Bats are particularly susceptible to anthropogenic changes because of their low reproductive rate, longevity, and high metabolic rates (Voigt and Kingston 2016), limiting their ability to recover from declines (Barclay and Harder 2003). Bat fatalities due to wind turbines raise serious concerns about population-level impacts (Barclay and Harder 2003; Frick et al. 2017). In addition to natural and other forms of anthropogenic-induced mortality, wind turbine mortality further compounds population declines for many species of bats and warrants mitigation (Arnett et al. 2016). In the USA, the hoary bat (Lasiurus cinereus), a once widespread and abundant species, is under serious threat due to wind energy and is facing population declines (Frick et al. 2017). In an effort to prevent or reduce bat population declines in South Africa (SA), these guidelines propose setting a cap or limit on bat fatalities at wind energy facilities.
Due to the difficulty in determining actual bat population sizes (Lentini et al. 2015; Arnett et al. 2016), this guideline document uses available data, such as the size of development sites and the bat activity indices (median bat passes per recording hour) associated with the 12 ecoregions (MacEwan et al. 2020) as an indication of the bat occupancy of an area, to determine appropriate fatality thresholds that aim to prevent bat population level losses per species or per family group depending on the level to which bat carcasses have been identified to, i.e. to prevent cumulative impacts on bat populations within an ecoregion.
When empirical data is lacking for focal species, data from similar species or structured elicitation of expert opinion can be used for conservation decision-making (Burgman et al. 2011; Drescher et al. 2013; Martin et al. 2012). Such expert elicitation has been used for a variety of conservation problems (Donlan et al. 2010; Martin et al. 2005; Runge et al. 2011; Smith et al. 2007). Deciding whether conservation measures are necessary to prevent or mitigate impacts from wind energy development on populations of bats requires use of expert judgments and/or use of data from similar taxa to quantify reasonable scenarios of population growth and losses (Frick et al. 2017).