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

Population Trends

Our review of the literature revealed that throughout the prairie pothole region population levels of nearly all predator species have varied greatly since settlement began. Populations of species that were unable to adapt to the rapidly changing environment or were wantonly over-harvested for profit or because they conflicted with human interests diminished rapidly in abundance, distribution, or both, some to extirpation. Populations of other species increased by taking advantage of newly created habitats, absences of certain competitors, or both. The magnitude of changes that occurred during the late 1800's was enormous.

Changes during the early 1900's to the mid 1930's in levels of predator populations were more gradual, but exploitation of nearly all predator species affecting ducks was extremely heavy (Johnson 1964). Numerous authors ret er to heavy exploitation and low numbers of most predator species during this period (Dearborn 1920; Osborn and Anthony 1922; Bird 1930; Farley 1932; Kiel et al. 1972; Sargeant 1982). A notable exception was that abundance of American crows expanded greatly in spite of severe persecution (Johnson 1964). Ducks nesting in the prairie pothole region during this period were probably at lower risk from predation than during any other period since settlement began.

The severe drought and the economic depression of the mid-1930's caused abandonment of large numbers of farmsteads (Robinson 1966). Declining fur prices reduced human harvests of many predators. In the early 1940's, World War II further reduced direct human influence on the abundance of predators, even though fur prices surged for a few years, through military conscriptions and restrictions on ammunition and motorized transportation (Bihrle 1990). Modern game management began early in this period and collection of quantitative data about the abundance of predators commenced (Adams 1961). Populations of at least three major predator species affecting duck production (red fox, raccoon, and American Crow) expanded rapidly in various parts of the region (Adams 1961; Kiel et al. 1972; Sargeant 1982; Sanderson 1987).

Post World War II brought about mechanized agricultural activities and a mobile public with strong interests in outdoor activities but low regard for most predators (Kirkpatrick and Elder 1951; Sargeant 1982). Pelt prices of many predator species, especially those with long fur, were exceptionally low from the mid-1940's until the late 1960's, especially in the United States. Red fox and raccoon populations continued to expand in the United States portion of the region and bounties were widely used in attempts to reduce numbers of red foxes and other predators (Hubert 1982). However, bounties generally failed to reduce populations to low levels. Populations of most avian predators, especially raptors, did not flourish and some declined because of increased use of agricultural chemicals (e.g., DDT, which caused eggshell thinning among some raptors [Anderson and Hickey 1972; Evans 1982]), continued deliberate killing by humans, and continued habitat losses.

A particularly important activity during the 1940-60's was the effective widespread use of toxicants, especially compound 1080 (sodium monofluoroacetate) for the control of coyotes. Compound 1080 was widely used beginning in the late 1940's in the United States and later in Canada (U.S. Fish and Wildlife Service 1978; Andelt 1987). Bounty records showed that red foxes did not become common in western North Dakota until the mid-1950's, after coyote populations had been reduced (Adams 1961). Stoudt (1971) reported that red foxes became numerous and raccoons first appeared in the Redvers area of southeastern Saskatchewan shortly after coyote numbers were greatly reduced by a control program in the early 1950's that involved use of compound 1080. By the late 1960's, red foxes were abundant throughout nearly all of the southeastern portion of the prairie pothole region. Attitudes toward predators then began to change as a result of growing concern for predators, especially raptors, and the high costs and general ineffectiveness of bounties. By the late 1960's, bounties on predators had been largely discontinued (Hubert 1982; Slough et al. 1987).

Since the late 1960's, growing concern for the welfare of wildlife, including predators (Cain et al. 1972), resulted in restrictions in predator control programs (U.S. Fish and Wildlife Service 1978) and increased attention to management of furbearers and protection of avian predator species. Use of toxicants was greatly reduced throughout the prairie pothole region early in this period (U.S. Fish and Wildlife Service 1978). Also, the use of aircraft, snowmobiles, and other all-terrain vehicles for pursuing coyotes and red foxes was greatly restricted in nearly all areas. For example, in 1968 the red fox in North Dakota was unprotected and could be legally killed anytime by almost any means including aerial hunting, destruction of pups in dens, and toxicants. By 1974, the red fox had been reclassified as a furbearer with a 197-day harvest season. Destruction of pups in dens, aerial hunts, chases with snowmobiles, and toxicants were banned except under special circumstances. During this period, raptors were afforded considerable protection in Canada and the United States (Bond 1974; Heintzelman 1979). In the United States, the American crow was protected as a migratory bird and could be killed only during established seasons. When our study commenced, only a few predator species were still unprotected in most areas (e.g., striped skunk, Franklin's ground squirrel, and, only in Canada, American crow and black-billed magpie).

Whereas the complete protection of raptors resulted from public concern for such birds, much of the concern for carnivores after the 1960's resulted from resurgence of high fur prices that rivaled those of the early 1900's. However, because of government regulations, fur harvests reduced few mammalian predator populations throughout large areas to low levels during this period. In southeastern portions of the prairie pothole region, the coyote benefitted from harvest restrictions and expanded its populations (A. B. Sargeant, personal observations). The reverse may have occurred in some heavily farmed areas of Canada where coyotes had been present but were heavily harvested.

Nobody can accurately predict the magnitude of changes in the future abundance and distribution of predator species. Gradual changes will probably occur as habitats continue to be altered. Changes in direct and indirect human-inflicted mortality rates of species, especially severe curtailments of human-inflicted mortality, may result in expansion of the population of some species to the detriment of others. Questions to be answered include: Will raptor populations increase substantially and result in interspecific exclusions, will American crows become numerous again in the southern portion of the region, and will coyote populations expand further and cause major declines in abundance of red foxes and possibly raccoons?

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