The effects of predator removal on mallard production and population change in northeastern North Dakota

Authors

  • Courtney L. Amundson,

    Corresponding author
    1. Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, 200 Hodson Hall, 1980 Folwell Ave., St. Paul, MN 55108, USA
    Current affiliation:
    1. USGS Alaska Science Center 4210 University Dr. Anchorage, AK 99508, USA.
    • Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, 200 Hodson Hall, 1980 Folwell Ave., St. Paul, MN 55108, USA
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  • Matthew R. Pieron,

    1. Louisiana State University Agricultural Center, School of Renewable Natural Resources, 341 Renewable Natural Resources Building, Baton Rouge, LA 70803, USA
    Current affiliation:
    1. Idaho Department of Fish and Game 3316 16th St., Lewiston, ID 83501, USA.
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  • Todd W. Arnold,

    1. Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, 200 Hodson Hall, 1980 Folwell Ave., St. Paul, MN 55108, USA
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  • Laura A. Beaudoin

    1. Department of Integrative Biology, University of Guelph, 50 Stone Rd. E., Guelph, ON N1G 2W2, Canada
    Current affiliation:
    1. Hatfield Consultants 100208 Centennial Dr., Fort McMurray, AB T9H 1Y5, Canada.
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  • Associate Editor: Michael Eichholz

Abstract

In 1994, Delta Waterfowl Foundation began trapping mammalian meso-predators in North Dakota during the breeding season in an attempt to increase waterfowl nest success and enhance recruitment into the fall flight and subsequent breeding population. Multiple studies on these sites demonstrated that removing predators results in near doubling of nest success, which previous simulation modeling suggests is the most influential vital rate influencing the population growth rate of mid-continent mallards (Anas platyrhynchos). We present an assessment of the impact of predator removal on mallard production using population models. We conducted this study on 9 township-sized (93.2 km2) sites (4–8 sites annually per vital rate) in northeastern North Dakota from 2006–2008. Trappers removed mammalian meso-predators on 5 sites and the other 4 served as unmanaged reference sites. To estimate recruitment, we used derived estimates and process variance of pair numbers, hen success (nest survival corrected for renesting), initial brood size, pre-fledging survival, and post-fledging survival, along with previously published estimates of breeding propensity and adult female survival rates. Trapped sites had greater hen success (H = 0.69, equation image = 0.03) than reference sites (H = 0.53, equation image = 0.06), but similar indicated breeding pairs, initial brood size, and pre-fledging survival. We estimated that females on trapped sites added 140 more mallards of both sexes to the fall flight than females on reference sites, at an approximate cost of $74.29 per incremental mallard. Additionally, trapping predators provided a marginal increase (0.04) in finite population growth. We found that predator removal targeted at mammalian nest predators did not produce as many incremental mallards as previously thought and may not be a viable strategy for increasing mallard productivity under conditions similar to those observed during this study. We conducted a sensitivity analysis and determined that pre-fledging survival was the most influential factor regulating mallard population growth. Although hen success increased as a result of trapping, duckling survival became a limiting factor. We suggest that waterfowl managers assess multiple vital rates to determine the likelihood that management actions focused on a single parameter, such as nest success, will yield desired population level effects. © 2012 The Wildlife Society.

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