Strategies for Mitigating Impacts to Aerofauna from Offshore Wind Energy Development: Available Evidence and Data Gaps

A diversity of approaches exist for mitigating (e.g., avoiding, minimizing, or compensating for) the effects of offshore wind energy (OSW) development on birds and bats, but little is known about the effectiveness of many of these approaches. To address this knowledge gap, we reviewed the scientific and gray literature to evaluate the evidence base for potential bird- and bat-related mitigation approaches for OSW, including studies from other industries where relevant (e.g., terrestrial wind energy, offshore oil and gas industry). Of a total of 219 mitigation approaches, most focused on minimization, with far fewer addressing avoidance or compensation. Sixty-five percent had no evidence of testing. Of the 76 mitigation approaches that were field tested or implemented, we found evidence of effectiveness for only 40 approaches, of which only 10 were specific to the OSW sector. Consequently, a majority of all the mitigation approaches for birds (82%) and bats (89%) lacked any evidence of effectiveness. For birds, minimization approaches related to lighting reduction were the most tested and effective methods for reducing maladaptive attraction and collisions. For bats, minimization approaches involving adjustments to turbine operations (e.g., curtailment of turbine blades) were most tested and effective methods for reducing collisions. Given the limited evidence of effectiveness for most mitigation approaches, assuming their success systematically underestimating project-level and cumulative impacts, underscoring the need to prioritize avoidance, consistent with the mitigation hierarchy, and rigorously test mitigation approaches for birds and bats in offshore environments. RESUMEIl existe une diversite dapproches pour attenuer (e.g. eviter, minimiser ou compenser) les effets du developpement de l lEnergie Eolienne Extracotiere (EEE) sur les oiseaux et les chauves-souris, mais lefficacite de nombreuses de ces approches est encore peu connue. Pour combler ces lacunes, nous avons passe en revue la litterature scientifique et la litterature grise afin devaluer les donnees probantes concernant les mesures dattenuation potentielle pour lEEE et les oiseaux et les chauves-souris,, inclus des etudes dautres industries lorsque cela etait pertinent (e.g., lenergie eolienne terrestre, lindustrie petroliere et gaziere extracotiere). Sur un total de 219 approches dattenuation pertinentes pour lEEE, la plupart des approches se concentraient sur la minimisation, avec beaucoup moins dapproches portant sur levitement ou la compensation. Soixante-et-un pourcent des approches proposees ne semblent pas avoir ete testees. Parmi les 76 approches dattenuation qui ont ete testees sur le terrain ou mises en uvre, nous avons trouve des preuves de leur efficacite pour seulement 40 approches, dont seulement 10 etaient specifiques ale secteur de lEEE. Par consequent, la majorite des approches dattenuation pour les oiseaux (82 %) et les chauves-souris (89%) ne disposaient daucune preuve defficacite. Chez les oiseaux, les approches de minimisation liees a la reduction de leclairage etaient les methodes les plus couramment testees et les plus efficaces pour reduire lattraction et les collisions. Chez les chauves-souris, les approches de minimisation impliquant la modification du fonctionnement des turbines (e.g., reduction de la vitesse de rotation ou mise en drapeau des helices) etaient les methodes les plus couramment testees et les plus efficaces pour reduire les collisions. Compte tenu des preuves limitees de lefficacite de la plupart des approches dattenuation, le fait de presumer de leur succes conduit a une sous-estimation systematique des impacts a lechelle des projets et des impacts cumulatifs, ce qui souligne la necessite de privilegier levitement, conformement a la hierarchie dattenuation, et de tester rigoureusement les mesures dattenuation pour les oiseaux et les chauves-souris en milieux offshore. IMPLICATIONS FOR MANAGERSO_LIBased on our literature review of potential mitigation approaches for birds and bats in relation to offshore wind development, most approaches remain untested or lack evidence of effectiveness (bats - 89%, birds - 82%). C_LIO_LIMost minimization approaches have primarily been tested in the terrestrial context, leaving important questions regarding the transferability of these results to the offshore environment. C_LIO_LIGiven the limited evidence of effectiveness for most mitigation approaches, assuming their success systematically underestimates project-level and cumulative impacts, underscoring the need to prioritize avoidance and rigorously test mitigation approaches for birds and bats in offshore environments. C_LI