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I. Introduction

Waterfowl populations fluctuate in response to continuously changing conditions that affect the balance between natality and mortality. A reproductive potential far in excess of that needed for replacement provides the pool of individuals upon which natural selection operates. Waterfowl management in North America is aimed primarily at maintaining populations large enough to sustain desired levels of harvest by people. Much of this management effort focuses on encouraging high natality and substituting hunting for nonhunting mortality. An unresolved issue is the significance of compensatory adjustments within populations (Anderson and Burnham 1976, Nichols et al. 1984). For example, to what extent is increased mortality from hunting compensated for by decreased nonhunting mortality? We raise this issue because of its importance in assessing the significance of various mortality agents but, like others, we cannot resolve it.

In this chapter we address mortality of waterfowl adults, eggs, and young during the breeding season (period from arrival of adults on nesting areas to fledging of young). Annual population sizes reach both their lowest and highest levels during the breeding season. Our emphasis is on North America, especially the prairie-parkland and arctic tundra regions (Fig. 12-1), and on species nesting in natural sites in nonurban environments. We emphasize these aspects because: (1) studies of mortality of breeding waterfowl and their nests and prefledged young in these regions are more common than elsewhere, (2) these regions are primary breeding areas for several heavily hunted waterfowl species, and (3) we are personally familiar with waterfowl in these regions. In selecting this emphasis we neglected some quantitative data on introduced species, waterfowl nesting in man-made structures, and waterfowl in urban situations where they are affected by human harassment or protection.

See Figure 12-1.

Sargeant, Alan B., and Dennis G. Raveling.  1992.  Mortality during the breeding
     season.  Ecology and Management of Breeding Waterfowl.  University of
     Minnesota Press, Minneapolis, MN.  Chapter 12:396-422

Sargeant, Alan B., and Dennis G. Raveling.  1992.  Mortality during the breeding
     season.  Ecology and Management of Breeding Waterfowl.  University of
     Minnesota Press, Minneapolis, MN.  Northern Prairie Wildlife Research
     Center Online.  
     http://www.npwrc.usgs.gov/resource/birds/ecomanag/chap12/chap12.htm
     (Version 02FEB99).

Table of Contents

• Methods for Assessing Mortality
  • Adults
  • Eggs
  • Prefledged Young
• Mortality Rates
  • Adults
  • Eggs
  • Prefledged Young
• Mortality Agents
  • Collisions
  • Weather
  • Predation
  • Contaminants
  • Disease
  • Subsistence Hunting
  • Miscellaneous
• Principal Mortality Agents in Two Major Breeding Areas
  • Prairie-parkland Region
  • Arctic Tundra Region
• The Significance of Breeding-Season Mortality
  • Ducks in the Prairie-parkland Region
  • Geese in the Arctic Tundra Region
• Conslusion
• Acknowledgments
• References

Tables

• Table 1 -- Some Breeding Season (April-September) Mortality Rates of Adult Female Ducks in North America and Principal Causes of Mortality.
• Table 2 -- Some Mortality rates of Swan and Goose Nests in North America and Principal Causes of Mortality.
• Table 3 -- Some Mortality Rates of Duck Nests in North America and Principal Causes of Mortality.
• Table 4 -- Some Mortality Rates of Prefledged Swans and Geese in North America and Principal Causes of Mortality.
• Table 5 -- Some Mortality Rates of Prefledged Ducks in North America and Principal Causes of Mortality.