Still Hanging On: The Endangered Indiana Bat

Jeff Hyman, Bill Weeks, and CLC are embarking on our second year arguing tor sufficient protection of the Endangered Indiana Bat from Wind Turbines. This article sums up our research and describes a possible solution to reduce the impact of increased wind energy on the Indiana Bat and other bat and bird species.


The Indiana Bat is one of two federally endangered native bat species in Indiana. Primarily found in the Midwest and Southern regions of the U.S., the Indiana Bat spends the winter months (roughly October-April) hibernating in caves and abandoned mines. Bats are communal species, and one death can greatly affect a population. To protect the Indiana Bat from extinction, the Conservation Law Center is interested in reducing the threat of wind turbines to the endangered species.

Summer roosts vary greatly within the Indiana Bat species. Typically, they roost under the exfoliating bark of dead and living trees and in tree cavities within both forests and residential neighborhoods. Indiana Bats spend the summer months eating insects within five miles of their roosts. Maternity colonies roost separately from the rest of the colony, and pups are born between late June and early July. The baby bats are already capable of flight by early August in time for migration.

Come August, members of the colony begin migration across the Midwest. During this time, the wind turbine threat is at its peak. The Indiana Bat does not travel as far as many migratory birds between summer and winter roosts. Its migratory journey varies up to the distance between Cleveland, OH and Louisville, KY (about 350 miles). Across the Midwest, wind farms interrupt this migratory route, and an estimate of over 1 million bats, across species, annually fall victim to the blade. Two possible fatal impacts may occur when a bat flies into a turbine; the sudden drop in air pressure near the blade causes a hemorrhaging of the lungs, or the high speed of the blade kills the bat on impact. 

Production of wind energy in the U.S. is expected to rise 500% by 2030. This could lead to close to 20 million bat fatalities if we do not adopt protective measures. According to a study conducted by Bat Conservation International in 2008 and 2009, adjusting wind turbine cut-in speed would reduce the number of bat fatalities significantly. Cut-in speed is the wind speed at which turbine operation is allowed to begin. The study shows "a 44%–93% reduction in fatalities with only a 0.3%–1% annual loss of energy production” (see diagram). Bats prefer not to fly in high winds. By keeping turbines dormant until the higher speed (14.5 miles per hour), a significant majority of animals are free from the fatal harm described above. 

By Keeping turbines dormant until the higher speed, a significant majority of animals are free from fatal harm.

Renewable energy is an important societal objective; however, it is also important to keep in mind that wind farms kill many species of bats and birds. The Conservation Law Center is arguing that companies must minimize bat deaths to the maximum extent practicable. If the cost of increasing the cut-in speed of a turbine is less than 1% of the annual energy production of a farm and prevents more than half the potential the potential fatalities of bats, how does that compare to the cost of a loss of species within an ecosystem? The answer to that question will determine whether the next decades will bring us the benefits of biodiversity or the permanent loss of the Indiana Bat.


Arnett, Edward B., Manuela Mp Huso, Michael R. Schirmacher, and John P. Hayes. "Altering Turbine Speed Reduces Bat Mortality at Wind-energy Facilities." Frontiers in Ecology and the Environment 9.4 (2011): 209-14. Web.

"Wind Energy." Wind Energy. Bat Conservation International, n.d. Web. 28 Oct. 2015.

"Indiana Bat (Myotis Sodalis)." USFWS Midwest Endangered Species, 8 Aug. 2015. Web. 28 Oct. 2015.