Interpreting Evidence of Depredation of Duck Nests
in the Prairie Pothole Region
by
Alan B. Sargeant
Marsha A. Sovada
Raymond J. Greenwood
United States Department of the Interior
United States Geological Survey, Biological Resources Division
Ducks Unlimited, Inc.
Introduction
Factors affecting duck production in the Prairie Pothole Region (Fig. 1) are of special interest to researchers and managers of waterfowl, because the region is a major breeding ground for North American ducks (Smith et al. 1964, Bellrose 1980). Biologists, concerned about the welfare of prairie ducks, began investigating nest success of these birds in the 1930's (Kalmbach 1937a, 1937b, 1938, 1939). Through these initial and subsequent studies, fates of >25,000 duck nests have been determined (Sargeant and Raveling 1992).
High predation rates of female ducks and nests (Klett et al. 1988, Higgins et al. 1992, Sargeant and Raveling 1992, Greenwood et al. 1995) stimulated interest in identifying the predator species. As a result, literature of duck nest success often includes general (Keith 1961, Higgins 1977) or specific (Stoudt 1971, Duebbert and Lokemoen 1976, Higgins et al. 1992) assignments of depredated nests to predator species. Waterfowl managers need to identify predator species responsible for nest depredations to develop strategies to reduce predation. However, nearly all assignments of destroyed nests to predator species are based on subjective interpretations of evidence found at nests.
Investigators have recognized the difficulty of interpreting evidence of depredation and "...the necessity of correctly reading signs (of predators) at destroyed nests" (Kalmbach 1937a:5). Although several studies provide interpretive evidence of depredation, available information is meager, often ambiguous, and sometimes contradictory (Baker 1978, Appendix A). Because literature on identification of predators of duck nests may be erroneous and lack specific criteria for identifying predators, it cannot be evaluated for accuracy.
We believe that identification of predators of duck nests, based on evidence found at nests, will be valuable to researchers and managers. However, for such information to be useful, it must be collected and interpreted more objectively than in the past. The primary purpose of this report is to help investigators more accurately and objectively collect and interpret evidence of depredation at duck nests in the Prairie Pothole Region. Our report is divided into 3 parts:
- A summary of biological factors that affect evidence of depredation typically found at duck nests.
- A summary of literature and our experiences concerning evidence of depredation by predator species.
- A discussion of interpreting evidence of depredation at duck nests, with examples for certain predators.
This report pertains primarily to duck nests in uplands or dry portions of wetlands. We use subjective terms to describe frequency of most predator behaviors because of a general lack of definitive data. When possible (based on data and personal observations), we use the following italicized terms to convey general categories of frequency: seldom or occasionally = ≤10%, often = 11-50%, usually = 51-90%, and customarily = ≥91%. We use "at nest" or "nest site" to refer to the 3-m radius area around nests, and "near nest" to refer to the radius interval 3-20 m from nests. We include a glossary for clarification of certain terms. We urge readers to become familiar with definitions in the glossary before proceeding. A format for recording evidence of depredation is provided in Appendix D.
This resource is based on the following source (Northern Prairie Publication 1030):
Sargeant, A. B., M. A. Sovada, and R. J. Greenwood. 1998. Interpreting
evidence of depredation of duck nests in the prairie pothole region.
U.S. Geological Survey, Northern Prairie Wildlife Research Center,
Jamestown, ND and Ducks Unlimited, Inc., Memphis, TN. 72pp.
This resource should be cited as:
Sargeant, A. B., M. A. Sovada, and R. J. Greenwood. 1998. Interpreting
evidence of depredation of duck nests in the prairie pothole region.
U.S. Geological Survey, Northern Prairie Wildlife Research Center,
Jamestown, ND and Ducks Unlimited, Inc., Memphis, TN. Jamestown,
ND: Northern Prairie Wildlife Research Center Online.
http://www.npwrc.usgs.gov/resource/birds/depred/index.htm
(Version 02JUL99).
Table of Contents
- Abstract
- Reference Area and Predator Species
- Part I: Factors Affecting Evidence of Depredation
- Characteristics of Eggs
- Characteristics of Nests and Nest Sites
- Behavior of Ducks
- Anatomy and Size of Predators
- Effects of Other Animals
- Part II: Evidence of Depredation by Predator Species
- Methods Used to Obtain Original Data
- Coyotes and Red Foxes
- Raccoons and Stiped Skunks
- American Badgers
- Minks and Weasels
- Franklin's Ground Squirrels
- Black-billed Magpies, American Crows, and Gulls
- Depredation Patterns of Predator Species
- Coyotes
- Red Foxes
- Raccoons
- Striped Skunks
- American Badgers
- Minks
- Weasels
- Franklin's Ground Squirrels
- Black-billed Magpie
- American Crow
- Gulls
- Methods Used to Obtain Original Data
- Part III: Interpreting Evidence of Depredation
- Limitations of Data
- Estimating Proportion of Nests Destroyed by a Predator Species
- Defining the Question
- Delineating the Data
- Establishing a Hierarchy of Criteria
- Examples of Interpreting Data Recorded on Nest Depredation Records
- Acknowledgments
- Literature Cited
- Glossary
- Appendices
- Appendix A: Literature of Patterns of Depredation of Duck Nests by Predators in the Prairie Pothole Region
- Appendix B: Tables
- Table 1: Distance between tips of both upper and lower canine teeth of principal mammalian carnivores of duck nests in the Prairie Pothole Region.
- Table 2: Comparison among principal predators of duck nests in the Prair Pothole Region.
- Table 3: Frequency of various types of damage among eggshells.
- Table 4: Frequency of eggshells of duck nests depredated by predatorys of duck nests.
- Table 5: Frequency of depredated duck nests by classes of percentage of nest material displacement.
- Table 6: Distribution of eggshells by distance intervals at duck nests.
- Table 7: Stepwise application of specified criteria to estimate the proportion of destroyed incubated duck nests of ≥6 eggs in uplands caused by red foxes.
- Table 8: Stepwise application of specified criteria to estimate the proportion of destroyed incubated duck nests of ≥6 eggs in uplands caused by striped skunks.
- Table 9: Stepwise application of specified criteria to estimate the proportion of destroyed incubated duck nests of ≥6 eggs in uplands caused by raccoons.
- Appendix C: Photographs of Eggshells From Eggs Depredated by Individual Predator Species
- Appendix D: Format for Quantifying Evidence of Depredation of Duck Nests
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