Northern Prairie Wildlife Research Center
Impact of Red Fox Predation on the Sex Ratio of Prairie Mallards
Part Three: Historical and Geographical Perspectives
Searching questions have been raised about the history and causes of disparate
sex ratios in ducks (Dzubin 1970; Aldrich 1973) because, as pointed out by Bellrose
et al. (1961:427), "It seems reasonable to question the value of those drakes
in excess of the number needed to provide mates for the hens in waterfowl populations.
In the event such drakes do not play an essential role in species survival,
an effort should be made to provide for their utilization." The implication
of our findings is that "extra" drakes are indeed present in prairie mallard
populations, largely due to differential adult mortality rates from red fox
predation and hunting. Our findings will draw greater attention to these "extra"
drakes and, therefore, it is imperative to understand how present sex ratios
came to be. Before the supernumerary drakes are harvested we must determine
if disparate sex ratios of the magnitude observed today are a result of natural
evolutionary mechanisms that enhance the survival of the species or if they
are largely an artifact of modern man's activities.
Our North Dakota reference area is part of the Prairie Pothole Region of
central North America, which includes the aspen parkland transition area to
the north. Although the Prairie Pothole Region is a relatively small part
(12%) of the North American mallard breeding range (Fig.9),
it is the nesting ground for about half of the continental mallards (Pospahala
et al. 1974). Because of the large number of mallards nesting in the Prairie
Pothole Region, factors that significantly affect mallards there are of consequence
to the continental population.
The Prairie Pothole Region was settled by Europeans during the past 100
years; since settlement began there have been considerable changes in mallard
habitats, human interactions with mallards, and predator compositions and
densities. Our purpose in Part Three is to examine the changes in our North
Dakota reference area since pristine times that relate to mallard sex ratios
and to place them in perspective relative to the entire Prairie Pothole Region.
Emphasis is on factors affecting densities and distributions of mallards and
of canids. Finally, we conclude by employing the predictive model of Part
Two to reconstruct probable mallard sex ratios during pristine times in that
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