Wind Turbines as Landscape Impediments to the Migratory Connectivity of Bats
Cryan, Paul M., Environmental Law
I. INTRODUCTION II. THE UNIQUE AND MYSTERIOUS MIGRATIONS OF BATS A. Winter Survival Strategies B. The Elusive Bat: Research Challenges C. Unique Migration Behaviors of Bats III. PERILS OF MIGRATION IN BATS A. Species Characteristics Indicate Higher Natural Mortality in Migratory Bats B. Migratory Bat Collisions with Human-Made Structures IV. WIND TURBINES: AN EMERGING THREAT TO BAT MIGRATIONS A. Documenting Bat Fatalities at Wind Energy Sites B. Emerging Patterns of Bat Mortality at Wind Energy Sites C. Impacts on Migratory Bat Populations V. THE IMPORTANCE OF SCIENTIFIC RESEARCH INTO BAT MORTALITY AT TURBINES A. Gaps in Legal Protection B. Gaps in Monitoring and Conservation at Wind Energy Sites .. C. Benefits of Research on Bat Mortality at Wind Turbines ... VI. CONCLUSION
Several species of insectivorous bats migrate hundreds to thousands of kilometers each spring and autumn, crossing a wide variety of landscape features and ecosystems on their journey. (1) These long-distance nocturnal flights, combined with the cryptic diurnal habits of migratory bats, have made it extremely difficult to uncover the details of their seasonal whereabouts, movements, and migration behaviors. Beginning around the turn of the millennium, a scatter of reports came to light regarding the surprising numbers of migratory bats found dead beneath wind turbines during autumn across both North America and Europe. (2) Since the release of these studies, mortality of migratory bats at wind turbines during late-summer and autumn has become a major conservation issue. (3) Whereas there were no known energy-related imminent threats to populations of migratory bats prior to about the year 2000, observed fatality rates of certain species at turbines now indicate the distinct possibility of population declines. At some sites, the estimated number of bats killed range from hundreds to over one thousand in a single autumn migration season, with cumulative estimates for North America ranging into the hundreds of thousands per year, eclipsing any previously observed mortality of these mysterious migrants. (4) Over the past decade it has become apparent that wind turbines have the potential to seriously impede and disrupt the migration--and therefore long-term persistence--of several species of bats at a continental scale. Importantly, none of the migratory bats most affected by wind turbines are protected by national conservation laws or international treaties, (5) so legal mandates for researching and finding practical solutions to the problem are lacking.
This Article describes the unprecedented bat mortality caused by wind turbines, and the potentially disastrous effects on certain bat populations. Current laws may be insufficient to protect bat migrations, and additional research is needed to identify effective conservation solutions. Part II includes an overview of migration in bats and emphasizes how little we know about this phenomenon. Part III discusses the inherent risks of migration in bats, including both natural and human-caused mortality. Part IV provides background on the emerging problem of bat fatalities at wind turbines and compares turbine-induced mortality to other known sources of mortality in migrating bats. Part V highlights the importance of scientific research in understanding the scope and magnitude of bat mortality at turbines, and in developing effective solutions to the problem. The Article concludes by identifying the challenges associated with developing research and conservation strategies aimed at poorly understood migratory species that are not protected by law.
H. THE UNIQUE AND MYSTERIOUS MIGRATIONS OF BATS
There are approximately 5400 species of mammals on Earth, of which about 1100 are bats. (6) Bats occur nearly everywhere but Antarctica and some remote islands, playing important functional roles in the majority of our planet's terrestrial ecosystems. …