Human impacts on the ecology of bald eagles in interior Alaska Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m900nz88f

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  • To assess the consequences of increased recreational activity on bald eagles (Haliaeetus leucocephalus), we studied factors that influenced their behavior and reproductive success in the Gulkana River basin, Alaska, from 1989 to 1993. Both extrinsic and intrinsic factors were associated with reproductive success. Productivity averaged 0.86 young fledged per occupied territory (SE = 0.05) with 59% nest success (n = 274), but productivity varied among years and subdrainages (P < 0.02). Further, productivity and nest success, but not density, of pairs along the river corridor were negatively associated with levels of human activity (P = 0.037). Pairs that were successful one year were more likely to occupy the same territories, less likely to change nest locations within a territory, more likely to be successful, and fledged more offspring the following year compared to pairs that were previously unsuccessful. Most nesting failure (92%) occurred during incubation. Annual and regional variability in reproductive success of northern bald eagle populations may result from susceptibility to severe spring weather conditions during incubation. Behavior of breeding eagles changed when humans camped near ( 100 m) versus far ( 500 m) from nests (P = 0.0036). Adults decreased the time they fed nestlings and themselves (-30%), preened (-53%), slept (-5 6%) and maintained nests (-50%), but increased the time they brooded nestlings (14%). Further, adults decreased the frequency with which they performed most nesting behaviors, including the amount of prey they consumed at nests (-26%) and fed to nestlings (-29%). Our results show that human activity near nests altered breeding behavior, and suggest that if disturbances in nesting territories were sustained, eagle populations could be affected adversely. The context in which human-eagle encounters occurred affected eagle responses to boating activity. The distance a disturbance was first visible to eagles, the distance they perched from the river, perch height, eagle age, julian date, and ambient temperature were among those factors that influenced both flush response and flush distance of nonbreeding eagles. Breeding adults were less likely to flush and flushed at shorter distances (87.5 ± 10.2 m) than nonbreeding adults (113.0 ± 4.5 in) to approaching boats (P < 0.024). Based on our studies, we recommend a series of strategies to minimize the adverse effects of human activity on breeding and nonbreeding eagles.
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