Reducing bat mortality at wind farms: testing a new method

A new study has found that letting wind turbines idle at low wind speed can reduce bat mortality from turbines substantially.

Wind turbines deadly to migratory bats…
Between 1997 and 2006, wind energy increased tenfold in installed capacity worldwide to meet a growing demand for clean energy. Unfortunately, some wind farms kill bats in large numbers, especially facilities with newer, taller turbines. In some areas bat fatalities outnumber bird kills by as much as 10 to 1. High rates of bat fatalities are particularly problematic because bats are long-lived animals that reproduce slowly making it more difficult for them to recover from population declines.

Eastern red bat (Lasiurus borealis) in glove.The majority of bats killed at wind farms are migratory tree bats including hoary bats (Lasiurus cinereus), eastern red bats (L. borealis), and silver-haired bats (Lasionycteris noctivagans) which migrate long distances often across multiple wind facilities. Past studies have found that bat fatalities are related to turbine height, geographic location and wind speed with more bats killed on low-wind nights. Given these findings, researchers from the University of Calgary and TransAlta Wind decided to test whether reducing the amount that turbine rotors turn during periods of low wind speed would decrease bat fatalities.

Testing new methods for reducing bat mortality…
The researchers conducted the experiment at a 2023-ha wind energy installation in southwestern Alberta from August 1, 2007 - September 1, 2007 (the period of the year with greatest bat fatalities). The facility made up of 39 Vestas V80 turbines has experienced a relatively high number of bat fatalities with approximately 1025 deaths recorded in 2006. The researchers altered operation of 21 randomly chosen turbines with the objective of leaving the turbines to be idle and motionless during low wind speeds. They utilized two different methods to modify the turbine motion during low winds: 1) They either changed the wind-speed trigger at which the turbine rotors were allowed to begin turning or 2) they altered blade angles to reduce rotor speed.

Findings and what they mean for bat conservation...
The study found that the two methods resulted in a 60 and 67.5% decrease in bat mortality respectively. They estimated that the 2nd method had no impact on electricity production and the 1st method had a reduction of approximately $200-$265 revenue (Canadian) per turbine during the month of the study (though they caution that costs could be higher or lower based on a variety of technical and market factors). This study offers promsing results for finding a method to reduce bat mortality from wind turbines. However, the researchers caution that more studies need to be conducted to test how effective and costly these methods are when used with other wind turbines, in different environmental settings, and with other bat species.

Source:	Journal of Wildlife Management
Title:	A Large-Scale Mitigation Experiment to Reduce Bat Fatalities at Wind Energy Facilities
Authors:	a) Erin Baerwald, b) Jason Edworthy, b) Matt Holder, and a) Robert Barclay
	a) University of Calgary; b) TransAlta Wind, Calgary