The human enterprise continuously faces the need for increased energy, particularly electrical. The main sources for electricity production, until a few years ago, have been fossil fuels or hydroelectric dams. In recent times generation from other renewable sources has increased, among which wind energy production has become increasingly important (GWSC 2014). In contrast to fossil fuels, energy produced by wind turbines entails no CO2 production or any other type of air pollution (Fthenakis and Kim 2009). Therefore, in this time of global warming, a massive increase in wind farms is expected to contribute to a cleaner energy future (GWSC 2011), along with other renewable energy sources (IPCC 2007). Projections are that wind energy production will increase exponentially from 6.1 gigawatts (GW) per year in 1996 and 318.1 GW in 2013 (GWSC 2014). See Table 1 for projections of the growth of the industry to 2030.
Recent studies have hypothesized that wind farm facilities can have a highly negative impact on the local community of bats (Rydell et al. 2010; Arnett and Baerwald 2013; Hayes 2013; Medellín et al. 2014). The tree roosting bat species seem to be those that have high fatalities by the turbines (Cryan et al. 2014). Two of these studies have been very controversial. The first of these (Subramanian 2012) reported that 18,000 wind turbines in Spain may be killing between 6 to 18 million birds and bats annually. The second one (Hayes 2013) has analyzed 22 published estimates of bat mortality at wind farms in the United States which ranged from 0.2 to 53.5 fatalities per megawatt (MW) generated per year with a mean of 13.4. At the 2012 rate of 51,000 MW per year, he suggests that over 600,000 bats would have been killed in that year. The reliability of these mortality extrapolations has been criticized on statistical methodology grounds (Huso and Dalthorp 2014), but what is important here is that these and other studies have shown that significant numbers of bat fatalities are caused by wind turbines in the United States alone. Moreover, we must keep in mind that mortally injured bats can fly away only to die later causing underestimation of mortality rates (Grodsky et al. 2011). Some data show that bats are more vulnerable to die by wind turbines than birds (Smallwood 2013).
This non-trivial impact on bat mortality carries potentially substantial ecological and agricultural costs. Bats are abundant in temperate to tropical regions, including semi-arid biomes. They are known to have major impacts in controlling insect pests of agriculture at least in some regions (Boyles et al. 2011). Furthermore, frugivores are often important seed dispersers and significant pollinators as well. There is also the potential for bats killed by wind turbines to spread rabies to scavengers (Grodsky et al. 2011). This conflict between the needs for clean electricity production and the needs for bat conservation must be addressed promptly.
Given that wind power generation is a necessary component of our future power supply, that bats are major contributors to ecosystem services that support human civilizations, and that bats are at 506 THERYA Vol.6(3): 505-513 CARTA AL EDITOR risk for significant negative impacts by wind turbines, we must give serious attention to how we can design wind farms so as to minimize their negative environmental impacts. Here we discuss aspects of wind farm design that should be considered as routine procedures inherent in plans to establish a wind farm and to improve management of existing facilities. In doing this, serious attention needs to be directed to the unique nature of each potential site and its local bat fauna. We divide these considerations into biological and technological aspects. Of course, attention to bat mortality needs to be integrated with concerns for improving energy production efficiency and reducing bird fatalities as well (Hutchins 2014). Wind farms have been recorded to have a strong effect on mortality of birds (Erickson et al. 2014; American Wind Wildlife Institute 2015).