AUTHORS: Bram H. F. Verheijen, Missouri Cooperative Fish and Wildlife Research Unit, University of Missouri; Elisabeth B. Webb, U.S. Geological Survey, Missouri Cooperative Fish and Wildlife Research Unit, University of Missouri; Michael G. Brasher, Ducks Unlimited, Inc.; Heath M. Hagy, Habitat and Population Evaluation Team, U.S. Fish and Wildlife Service
ABSTRACT: Geographical distributions of migrating and wintering ducks are likely influenced by climate, habitat availability, and land use. Shifts in wetland availability related to changes in climate, land use, and other factors could lead to temporal mismatches in habitat provision and harvest management decisions if informed by historical duck distributions. Earlier research reported that centroids of mallard (Anas platyrhynchos) band recovery distributions moved north by >550 km in December and January for some subpopulations between 1960–2019. To identify potential causal mechanisms underlying these changes, we used band recovery data from 1984–2019 and tested relative effects of several weather and land use variables on changes in mallard band recovery distributions over time. Preliminary results for January recoveries show that weather variables have greater effects than land use variables on average band recovery distributions and long-term changes therein. Relative density of band recoveries per hunting day increased with precipitation, cropland cover, and wetland cover, decreased with number of frost days, snow depth, and urban land cover, with the greatest band recovery densities observed at intermediate values of minimum temperatures. When explaining long-term changes in band recovery distributions, we found that areas into which recoveries expanded in the 2010s experienced greater increases in temperature (0.8 vs. 1.1°C) and cropland cover (0.1 vs. 1.0%) than areas abandoned since the 1980s, whereas changes in other covariates were minimal. Distributional changes could alter the timing of local habitat management decisions and possibly reduce hunting and recreational opportunities in southern states. Climate, land use, and changes in breeding populations likely all influence autumn and winter distributions of ducks. Understanding temporal, interspecific, and intraspecific variation in waterfowl distributions and its drivers will help inform future conservation and management at broad geographic scales.
