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Johnson, Douglas H. and Alan B. Sargeant  1977.  Impact of red fox predation on 
     the sex ratio of prairie mallards.  U.S. Fish and Wildl. Serv. Wildl. Res. 
     Rep. 6.  56 pp.

Johnson, Douglas H. and Alan B. Sargeant  1977.  Impact of red fox predation on 
     the sex ratio of prairie mallards.  U.S. Fish and Wildl. Serv. Wildl. Res. 
     Rep. 6.  56 pp.  Northern Prairie Wildlife Research Center Online.  
     http://www.npwrc.usgs.gov/resource/mammals/sexratio/sexratio.htm
     (Version 16JUL97).

Table of Contents

• Foreword
• Abstract
• Introduction

• Part One: A Model of Fox Impact on Mallard Sex Ratios
  • Basics of the Model
    • Reference area and time period
    • Components of the model and their relationships
  • The Data
    • Spring densities of red foxes
    • Spring densities of male mallards
    • Fox predation rates on mallards
    • Adult mallard survival rates
    • Hunting mortality rates of adult mallards
  • Operation of the Model
  • Results of the Simulations
    • Sensitivity analysis
    • Stability of the model
    • Limiting behavior of the sex ratio
  • Validation of the Simulation Results
    • The spring sex ratio
    • The fall sex ratio
    • Summer mortality rates
    • The sex specificity of other mortality factors
  • Concluding Remarks

• Part Two: Using the Model to Predict Sex Ratios
  • The Revised Model
    • A submodel for the fox population
    • A submodel for the mallard population
    • A submodel for predation rates
    • Rates of hunting and "other" mortality
  • The Predictions
    • Alterations in the fox population
    • Alterations in the mallard population
    • Alterations in the hunting rates
  • Implications of the Predictive Model

• Part Three: Historical and Geographical Perspectives
  • Settlement of the Prairie
  • Mallard Population Trends
  • Canid Composition and Population Trends
    • Gray wolf
    • Coyote
    • Red fox
  • Changes in Canid Predation Rate
    • Canid denisty changes
    • Canid predation effectiveness
  • Mallard Sex Ratios in Pristine Times
  • Concluding Remarks

• Part Four: Implications of a Distorted Sex Ratio
  • The Role of Supernumerary Drakes
  • Sex ratios in Other Species of Ducks
  • Management Implications
    • Effect of a sex disparity on surveys and censuses
    • Hunting considerations
    • Predator management

• Conclusion
• Acknowledgments
• References

Figures

• Figure 1: The Prairie Pothole Region of North Dakota
• Figure 2: Aerial View of the Drift Plain
• Figure 3: Aerial View of the Missouri Coteau
• Figure 4: Asymptotic Sex Ratio As a Function of the Ratio of Male to Female Survial Rates
• Figure 5: Expected Fox Population Change As a Function of the Size of the Population
• Figure 6: An Example of a 50-year Series of Fox Populations
• Figure 7: An Example of a 50-year Series of Male Mallard Populations
• Figure 8: The Expected Predation Rate as a Function of Prey Population
• Figure 9: The North American Breeding Range of the Mallard
• Figure 10: The Breaking of Virgin Prairie Sod in North Dakota
• Figure 11: Turn-of-the-century Photo Showing the Large Number of Waterfowl Killed by Hunters
• Figure 12: Spacing of Fox Families on a 269 km² area including the Arrowwood
• Figure 13: Movements of a Radio-Equipped Adult Female Red Fox on a Minnesota Study Area
• Figure 14: Plots Depicting the Simulated Effect of Reduced Predator Populations on Mallard Populations

• Table 1: Components of the Model
• Table 2: Relationships Among Components of the Model
• Table 3: Definitions of Rates Associated with the Equations in Table 2
• Table 4: Various Indices of Red Fox Densities and Estimated Spring Population of Red Fox Families
• Table 5: Estimates of Mallard Spring Breeding Population
• Table 6: Incidence of Mallards Found Above Ground at Red Fox Rearing Dens
• Table 7: Location of Mallards in Food Remains at Excavated Red Fox Dens
• Table 8: Proportion of Mallards Taken by Red Foxes That are Brought to Rearing Dens
• Table 9: Number of Dens Used by Red Fox Families to Rear Pups
• Table 10: Sex Ratios of Adult Mallards Found at Red Fox Dens
• Table 11: Estimated Red Fox Predation Rates on Mallards
• Table 12: Annual Survival and Recovery Rates for Adult Mallards
• Table 13: Means, Standard Deviations, and Correlations Among Adult Mallard Survival and Recovery Rates
• Table 14: Average Rates of Mortality From Various Causes
• Table 15: Average Sex Ratio and Rates of "Other" Mortality
• Table 16: Sex Ratios of Prenesting Mallards in the Northern Prairie Region
• Table 17: Sex Composition of Mallards Found on Roads in Eastern North Dakota 1969-74
• Table 18: Sex Composition of Adult Ducks Found at Mink Dens
• Table 19: Apportionment of Mallard Remians Found at Red Fox Dens
• Table 20: Parameters of Distributions Used to Generate Random Variates
• Table 21: Average Sex Ratios and Survival Rates Resulting From Various Settings of the Predictive Model