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

Concluding Remarks

In Part One we sought to determine if fox predation could be causing imbalanced sex ratios in mallards of the magnitude typically observed. To this end we developed a model of the phenomenon and applied previously unavailable data to it. The model was robust with respect to variations in the input parameters and stable with respect to time. A direct mathematical technique similar to that of Wight et al. (1965) provided additional verification of our results.

The spring sex ratio in the simulated 11th year was about 126 males per 100 females, consistent with published and unpublished field data. Fall sex ratios and rates of summer mortality were compared to published data; results were generally in agreement, although small samples precluded a definitive conclusion. An examination of other major mortality factors did not indicate any that were severe enough and sufficiently hen-selective to cause an appreciable sex disparity in the mallard population.

We conclude that fox predation (including accumulation of scavenged birds) alone is adequate to distort the sex ratio of a mallard population to the extent observed in the field.

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