Date of Award
Master of Science
Wildlife and Fisheries Science
Matthew J. Gray
Heath M. Hagy, Craig A. Harper, J. Brian Davis
American black duck (Anas rubripes) populations declined throughout North America in the late 20th century. Although the breeding population has since stabilized, research investigating habitat use by black ducks in the Mississippi Flyway is scarce. Impacts of wetland management practices in response to invasive species must also be tested to measure responses to habitat quality by black ducks and other waterfowl. During winters 2011-2013 (December-February), I estimated food biomass, diurnal habitat use, and activities of black ducks in 6 cover types at the Duck River Unit of Tennessee National Wildlife Refuge and Cross Creeks National Wildlife Refuge in western Tennessee. I also evaluated vegetation response, dabbling duck use and activities, and food biomass in moist-soil wetland plots containing alligatorweed (Alternanthera philoxeroides) treated with imazapyr. Black ducks were most common in scrub-shrub wetlands, where locomotion and resting behaviors were dominant activities. Although highly variable, black duck use was also high in unharvested, flooded corn. Moist-soil wetlands and mudflats were important foraging substrates, but black duck use in these areas were not equivocal to use in scrub-shrub. Greatest food biomass occurred in moist-soil wetlands compared to other cover types. However, black ducks appeared to select sites with lesser, but consistent food densities throughout winter. Waterfowl use, behavior, and food biomass did not differ between control and treatment plots. Reductions of alligatorweed with imazapyr in moist-soil wetlands did not improve use of those sites by black ducks perhaps due to a lack of shrub cover. My results suggest cumulative life-history strategies likely influence habitat use by wintering American black ducks. Managers should provide foraging areas proximate to scrub-shrub wetlands to benefit black ducks in western Tennessee. Flooded agriculture at TNWR and CCNWR could facilitate interactions and consequently hybridization potential between mallards and black ducks. Managers should reduce flooded corn acreage and restore scrub-shrub wetlands amidst early succession emergent wetlands. Imazapyr treatment should not replace current management strategies in moist-soil wetlands (i.e., rotational disking, disking with supplemental planting, prescribed burning), but may be used to control invasive plant species as needed without negative implications on food resources for wintering waterfowl during treatment years.
Osborn, Joshua Matthew, "American Black Duck Wintering Dynamics and Dabbling Duck Response to Herbicide Application in Western Tennessee Wetlands. " Master's Thesis, University of Tennessee, 2015.