Abstract
As wind-energy development continues to expand globally to help slow impacts from climate change, so does the need to mitigate impacts to birds from collisions with wind turbines. DTBird is an automated detection, audio deterrent, and turbine curtailment system designed to discourage birds from entering the rotor-swept zone (RSZ) of spinning wind turbines. With Golden Eagles (Aquila chrysaetos) a primary species of interest, we summarize the behavioral responses of a suite of large soaring raptors exposed to DTBird audio deterrents (approximate broadcast volume 117–121 dB at 1 m and generally <40 dB at 330–350 m). We quantify the probability of effective deterrence and describe variation in deterrence effectiveness related to study sites (two commercial facilities, one in California and one in Washington, USA), species groups (eagles, vultures, and buteos), wind speed, and risk of collision before deterrent triggering. Generalized linear modeling indicated: (1) lower probability of effective deterrence (PED) for all species groups in Washington; (2) positive relationship between PED and wind speed for eagles and vultures, but a negative relationship for smaller buteos; and (3) higher PED for raptors at high and especially moderate risk of exposure prior to deterrent triggering than for those at low risk. Among probable (confirmed and suspected) Golden Eagles (n = 158), 79% in California and 61% in Washington responded to deterrents in a way that likely reduced their risk of entering the RSZ of spinning turbines. Probable Turkey Vultures (n = 127; Cathartes aura) and buteos (n = 229; primarily Buteo jamaicensis and B. lagopus) responded similarly, whereas Bald Eagles (n = 40; Haliaeetus leucocephalus) more often responded positively in Washington (species mostly absent in California). The Washington assessment also uniquely supported a control-treatment design to distinguish the deterrence effects of spinning turbines alone versus spinning turbines plus audio deterrents. This analysis confirmed that broadcasted audio deterrents generally at least doubled the probability of effective deterrence compared to spinning turbines alone. Stated another way, the percentage of raptors that showed no response was much lower when the deterrents were broadcasted (treatment group; 27%) than when the deterrents were muted (control group; 65%). Our study results indicate that DTBird audio deterrents can be effective in discouraging Golden Eagles and other large soaring raptors from approaching the RSZ of spinning turbines.