Bald eagle space use and diets on the California Channel Islands as determined by GPS and stable isotopes

Includes bibliographical references (leaves 78-87)Bald Eagles have been the subject of intensive studies throughout North America in part due to their recent status as an endangered species. Bald Eagles were reintroduced to the California Channel Islands beginning in 1980 on Santa Catalina Island and in 2002 on the Northern Channel Islands. These islands are unique in their geographic setting and their species compositions. Prior to their reintroduction on the Channel Islands, little was known about the space use and diets of Bald Eagles on these islands. These are important to understand in relation to existing and future management strategies. I studied Bald Eagle space use using GPS data in a GIS, and diets using stable isotopes on the California Channel Islands. The space use of immature Bald Eagles equipped with GPS transmitters was monitored through GPS data collection, and space use patterns were investigated using the program LoCoH (Local Convex Hull) to determine 50% core use areas and 95% home range areas in relation to year, season, proportion of use of different islands, and use of interior versus shoreline locations. Space use patterns varied with year, season, island, and location. Immature Bald Eagles shifted their space use from the larger islands of Santa Cruz Island and Santa Rosa Island to the small island of Anacapa, especially in the spring and summer in Years 3 and 4 (2005/06 - 2006/07). This shift may have been due to changes in available food resources over time. In the first 2 years of the study, feral pig carcasses were available year-round on Santa Cruz Island. A pig eradication project was completed between spring 2005 and summer 2006 which may have resulted in immature Bald Eagles using other areas (i.e., Anacapa Island) to find food. Immature Bald Eagle diets varied over time based on the stable isotope data for recaptured Bald Eagles. Immature Bald Eagle isotopic signatures spanned the isotopic gradient created between the marine and terrestrial signatures of their marine and terrestrial food sources