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Major change is occurring in the distribution and abundance of canids in the PPR of North Dakota and South Dakota; coyote populations are expanding. This change has important ramifications to waterfowl research and management. If the trend continues, duck nest success may be higher than it has been since the 1940s when foxes were the principal canid in much of this area (Johnson and Sargeant 1977, Sargeant et al. 1993, Sovada 1993). Our results are from publicly owned land managed for duck production, but the differential effects of coyotes and red foxes probably apply to duck production in all lands in the sampled localities. If effects of the canid community on duck nest success are as substantial in all lands as we found, it is difficult to envision other factors that could have greater positive influence on duck nest success in the PPR, except possibly major changes in agricultural programs, climate, or other predator populations.

In most areas, substantial coyote mortality is caused by humans (Harrison 1986, Voigt and Berg 1987, Gese et al. 1989). In the PPR, this source of mortality was believed to be the principal cause of low coyote populations (Johnson and Sargeant 1977, Sargeant et al. 1993). Thus, distribution and abundance of coyotes, and hence foxes, in much of the PPR probably can be manipulated by regulating coyote harvest. Managing coyote harvests may be a cost-effective means for increasing duck nest success on public and private lands. Disease also may regulate numbers of coyotes and foxes, but has not been reported as a major factor in long-term overall abundance of either species in the PPR.

Management to maintain or increase coyote populations is not without consequence; coyotes prey on big game species and livestock (Till and Knowlton 1983, Harrison and Harrison 1984, Andelt 1987). Coyotes also may have deleterious effects on ground-nesting bird species such as Canada geese, which may be able to defend themselves and their nests from foxes (Hanson and Eberhardt 1971, Campbell 1990). However, on the basis of findings of Sargeant et al. (1987) and Harrison et al. (1989), we believe a density of about 1 family (2-4 ad)/25 km² would be optimal to depress fox populations and benefit nesting ducks.