Altering turbine speed reduces bat mortality at wind‐energy facilities

Wind‐turbine operations are associated with bat mortality worldwide; minimizing these fatalities is critically important to both bat conservation and public acceptance of wind‐energy development. We tested the effectiveness of raising wind‐turbine cut‐in speed – defined as the lowest wind speed at which turbines generate power to the utility system, thereby reducing turbine operation during periods of low wind speeds – to decrease bat mortality at the Casselman Wind Project in Somerset County, Pennsylvania, over a 2‐year period. Observed bat mortality at fully operational turbines was, on average, 5.4 and 3.6 times greater than mortality associated with curtailed (ie non‐operating) turbines in 2008 and 2009, respectively. Relatively small changes to wind‐turbine operation resulted in nightly reductions in bat mortality, ranging from 44% to 93%, with marginal annual power loss (≤ 1% of total annual output). Our findings suggest that increasing turbine cut‐in speeds at wind facilities in areas of conservation concern during times when active bats may be at particular risk from turbines could mitigate this detrimental aspect of wind‐energy generation.