Conditioning Fledgling Bonelli's Eagles (Aquila fasciata) to Avoid Power Line Pylons

ABSTRACT. Throughout Europe, electrocution on distribution power lines is the main cause of mortality for fledgling Bonelli's Eagles (Aquila fasciata) released into the wild through hacking. To attempt to reduce electrocutions, we subjected 17 fledglings that had not previously had any contact with power line pylons to aversive conditioning. To this end, we installed electrified barrier wires on two distribution pylons (one each of the two most common pylon types in northern Spain), which were disconnected from the electric grid. The electrified barriers, which were in place from 2020 through 2022, lightly shocked fledglings alighting on them. We compared the subsequent behavior of conditioned fledglings with that of a control sample of 19 unconditioned fledglings released between 2015 and 2019. The results suggest that conditioning results in (1) a delay in juveniles' use of distribution power line pylons as perches in the wild; (2) juveniles' avoidance of pylons in temporary settlement areas; and (3) a nonsignificant increase in juvenile survival rates during the first year of life. This approach may have applicability in other population reinforcement projects, and in areas with high concentrations (communal roosts and vulture restaurants) of other large raptors.