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Wind energy is an important sector of the renewable energy market. Observations of bat fatalities at wind farms raise concern about impacts to biodiversity, particularly amid projections of wind energy build-out. We investigated how continued wind energy development in the United States and Canada, as well as adoption of measures to reduce bat fatality rates, influence the population viability of the hoary bat (L. cinereus). Our model included uncertainty about population size and dynamics as well as future wind energy development. Results indicate that current levels of wind energy build-out may have already caused substantial population declines. Under our lowest-risk scenario of high maximum growth rate and low wind energy build-out, the median simulated population of 2.25 million hoary bats experienced a 50% decline by 2028. We show that risks of decline and extinction may still be mediated with rapid adoption of measures to reduce bat fatalities. We find that levels of fatality reduction shown to be achievable in empirical studies of fatality minimization, by turbine curtailment, may be sufficient to manage risks. Simulations of population trends suggest that declines exceeding 5% per year support fatality reduction to manage extinction risk. Importantly, both the risks and the level of fatality reduction necessary to manage them were highly uncertain. Population size remains the most critical data gap to determining population viability of hoary bats. Studies to empirically determine baseline estimates of population size and trends over time remain urgently needed to inform conservation action. [ABSTRACT FROM AUTHOR]