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Impact of Red Fox Predation on the Sex Ratio of Prairie Mallards

Part Four: Implications of a Distorted Sex Ratio

The implications of distorted sex ratios in ducks fall into two broad categories, biological (the effect on the species) and management (the importance to man, particularly the hunter). Most interest in the subject has been generated because of the management implications as they relate to the possibility of harvesting the "excess" drakes. We emphasize that the management implications cannot be adequately assessed without knowledge of the biological importance of the supernumerary drakes.

Several workers, who probed the role of "excess" drakes in duck populations, raised many critical questions to which answers are needed, especially if consideration is given to reducing drake populations to parity or lower. Bellrose et al. (1961:428) suggested, "Insight into the value of extra drakes could be obtained through an experimental procedure designed to reduce the number of drakes in a subpopulation of a species having a large drake segment." Such a study has yet to be conducted although ongoing research in north-central Iowa is directed toward answering some of the questions (R. A. Bishop, personal communication). Dzubin (1970) reviewed the subject of "excess" drakes and listed seven important questions, one of which pertained to the nature of sex ratios during pristine times, a subject addressed in Part Three. Largely unanswered are his other questions, most of which deal with the possible role of supernumerary drakes in the mallard breeding biology.

Part Four focuses on the implications resulting from a population containing more males than females. We summarize the possible roles of supernumerary drakes in breeding biology and discuss probable differences in the cause and magnitude of disproportionate sex ratios among dabbling and diving ducks. We also discuss management implications of the presence of "extra" drakes, specifically in regard to interpretation of breeding pair counts and in regard to harvest regulations, and touch upon the concept of predator management as it pertains to control of red fox populations.

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