Date of Graduation

12-2021

Document Type

Thesis

Degree Name

Master of Science in Biology (MS)

Degree Level

Graduate

Department

Biological Sciences

Advisor

Brett A. Degregorio

Committee Member

Dan D. Magoulick

Second Committee Member

Luke W. Naylor

Third Committee Member

David G. Krementz

Keywords

Body Condition, Body Mass, Ecology, Waterfowl, Wildlife Conservation, Wildlife Management

Abstract

Most North American waterfowl overwinter in southern North America before migrating back to breeding grounds in the northern US and Canada. These species face the challenge of needing to maintain or increase their body mass during an environmentally difficult winter period. Successful body mass maintenance during the winter period has major ramifications not only for their winter survival but for their fitness across the entire year. Recent research in Europe and the western United States suggests that the body mass of mallards (Anas platyrhynchos) has increased from the late 1960s to early 2000s. However, the factors responsible for increases in mallard body mass remain unknown. Because research has shown that mallard body mass and condition is directly proportional to energy acquired across the landscape, conservation agencies attempt to provide high-energy habitat such as woody wetlands, herbaceous wetlands, and open water areas for waterfowl to feed, rest, and complete other important life-cycle activities. Additionally, managers have tried to increase the amount of flooded agricultural grain across the landscape, as crops like rice can provide waterfowl with a source of high-energy food, especially in important overwintering waterfowl areas such as the Lower Mississippi Alluvial Valley (LMAV). However, long-term trends in mallard body mass, as well as the relationship between body condition of mallards and landscape composition has yet to be assessed in the LMAV. To assess mallard body mass over time in the LMAV, we collected measurements from hunter-harvested mallards across the LMAV of Arkansas and Mississippi during duck hunting seasons from 1979-2021. We measured body mass, wing length, and aged and sexed each bird. We then developed four age-sex linear mixed effects models (LMM) analyzing changes in body mass across years. We also analyzed body mass within a winter period across the day of duck season, as well as in relation to cumulative rainfall, river flooding, and a weather severity index (WSI). We determined that mallard body mass has increased within the LMAV from 1979-2021. Within years, body mass generally decreased over the course of the hunting season. Mallard body mass generally increased when rainfall and river flooding increased. However, there was generally no relationship with mallard body mass and WSI. Using Arkansas mallard measurements from duck hunting seasons 2019-2020 and 2020-2021, we calculated body condition indices (BCI) for each bird using the residuals from a mass by wing length regression for each age-sex class. We then used an LMM to analyze changes in mallard BCI in relation to landscape variables known to influence mallard body mass or BCI within a 30-km radius of each harvest site. Landscape variables included proportion of water cover, rice, soybeans, woody wetlands, herbaceous wetlands, open water areas, and areas of human disturbance. We found that mallards with high BCI came from areas with higher proportions of water cover, woody wetlands, and open water. However, mallards with lower BCI came from areas with higher proportions of herbaceous wetlands and human disturbance. We suggest managers restore, protect, and increase food resource availability in wetlands including bottomland hardwood forests.

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