The Emerging Conflict of Common Ravens Roosting on Electric Power Transmission Line Towers in Montana, USA

: Bird interactions with electric power lines can cause faults (e.g., disruption of electrical service). Faults on 500kV transmission lines in Montana, USA, which are integral to the Northwest USA power grid, became concerning during winter 2016–2017. In 2017 we found insulators contaminated with bird droppings and discovered a large nocturnal roost of common ravens ( Corvus corax ). To assess the potential magnitude of the impact of raven roosts on electric power transmission, we summarized fault data obtained from the Energy Management System and raven abundance data obtained from the Christmas Bird Count in central Montana from 2005 to 2020. We also conducted counts at 7 roosts in the study area in winter 2019–2020. We detected a positive relationship between the number of faults reported and raven abundance. The 3 largest roosts we surveyed peaked at 1,000–1,500 ravens on single evenings. The number of faults reported in winter 2019–2020 decreased after use of silicon-coated insulators, perch deterrents, and periodic washing of insulators. Increased raven populations throughout their range may cause similar conflicts for other electric utilities. Long-term management of ravens will need to integrate approaches at both local and landscape scales.