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Bat Mortality and Wind Power: a problem of migration?
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In the push to develop new forms of sustainable energy, the wind power industry is at the forefront. Turbines that harness the power of wind already serve as effective power sources across the globe, and this proven effectiveness has led to vast increases in the number of turbines currently under construction. The general impact of wind turbines on the environment is likely far less than conventional power sources. However, recent evidence shows that certain species of bats are particularly susceptible to mortality from wind turbines. Bats are beneficial consumers of harmful insect pests, and migratory species of bats cross international and interstate boundaries.
Dead bats are turning up beneath wind turbines all over the world, but the mystery of why bats die at turbine sites remains unsolved. Is it a simple case of flying in the wrong place at the wrong time? Are bats attracted to the spinning turbine blades? Why do bats die at turbines in such large numbers? Although these questions remain unanswered, potential clues can be found in the patterns of mortality. Foremost, the majority of bats killed by wind turbines are species that migrate; in fact, peaks in mortality tend to coincide with periods of migratory activity. Bats probably follow corridors of high wind during migration, so the sites considered ideal for wind turbines, such as mountain ridges, could actually be places where bat populations funnel through while migrating.
Despite patterns indicating that bat mortality at turbines is somehow associated with migratory species, this phenomenon has not been investigated. At present, it is unclear whether bats killed by turbines are local residents, migrants moving through the area, or a combination of both. Further complicating matters is the fact that some of the species that die in smaller numbers at wind turbines are not known to migrate, although migratory habits of many bat populations are unknown and some of these may actually do so. Addressing these important topics is crucial to future efforts aimed at mitigating the impact of wind turbines on bat populations. In essence, does the problem center on migrating bats, or are migrating bats part of a larger problem? If it turns out that most of the bats killed by wind turbines are actively migrating, it will be easier to direct effective mitigation efforts, because the period of collisions will be shorter and the number of species involved more predictable. Because large numbers of individuals concentrate in small areas during migration, populations of migratory bats may be particularly susceptible to wind turbines, further emphasizing the need to determine their level of involvement.
The USGS is well-poised to answer questions regarding animal migration and the geographic origins of bats killed at wind power facilities. A cross-disciplinary (biology, geology, and geography) approach has put USGS scientists at the forefront of research into bat migration and distribution. For example, prior work by the USGS on the three bat species that die most frequently at wind turbine sites in North America has provided the most comprehensive picture, to date, of their migratory movements across the continent. These distributions have been mapped, as shown in the following links:
Seasonal distribution of hoary bats (Lasiurus cinereus) [.WMV format: 300KB]
Seasonal distribution of silver-haired bats (Lasionycteris noctivagans) [.WMV format: 300KB]
Seasonal distribution of red bats (Lasiurus borealis and L. blossevillii) [.WMV format: 300KB]
One research tool that is particularly well-suited to studying the origins of bats killed at wind turbines is stable isotope analysis. USGS scientists recently pioneered the application of stable hydrogen isotope analysis to the study of migration in terrestrial mammals and proved the efficacy of the technique for studying the continental movements of bats. Coincidentally, this groundbreaking research focused on the very same species of bat (the hoary bat, Lasiurus cinereus) that is killed most frequently at wind turbine sites across North America. Because of this, the USGS is in the unique position of having an existing framework of stable isotope data on which to build.
Continuing on this prior trajectory, USGS scientists are working to develop an active research program aimed at determining the geographic origins of bats killed by wind turbines across North America and to investigate other aspects of this phenomenon. Expertise and experience studying bat migration, combined with an existing infrastructure that promotes collaboration between disciplines, makes USGS well-equipped to effectively address the problem of bat mortality and wind power facilities. Only through further research will we make progress toward minimizing the impact of this new form of sustainable energy on our Nation’s wildlife.
To learn more about this work or opportunities to collaborate, contact
Paul Cryan
USGS Fort Collins Science Center
2150 Centre Ave., Bldg. C
Fort Collins, CO 80526-8118
Tel. 970.226.9389
Fax 970.226.9230
paul_cryan@usgs.gov
