Wind farms have been shown to cause bird mortality in many studies. Proposals for the development of wind farms in Lesotho, which is core habitat for small and declining populations of the regionally Endangered Bearded Vulture Gypaetus barbatus meridionalis and regionally and globally Vulnerable southern African endemic Cape Vulture Gyps coprotheres is therefore of concern. We use satellite tracking data to demonstrate that southern African Bearded Vultures spend the majority of their time foraging in landscape zones typically chosen for wind farm development (active selection for ridge tops and upper slopes), and that both species generally fly at heights within the rotor-sweep of a typical, modern wind turbine. We constructed a population viability model using actual population data from the area presently being targeted by the wind energy industry, calibrated with actual data on local population trends, to assess the potential impact of two specific wind farm development proposals on the populations of both vulture species. Even under conservative assumptions, relatively small-scale wind farm development in the Lesotho Highlands is likely to result in accelerated population decline and extinction in both species. The only feasible mitigation is to move the development sites off the ridge tops and upper slopes.