Providing evidence to improve practice

Individual study: Altering turbine speed reduces bat mortality at wind-energy facilities

Published source details

Arnett E.B., Huso M.M.P., Schirmacher M.R. & Hayes J.P. (2010) Altering turbine speed reduces bat mortality at wind-energy facilities. Frontiers in Ecology and the Environment, 9, 209-214


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Switch off turbines at low wind speeds to reduce bat fatalities Bat Conservation

In a replicated, randomized, controlled study in 2008 and 2009 in a forested area of Pennsylvania, USA (Arnett et al 2010) average nightly bat fatalities were reduced when the cut-in wind speed of turbines was increased. In 2008 and 2009, bat fatalities were significantly higher at fully operational turbines (both years average 2 bats/turbine/night) than curtailed turbines (0.3 and 0.7 bats/turbine over 25 nights at 5 m/s cut-in speed, 0.5 and 0.6 bats/turbine over 25 nights at 6.5 m/s cut-in speed). Each night from July to October in both years, twelve out of a total of 23 turbines were randomly assigned to one of three treatments: fully operational with a cut-in speed of 3.5 m/s, or curtailed with either a cut-in speed of 5 m/s or 6 m/s. There was no difference in the number of fatalities between the two curtailed turbine treatments. Daily carcass searches were conducted along transects in 120 x 126 m rectangular plots centred on each turbine, and fatality rates were corrected for searcher efficiency and scavenger removal. Six species were killed at the site with hoary bats Lasiurus cinereus, silver-haired bats Lasionycteris noctivagans and eastern red bats Lasiurus borealis being the most common. If applied to the entire wind farm, the operational changes made from July to October were projected to create an annual power output loss of 0.3% when cut-in speeds are increased to 5 m/s, and 1% when cut-in speeds are increased to 6 m/s.