| Summary: | Typescript (photocopy). Habitat factors, feeding ecology, and physiological body condition of northern shovelers (Anas clypeata) were studied on saline wetlands of the Texas Gulf Coast, and on several freshwater lakes 18 km inland. The hypothesis considered was that freshwater and saltwater habitats do not provide equal resources for wintering shovelers and that this difference would be reflected in body condition. Aquatic vegetation persisted through winter 1982-84 in freshwater wetlands, but died out of most saltwater ponds by late December both years. Plankton biomass averaged 4x greater in freshwater than saltwater habitat during winter 1982-83, but little difference occurred the next year. Nekton and seed biomass averaged 33% and 4x greater, respectively, in freshwater habitat during 1982-84. Shovelers fed about equal time on freshwater and saltwater habitats. Plankton comprised about 33% of the diet in both habitats, but shovelers that inhabited freshwater consumed proportionately more plant foods than their saltwater counterparts, which presumably substituted a low-quality diet of Foraminifera. Gut morphology data indicated clearly that diet quality was better among shovelers that foraged on freshwater wetlands. However, the caloric density of the diet was about equal on freshwater and saltwater habitats in 1982-83 and greater on saltwater the next winter, due largely to consumption of cold-stunned fish during a 2-week period in December 1983. Plankton was the most preferred shoveler food on both wetland types. Average body and omental-fat weights of shovelers of all age-sex classes were larger at freshwater than saltwater sites in 29 of 40 between-habitat comparisons; a notable exception to that trend occurred during the record cold weather of 1983-84. Average body, omental-fat, and sternal-muscle weights were larger at saltwater sites, apparently due to consumption of fish. In contrast, during the unusually cold weather, condition declined in freshwater habitat, presumably because of the lack of fish ...
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