The surf scoter, Melanitta perspicillata, is a declining sea duck species that relies on multiple habitats for wintering, breeding, and migrating. Conservation of this species may depend on understanding and protecting networks of critical habitats, including those in urban estuaries. I examined habitat use and movements of scoters at several spatial and temporal scales, and evaluated the influence of an invasive species on diet, contaminant accumulation, and body condition, focusing particularly on birds wintering in San Francisco Bay (SFB).
I compared spring migration routes, chronology, and stop-over sites among satellite-marked surf scoters from four wintering estuaries along the Pacific coast. Eighty-three percent of scoters followed two distinct routes to the breeding area. Route choice was related to nesting site latitude in the Canadian Northern Boreal Forest. Scoters had strong route fidelity, but altered chronology and stopovers between years. Departure date varied by wintering site, but arrival and apparent settling dates were synchronous.
I modeled relationships between environmental variables and scoter occurrence and density, and determined distributions and movements of radio-marked surf scoters in SFB. Herring roe was the strongest predictor of scoter presence and density; however salinity, depth, and eelgrass presence also ranked highly. Scoters restricted their movements and used small areas within the marine Central Bay later in winter, potentially related to prey depletion elsewhere.
I evaluated the role of an invasive bivalve, Corbula amurensis , in nutrient acquisition and contaminant accumulation in SFB surf scoters. Scoter diets were dominated by Corbula in the northern estuary, and Japanese littleneck clam, Venerupis philipinarium, and Pacific herring, Clupea pallasi, roe in the Central Bay. Scoter lipids were negatively correlated to δ15Nplasma and positively correlated to δ 13Cmuscle, suggesting bivalves contributed more to lipid acquisition than other prey, and scoters foraging on Venerupis versus Corbula attained higher lipids. Selenium concentrations were similar between Corbula and Venerupis. Stable isotope mixing models indicated higher selenium concentrations in North Bay scoters were related to the proportion but not the species of bivalves in diet. I found little effect of selenium, cadmium or total mercury on scoter lipid or protein content.
|Advisor:||Miles, A. Keith, Eadie, John M.|
|Commitee:||Johnson, Michael L.|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 71/12, Dissertation Abstracts International|
|Subjects:||Wildlife Management, Ecology, Conservation|
|Keywords:||Corbula amurensis, Estuaries, Habitat modeling, Melanitta perspicillata, Sea ducks, Selenium, Stable isotopes|
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