Assessing regional sources of bat mortality at wind turbine sites using stable isotopes and population genetics

Background/Question/Methods

Government initiatives designed to address global climate change have spurred the proliferation of wind energy projects in the United States and abroad. Although wind energy development represents a move toward reducing greenhouse gas emissions, an unanticipated impact has been widespread mortality of migratory tree bats. To address the extent to which bat populations are affected by losses caused by wind turbines in the eastern U.S., fur and wing tissue samples were collected from hoary bats (Lasiurus cinereus) and eastern red bats (L. borealis) killed at 18 wind energy facilities in the central Appalachian Mountains (WV, MD, and PA) during 5 years (2003, 2009–2012). Stable hydrogen isotopes (δD) of fur were used to develop likelihood-of-origins maps for each bat and thus determine whether fatalities were comprised of individuals summering locally and/or non-local individuals killed during migration. Habitat suitability modeling and historic occurrence records were used to further constrain geographic assignments. DNA isolated from wing tissue was analyzed using 14 microsatellite markers and sequence data from the mitochondrial cytochrome b gene to determine the effective population sizes and genetic structure of bat populations and to test for the presence of recent genetic bottlenecks.

Results/Conclusions

δD values for 249 hoary bats range between -124.2 and -22.9‰, which suggests a broad summering distribution from mid-Saskatchewan eastward to Maine and southward to the southern Appalachian Mountains. Conversely, δD values for 144 eastern red bats range between -39.7 and 23.0‰, which is indicative of a more restricted summering distribution along coastal regions of the mid-Atlantic and slightly north of the central Appalachian Mountains. Population genetic data indicate large effective population sizes, high diversity, and little to no population structuring in hoary bats, consistent with a broad summering distribution as inferred by δD and previous studies of migratory pathways. Similar genetic analysis with eastern red bats suggests a structured population with 2 subpopulations and lower average genetic diversity, consistent with a more restricted summering distribution and known life history characteristics. Collectively, these results imply that eastern red bats may be more heavily impacted by wind energy development in the central Appalachians than hoary bats because the former species has a more restricted summering distribution and structured population than the latter. Given the projected proliferation of wind energy facilities, future research efforts should focus on assessing the potential for (sub)population declines.