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A. Prairie-parkland Region

The prairie-parkland region encompasses about 777,000 km² (Fig. 12-1) of mixed prairie and aspen parkland habitats that contain millions of small wetlands used for reproduction by many waterfowl species. This temperate region is also excellent for agricultural production, especially of cereal grains, and for grazing livestock. During the past 110 years this region has been transformed from grassland and parkland wilderness to intensively used farmland (Bird 1961, Kiel et al. 1972). The drainage of prairie wetlands, up to 90% or more in some areas, has long been recognized as a serious threat to maintenance of abundant waterfowl in the region (Pospahala et al. 1974, McCorkle and Halver 1982). Recently, it has become apparent that human impacts on uplands and on certain animal populations of the region have led to high mortality rates of waterfowl females, eggs, and young during the breeding season (Johnson and Sargeant 1977, Cowardin et al. 1983a, Sugden and Beyersbergen 1984).

Waterfowl in the prairie-parkland region appear to be at greater risk of mortality during the breeding season from a broader variety of agents than are waterfowl in other major breeding areas of North America (Table 12-1, Table 12-2, Table 12-3, Table 12-4, and Table 12-5). Yet waterfowl in the prairie-parkland region also have greater capacity to withstand severe mortality than do waterfowl in most other regions. The temperate climate and abundant fertile wetlands provide for a strong reproductive effort with potential for considerable renesting (e.g., Sowls 1955, Calverley and Boag 1977, Bellrose 1980). The resulting high reproductive potential and wide distribution of prairie-parkland waterfowl tend to buffer populations from effects of high mortality during initial breeding efforts or in local areas. The only major mortality factors that currently appear to be absent or inconsequential in this region are tidal floods and subsistence hunting. Factors that are relatively specific to this region or that seem to affect greater proportions of populations in this region than elsewhere are hail, collisions, and predation. The effects of contaminants and disease are unknown, but the widespread use of agricultural chemicals has potential to be an important mortality factor (Sheehan et al. 1987).

Of the numerous nonhunting mortality factors affecting waterfowl in the prairie-parkland region during the breeding season, predation appears to have the greatest influence. The negative effect of predators on waterfowl production in the region has likely increased as a result of agricultural development. Human-inflicted mortality on predators, interspecific predator interactions, and habitat changes (Bird 1961, Kiel et al. 1972, Johnson and Sargeant 1977, Cowardin et al. 1983a) have resulted in major changes in the species composition and abundance of predators. For example, populations of coyotes, American Crows, raccoons, and red foxes, all of which prey extensively on nesting waterfowl or their eggs, have expanded greatly in much of the region (Kalmbach 1937; Stoudt 1971; Johnson and Sargeant 1977; A. B. Sargeant, unpublished data). Coincident with expansion of numbers or ranges of these predators were reductions or eliminations of populations of grizzly bears, gray wolves, and kit foxes from the region (Jones et al. 1983). These latter species are not known to be major predators of nesting ducks or their eggs and young.

Intensive farming has concentrated waterfowl nests and reduced availability of alternative prey for predators, thereby contributing to high predation rates in the prairie-parkland region. In large parts of the region more than 80% of the upland is cultivated annually (Higgins 1977, Sugden and Beyersbergen 1984). Few waterfowl except Northern Pintails nest frequently in cropland because of lack of suitable cover (Milonski 1958, Higgins 1977, Klett et al. 1988). Hence, most waterfowl nests in the prairie-parkland region are in the remaining untilled habitats where predators concentrate their foraging activities (Cowardin et al. 1983a). Although definitive data on relationships between changes in prey abundance and predation rates on waterfowl in this region are lacking, it is likely that decreased abundance of alternative prey has increased predation on waterfowl here as it has in other areas (e.g., Larson 1960, McInvaille and Keith 1974, Pehrsson 1986).

B. Artic Tundra Region

The arctic tundra in North America, defined as that region north of the tree line and characterized by lichens, mosses, and graminoid vegetation, extends more than 5,000 km from coastal Alaska to Labrador (Fig. 12-1). The most important breeding habitats for geese and most other waterfowl in the region are sedge and grass plains concentrated near coasts, especially at river deltas. Many river deltas provide an abundance of small islands and ponds that are especially attractive to nesting waterfowl. Thus, waterfowl populations in the arctic, many of which nest colonially, exhibit a more discontinuous distribution than do waterfowl in the prairie-parkland region.

The cold climate and attendant short ice-free season in the arctic tundra region restrict nesting by most waterfowl species, especially swans and geese, to a single, highly synchronized attempt. Thus, waterfowl populations in the region are less buffered from perturbations negatively affecting their abundance and do not have as great a potential for rapid population recovery as do waterfowl in more temperate regions. Sporadic, severe oscillations in reproductive success of arctic-nesting waterfowl are common natural occurrences that, in the main, have only temporary effects on populations. These oscillations, however, reflect the relative fragility of waterfowl breeding populations in the region.

Mortality agents that have had greatest direct influence on population levels and annual recruitment of waterfowl in the arctic tundra region appear to be weather, predation, and subsistence hunting. Contaminants and disease have not been identified as major sources of mortality, although the full effects of these two mortality agents are not understood.

It is difficult to generalize about the relative importance of each mortality agent affecting breeding waterfowl in the arctic tundra region, because impacts vary greatly among species, areas, and years. Weather is an unpredictable natural event that primarily affects survival of eggs and young (Tables 12-2, 12-4). The fact that a single storm can severely depress survival or recruitment in local populations makes weather an important mortality agent, especially for waterfowl stocks concentrated in relatively small areas (King 1965 in Eisenhauer and Kirkpatrick 1977, Barry 1968).

Predation is a major mortality factor for waterfowl breeding populations throughout the arctic tundra region, primarily through destruction of eggs and young. However, unlike the situation in the prairie-parkland region, relatively few predator species have a significant effect on most waterfowl populations. The predators of greatest consequence are jaegers, large gulls, and arctic fox. The balance between the distribution and abundance of arctic fox and the locations and abundance of breeding waterfowl can be easily altered by both natural events and, especially, human activities. The consequences of such changes to waterfowl populations can be severe, including decimation of local populations, especially of geese and eiders (e.g., release of arctic foxes on islands [Murie 1959] or sustaining high fox populations by providing carrion from harvests of sea mammals [Larson 1960, Bousfield and Syroechkovskiy 1985] or garbage associated with petroleum development activities [Eberhardt et al. 1983]).

Although the natural habitats of the arctic tundra region are largely intact, waterfowl breeding populations in certain parts of this region have been adversely affected by human activities, especially modern subsistence hunting (Raveling 1984, Bousfield and Syroechkovskiy 1985, King and Derksen 1986). Unlike predation, subsistence hunting tends to impact certain populations heavily while having relatively little effect on others. The waterfowl species or populations most affected by subsistence hunting have been those with relatively small, localized breeding ranges in the vicinity of villages. The recent plights of the Emperor Goose, White-fronted Goose, Cackling Canada Goose, and Brant on the Yukon-Kuskokwim Delta are examples of populations affected by subsistence hunting (Raveling 1984, King and Derksen 1986).