Resource Availability May Not Be a Useful Predictor of Migratory Bat Fatalities or Activity at Wind Turbines

Abstract

A better understanding of the ultimate mechanisms driving bat fatalities at wind turbines (i.e., the reason why bats are coming in close proximity to wind turbines) could inform more effective impact reduction strategies. One hypothesis is that bats come into close proximity to turbines due to existing resources (e.g., roosting sites) in the immediate area. Thus, if resource hotspots for bats could be identified in areas proposed for wind energy development, then fatalities could be reduced by siting turbines away from such hotspots. To explore this, we conducted a resource mapping exercise at a 48 km2 wind energy facility in north-central Texas. We mapped known resources (such as water sources, roosting sites, foraging sites, and commuting routes) for the 6 bat species present and compared resource availability with observed fatalities and acoustic activity. Although resource mapping identified concentrations of known resources for all species, it did not predict bat activity or fatalities. For example, Lasiurus cinereus and Lasiurus borealis comprised >90% of the fatalities, yet we found no positive relationship between resource availability and fatalities or acoustic activity for either species. Furthermore, up to 33% of these fatalities occurred at turbines without known resources within 200 m of the turbines, demonstrating that the fine-scale distribution of resources may not effectively inform turbine siting for these two migratory species. The challenge, therefore, remains to determine why bats during the migratory season are coming in close proximity with wind turbines.