Impact of Red Fox Predation on the Sex Ratio of Prairie Mallards
Concluding Remarks
It is apparent from our discussion that the sex ratio of mallards throughout the Prairie Pothole Region has become increasingly a function of human-related mortality factors. Some factors such as fox predation are hen selective, others such as hunting are drake selective, and all have undergone considerable changes in intensity. Thus, since settlement, the sex ratio of mallards in the Prairie Pothole Region can hardly be considered the product of some adaptive strategy. Rather, it seems to be largely the result of human activity, and there is little reason to believe that it is the same as during pristine times or that it represents an optimal level for the species. The combination of interacting factors has likely increased sex disparity of mallards in our North Dakota reference area from about 110:100 or less to 120:100. Elsewhere in the mallard's breeding range, predation and hunting may operate with different intensity and sex specificity, resulting in sex ratios different from those of prairie mallards.
Within the entire Prairie Pothole Region, conditions for a strongly disparate sex ratio are probably nearly maximized in North Dakota, because of lower mallard populations, intense agriculture, and a 30-year period of relatively high red fox populations. During the past 10 to 20 years, however, conditions in the prairie provinces of Canada, especially in Saskatchewan and very recently in Alberta, have changed toward those in North Dakota, thus narrowing the differences in the nature of mortality factors affecting mallards. We suggest that the impact of red foxes on the sex ratios of mallards is now a phenomenon of the entire Prairie Pothole Region and that nonhunting mortality of hen mallards and thus sex disparity have increased.
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