Cooperative Fish and Wildlife Research Units Program: Massachusetts
Education, Research and Technical Assistance for Managing Our Natural Resources

Wind energy development is promoted by both government and nonprofit entities as an environmentally friendly alternative to greenhouse gas-emitting fossil fuels, but the technology can have negative impacts on wildlife, including bats (GAO 2005). Overall, a recent study estimated 600,000 bats were killed by wind power in the United States in 2012 (Hayes 2013). As wind power facilities expand and multiply, concern is growing that wind farm mortality could have significant effects on bat populations at large (Cryan 2011). The effects of wind development on bat populations may be especially detrimental to migratory tree and foliage-roosting bats, which comprise about 75% of all fatalities reported in North America (Arnett et al. 2008). In the northeastern United States, long-distance migrants include the hoary bat (Lasiurus cinereus), the eastern red bat (L. borealis), and the silver-haired bat (Lasionycteris noctivagans). These species face the greatest risks during their fall migration southward, with mortality at wind farms peaking during this season (Arnett et al. 2008). Little is known about the timing, routes, or drivers of migration in these species, or why they are particularly vulnerable to wind farm mortality during fall migration. Migratory activity in bats has been associated with nights of low wind speeds and the passage of storm fronts, as is the case for migrating songbirds (Arnett et al. 2008), but information about speed of migration, on a nightly and seasonal basis, stopover timing, and stopover location are lacking. Major bat migratory pathways in the northeastern U.S. have not been identified, but European bats follow linear features, including coastlines, when migrating (Serra-Cobo et al. 1998, Lesinski 2008, Ahlen et al. 2009, Furmankiewicz & Kucharska 2009) and songbirds often follow coastal routes during migration, so it has been hypothesized that North American bats may follow similar pathways (Cryan 2003, Johnson et al. 2011). Recent acoustic surveys in the Gulf of Maine have found activity of migratory bat species to be higher in coastal areas compared to inland sites (Stantec 2012), supporting the idea that coastal areas may serve as migratory pathways. In addition, there is a century-long historical record of migratory bat activity over the open ocean, sometimes at great distances from shore. Migratory bats utilize marine islands as stopover sites (Cryan & Brown 2007, Johnson et al. 2011), and have been observed visiting barren rocks 30 miles off the coast (Merriam 1897) and roosting on ships at sea (e.g. Nichols 1920, Thomas 1921, Griffin 1940, Corbet 1970). Acoustic surveys documented migratory bats flying over marine buoys on numerous occasions during the migration season (Stantec 2012). Taken together, these observations indicate that coastal and offshore areas, which face significant wind energy development in the near future, may serve as important habitat for migratory bats. Given the dearth of information about bat migration in general, and migration in coastal and offshore environments in particular, further research is needed in order to understand how best to site and operate coastal and offshore wind facilities to minimize bat mortality.