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Long-term Declines in Nest Success of Prairie Ducks

Management Implications

We found evidence that nest success declined between the 1930s and 1992, albeit more slowly than previous estimates, for all 5 species examined. But census data indicate gadwalls and northern shovelers have not shown concurrent population declines, and have actually increased in some areas (Dickson 1989). Together, these observations are inconsistent with the idea that nest success is a principal cause of variation in population size. Management aimed at increasing nest success implicitly assumes that it will lead to increases in fall flight and recruitment to the breeding population. Others have acknowledged that nest success may not be the only, or most important, factor limiting population growth (Cowardin et al. 1985, Clark and Nudds 1991). Accordingly, more attention is being directed to brood survival (Talent et al. 1983, Orthmeyer and Ball 1990, Rotella and Ratti 1992) and survival throughout the annual cycle (Hill 1984, Johnson et al. 1988b, Hestbeck et al. 1989).

The widespread nature of declining nest success implies that a large-scale solution would be required to reverse the trend. In general, it may be more cost-effective to direct efforts toward encouraging extensive management (recovery of marginal farmland, alternative farming practices), rather than intensive, site-specific management (e.g., direct predator control programs). However, in severely altered landscapes, intensive management (however expensive) might be the only way to augment nest success, but this question still needs to be addressed (Clark and Nudds 1991, Nudds and Clark 1992). Whatever decisions are made regarding the management of nest predators in particular circumstances, we advocate its implementation in ways that the effects can be properly evaluated by the most rigorous means possible (Macnab 1983, Clark and Nudds 1991, Clark and Diamond 1993).

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