Experimental effects of human activity on breeding bald eagles

To assess the consequences of increased recreational activity in wilderness areas, we studied the effects of human activity on breeding behavior of Bald Eagles (Haliaeetus leucocephalus) in interior Alaska. Activity budgets of breeding eagles changed considerably when humans were camped for 24 h at a distance of 100 m from nests (treatment) compared to when they were camped 500 m from nests (control) (P = 0.0036). With humans near nests, adult eagles decreased the time they preened (percentage change from control to treatment = -53%), slept (-56%), maintained nests (-50%), and fed themselves and their nestlings (-30%) and increased the time they brooded nestlings (+14%). Further, overall activity (total number of behaviors performed by adults at nests per day) decreased by 27% with humans near nests, as did the amount of prey adults consumed (-26%) and fed to nestlings (-29%). In contrast, nest attendance did not change with humans near nests (percentage change = 0.3%, P = 0.9); however, the time adults were absent from the nest area (≥200 m from nests) increased by 24% with humans near nests (P = 0.013). Throughout 24-h treatments, eagle responses to nearby humans diminished, suggesting that eagles habituated to the disturbance. During the last 4 h of treatment, however, adults still vocalized twice as frequently as controls, indicating continued agitation. Human activity near nests caused clear and consistent changes in behaviors of breeding eagles, suggesting that frequent human activities near nests could adversely affect nestling survival, and therefore reproductive success.