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Geese Of North America

The six species of goose that breed in North America are the Canada goose (Branta canadensis), brant ( B. bernicla ), black brant (B. nigricans), snow goose (Chen caerulescens), Ross's goose (C. rossii), and white-fronted goose (Anser albifrons). Two other Eurasian species are occasionally seen during winter: the barnacle goose ( B. leucopsis ) on the northeastern coast, and the emperor goose ( Philacte canagica ) along the Alaskan coast. The two most abundant species of geese in North America are the Canada goose and the snow goose. The Canada goose is also known as the "honker" because of its resonant call, given especially enthusiastically during migratory flights and while staging. Because of geographic variations in size, morphology, and color patterns, the Canada goose has been divided into about 11 races. However, these races intergrade with each other, and should best be considered to represent continuous, geographic variations of a genetically polymorphic species. The largest race is the giant Canada goose (B. c. maxima), of which mature ganders typically weigh about 12.5 lb (5.7 kg). The giant Canada goose has become rather common in some urban and suburban areas, where it has been widely introduced and has established feral, non-migratory, breeding populations. However, because of past overhunting, this race is much less abundant than it used to be in its natural breeding range of southern Manitoba, northwestern Ontario, and Minnesota. The smallest race is the cackling Canada goose (B. c. minima). Males of this rather dark goose only weigh about 3.5 lb (1.5 kg). This relatively abundant race breeds in the western subarctic, especially in Alaska, and winters in the Pacific Northwest of the United States and southwestern British Columbia.

Because of its abundance and widespread migrations, the Canada goose is probably the most familiar goose to most North Americans. During their migrations, the larger-sized races of Canada goose tend to occur in relatively small, often family-sized flocks, and their calls tend to be extended, sonorous honks. Smaller-bodied races flock in much larger groups, ranging up to thousands of individuals, and often flying in large V-shaped formations. These smaller geese have calls that tend to be relatively higher pitched yelps and cackles. Wintering populations of Canada goose often occur as large, dense aggregations in the vicinity of good feeding habitat.

During the era of unregulated market and sport hunting of the nineteenth and early twentieth centuries, the populations of Canada geese were greatly reduced from their historical abundance. This decline was exacerbated by large losses of breeding habitat in the more southern parts of their range, largely due to the conversion of North America's prairies to agriculture, which was accompanied by the draining of many small, marsh-fringed ponds known as potholes. However, the federal governments of the United States and Canada, and the states and provinces, have since instituted effective conservation measures for the Canada goose and most other species of waterfowl. The most important of these actions is the regulation of hunting effort by restricting the numbers of birds that can be killed, and by limiting the hunting season to a period during the autumn and thereby eliminating the spring hunt, which killed animals before they had an opportunity to breed that year. Also very important has been the designating of a large network of protected areas, mostly to provide essential habitat and refuges from hunting for migrating and wintering waterfowl. In the case of the Canada goose, these measures have proven to be effective, and populations have recovered substantially from lows in the second decade of the twentieth century. At the end of the breeding season and during the autumn migration, North America now supports about three million Canada geese.

At least one million of these birds are subsequently killed by hunters, or by the insidious toxicity of ingested lead shot, or they may suffer natural mortality. Young, relatively inexperienced birds-of-the-year are most commonly killed by hunters, with the more wary adult birds tending to survive this type of predation. This is an important aspect of the hunt, because it results in the reproductive capacity of the population being left relatively intact. It appears that present-day populations of Canada geese are capable of withstanding the intense, annual mortality they are exposed to through hunting and other factors. However, it is important that this situation be continuously monitored, so that any emergent problems are quickly identified, and actions taken to prevent future population declines of this important species of wildlife.

The snow goose is another abundant species of goose in North America, tending to breed to the north of the major range of the Canada goose. This mostly white goose is often divided into two races, the relatively abundant and widespread lesser snow goose (C. c. caerulescens) and the greater snow goose (C. c. atlantica) of the high Arctic. The lesser snow goose has two color variants, the familiar white-bodied form with black wing-tips, and the so-called "blue" variant. The blue phase is genetically dominant over the white, and it occurs most frequently in the populations of snow geese breeding in the eastern low Arctic of Canada.

Like the Canada goose, the snow goose has been exploited heavily, and its populations were once imperilled by overhunting and habitat loss, especially of wintering habitat. However, strong conservation measures have allowed a substantial increase in the abundance of this species, which, although still hunted, may be approximately as abundant as prior to its intensive exploitation. In fact, since the 1980s, the rapidly increasing breeding populations of snow geese have caused significant degradations of parts of their habitat in the vicinity of Hudson Bay, through overgrazing of important forage species.

Brant and black brant are less common species of goose, occurring in eastern and western North America, respectively. These species are ecologically different from the other North America geese, because of their affinity for estuarine habitats, where they prefer to forage vascular plants known as eelgrass (Zostera marina). The brant is less abundant than it used to be, because of overhunting, and degradations of its wintering habitat, caused in part by occasional declines of its preferred forage of eelgrass. The causes of the eelgrass declines have not been determined, but they may be natural in origin, or somehow caused by human influences, possibly associated with eutrophication. In some years, these geese have also suffered reproductive failures due to unfavorable weather in their northern breeding grounds. This circumstance may also have contributed to the decline of brant.

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Science EncyclopediaScience & Philosophy: Gastrula to Glow dischargeGeese - Geese Of North America, Economic Importance Of Geese, Factors Affecting The Abundance Of Geese, Status