American black duck (Anas rubripes) populations declined throughout North America from 1950–1990, but the breeding population since has stabilized. However, limited information exists on black ducks in the Mississippi Flyway, where wintering populations continue to decline. I radiomarked 111 female black ducks at Tennessee National Wildlife Refuge (TNWR) in winters 2010–2012 to estimate winter survival and investigate patterns of habitat selection. Winter survival (83–85%) was greater than or comparable to previous estimates for black duck populations in North America. Interval survival increased 0.6% with a 100 g increase in body mass, but survival differed between years and waterfowl hunting seasons relative to body mass. Black ducks selected habitats on TNWR and emergent/scrub-shrub wetlands throughout winter regardless of hunting season or time of day. High winter survival rates and consistent use of TNWR suggest the refuge provides an important complex of habitats for black ducks wintering in Tennessee.

The behavioral ecology of the American Wigeon (Anas americana) was studied over its annual cycle in western Canada between 1974 and 1978. The objective of this work was to examine the cross-seasonal interactions of the biology and behavior of the wigeon as they underlie the evolution of its mating system. The wigeon was more herbivorous than any other dabbling duck studied so far and spent a considerable amount of time feeding in upland habitats. Vegetation was important in the diet year round but particularly from late summer through the winter. Plant seeds were a rich source of protein and carbohydrate early in the spring. During breeding stages animal foods were selected by wigeons, particularly females. Wigeons usually did not feed on small crustaceans and gastropods but selected larger aquatic insect foods. Relative to other Anas soecies, the wigeon has a goose-like bill whose structure facilitates feeding on upland and aquatic vegetation. With the evolution of this specialization, efficient surface-straining of small foods has been sacrificed. To increase food digestibility, wigeons altered gizzard grit composition and organ sizes. Through these mechanisms I have demonstrated how wigeons have been able to increase the efficiency of digestion.

The behavioral ecology of the American Wigeon (Anas americana) was studied over its annual cycle in western Canada between 1974 and 1978. The objective of this work was to examine the cross-seasonal interactions of the biology and behavior of the wigeon as they underlie the evolution of its mating system. The wigeon was more herbivorous than any other dabbling duck studied so far and spent a considerable amount of time feeding in upland habitats. Vegetation was important in the diet year round but particularly from late summer through the winter. Plant seeds were a rich source of protein and carbohydrate early in the spring. During breeding stages animal foods were selected by wigeons, particularly females. Wigeons usually did not feed on small crustaceans and gastropods but selected larger aquatic insect foods. Relative to other Anas soecies, the wigeon has a goose-like bill whose structure facilitates feeding on upland and aquatic vegetation. With the evolution of this specialization, efficient surface-straining of small foods has been sacrificed. To increase food digestibility, wigeons altered gizzard grit composition and organ sizes. Through these mechanisms I have demonstrated how wigeons have been able to increase the efficiency of digestion.

Influenza A viruses cause seasonal and pandemic outbreaks that range from mild infections to the disastrous Spanish Flu. Resistance to neuraminidase inhibitors (NAIs) is a growing problem as these drugs constitute a vital part of treatment strategies and pandemic preparedness plans worldwide. Oseltamivir (Tamiflu®) is the mostly used NAI. Its active metabolite, oseltamivir carboxylate (OC), is excreted from treated patients and degrades poorly in sewage treatment plants and surface water. Thus, OC can enter aquatic environments where the natural influenza reservoir, dabbling ducks, can be exposed to the substance and resistance could develop. If NAI resistance is established in influenza viruses circulating among wild birds, the resistance can form part of a virus re-entering the human population either by reassortment or by direct transmission. In this thesis, evidence is presented that OC is present in the waterways during a seasonal influenza outbreak in Japan, a country in which oseltamivir is liberally used. Furthermore, when mallards were infected with an influenza A/H1N1 virus and subjected to low, environmental-like concentrations of OC, resistance developed through acquisition of the well-known resistance mutation H274Y. The influenza infection in the mallards was mainly intestinal, had a rapid onset and was progressing in a longitudinal fashion in the intestine. Finally, influenza A viruses isolated from wild mallards in Sweden and containing resistance-related mutations were examined by a neuraminidase inhibition assay. The viruses did not have a decreased sensitivity to NAIs, but had mutations with a resistance-enhancing potential. Thus, OC is present in the environment and environmental-like concentrations of OC induce resistance in influenza viruses of dabbling ducks. The present resistance situation among wild birds is not well understood but the existence of H274Y among wild birds, though rare, and the spread of the former seasonal A/H1N1 virus containing H274Y among humans indicate that resistance mutations could establish themselves also among wild birds. An oseltamivir-resistant pandemic or a human-adapted highly-pathogenic avian influenza virus are frightening scenarios as oseltamivir is a cornerstone in the defense in those situations. There is a need for further studies, surveillance in wild birds and for a prudent use of antivirals.

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