Doctor of Philosophy (PhD)


Renewable Natural Resources

Document Type



I tested the scope of the Spring Condition Hypothesis in explaining the continental population decline of lesser scaup (Aythya affinis; hereafter scaup) and explored potential mechanisms affecting female body condition to assist conservation efforts for population recovery. Lipid reserves of females currently are lower than historical values during spring migration throughout Iowa, Minnesota, and North Dakota; females catabolized lipids throughout this area (indexed by concentrations of plasma-lipid metabolites, which accounted for 75% of the variation in mass change). My results indicate that a large segment of the continental scaup population likely is affected by decreased lipid reserves, which could cause reductions in breeding propensity and reproductive success. Hepatic cadmium was negatively correlated with lipid reserves of females during spring migration; however, current cadmium concentrations only accounted for 11% of the observed decrease in lipid reserves of females between Illinois and Minnesota. Wetland use by scaup was positively correlated with amphipod densities throughout the upper-Midwest, indicating a preference for amphipods. Amphipod densities were markedly lower (1 - 12 m-3) and scaup were consuming fewer amphipods in the upper-Midwest relative to historical records. Scaup probably must spend more time searching for food within and among wetlands than they did historically. Fish occurred in 74, 78 - 84, and 31 - 45% of wetlands in Iowa, Minnesota, and North Dakota, respectively, whereas historically they occurred in only 10 - 20% of wetlands. Amphipod densities were negatively correlated to fish densities and sedimentation. My results indicate that there has been a decrease in amphipod densities throughout the upper-Midwest, which likely is causing the observed decreases in lipid reserves of scaup. My results generally were consistent with the Spring Condition Hypothesis and indicate that wetland restoration efforts are needed throughout the upper-Midwest, but especially in Iowa and southern Minnesota. Managers should provide abundant populations of amphipods (over 26 m-3 geometric mean across the landscape) and target wetlands that: (1) have large (> 500 m diameter) open-water zones, (2) are deep enough to support over-wintering populations of amphipods, (3) allow management of fish communities, and (4) the surrounding land can be managed to reduce sedimentation.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Alan D. Afton