population increase, the high-arct..[more]..
Source: ARDEA 77 (1): 3-20.

download full text (pdf)

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