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Distribution and Abundance of Predators that Affect
Duck Production: Prairie Pothole Region

The Prairie Pothole Region


Before settlement, the prairie pothole region was largely treeless prairie that merged into transition forest along its eastern, northern, and western edge (Bird 1961; Kiel et al. 1972). This vast expanse was occasionally interrupted by river valleys and groups of forested hills (e.g., Moose Mountains [Saskatchewan], Riding Mountains [Manitoba], Turtle Mountains [Manitoba and North Dakota]). The prairie habitat reflected the region's low to moderate annual precipitation, periodic droughts, uncontrolled prairie fires, and immense herds of bisons (Bison bison; Roe 1939; Bird 1961; Lynch 1964; Kiel et al. 1972; Higgins 1986). A zone of trees (primarily quaking aspen [Populus tremuloides]) and brush (primarily willows [Salix spp.]) around edges of wetlands separated the prairie from the transition forest. This zone, known as the aspen parkland, is included in our definition of the prairie pothole region (Fig. 1). Encroachment of trees and brush into the prairie was held in check by prairie fires, periods of drought, and grazing by ungulates (Archibold and Wilson 1980; Houston and Bechard 1983; Higgins 1986).

Settlement of the prairie pothole region by Europeans began in earnest about 1870 (Strange 1954; Bird 1961; Robinson 1966; Kiel et al. 1972). The building of railroads during the 1880's opened the region to a great influx of settlers who quickly changed the region's economy from hunting and fur trading to farming. Land was surveyed into sections (2.59 km2) and distributed by the Canadian and United States governments to encourage settlement. Railroad companies and others were granted large blocks of land, much of which they subsequently sold in section and quarter section (0.65 km2) units. Homesteaders were granted smaller tracts, generally quarter sections (Strange 1954; Robinson 1966; Watkins and Watson 1975). Roads were established on section boundaries (Kiel et al. 1972). Because of this pattern of land ownership and rural development, sections and quarter sections are still clearly discernible in most areas (i.e., marked by roads, trails, fences, and field edges).

Settlement resulted in human exploitation of the region's animal populations and conversion of native grasslands to farmland and pastures (Kiel et al. 1972). Bison herds and uncontrolled fires were largely eliminated by the late 1800's (Kiel et al.1972; Higgins 1986). Trees and brush invaded portions of the prairie and widened the aspen parkland (Kiel et al. 1972; Edwards 1976; Archibold and Wilson 1980; Houston and Bechard 1983; Higgins 1986). Agricultural development resulted in plowing of most grassland, draining and other modifications of tens of thousands of wetlands, widespread planting of trees for windbreaks, and destruction of woody borders around wetlands (Bird 1961; Robinson 1966; Bellrose 1976; Merriam 1978; Turner et al. 1987). Presently, nearly all land is used to grow crops or graze livestock; in many areas, over 80% of upland is cultivated annually (Higgins 1977: Sugden and Beyersbergen 1984. Anthropogenic habitat changes continue to occur throughout the region (Fig. 2).


jpg -- Photographs of Habitat Modifications

Figure 2. Habitat modifications in and in the vicinity of study areas in the prairie pothole region during 1983-88: (a) drainage of wetlands, (b) plowing of native prairie pasture, (c) removal of aspen trees around wetland, and (d) intensive grazing by livestock and removal of rocks in preparation for plowing.

Predator populations in the prairie pothole region have been directly affected by humans (e.g., human-inflicted mortality) and by extensive habitat changes from agricultural development. Some predator species that were common and widely distributed before settlement vanished from all or most of the region (e.g., swift fox [Vulpes velox], gray wolf [Canis lupus]), whereas populations of some other species that were scarce and narrowly distributed expanded greatly (e.g., raccoon [Procyon lotor], American crow [Corvus brachyrhynchos]; Soper 1946; Adams 1961; Bird 1961; Johnson 1969; Banfield 1974; Cowan 1974; Houston 1977; Jones et al. 1983; Carbyn 1984).


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