Long-term fatality monitoring revealed multi-annual cycles of fatalities in the Altamont Pass Wind Resource Area (APWRA), California. Cycle periods were 4-5 years, with peaks recorded in 2000, 2006-2007 and 2010-2011 (a peak year might have been missed between 2003 and 2005, when no monitoring was performed). Nadir years were in 2002 and 2009. Fatality rates during the latest peak years were damped compared to previous peaks among most of the old-generation turbines. The damping of the most recent fatality peaks was likely due to the removals of wind turbines that the Alameda County Scientific Review Committee (SRC) rated 8.5-10 for collision hazard. An exception to this damping was at the 95 KW Vestas turbines in the Santa Clara project, where Alameda County exempted the project from hazardous turbine removals. At Santa Clara, the 2011 fatality peaks were higher than the previously recorded fatality peaks.
Wind turbines the SRC rated 8-10 for collision hazard yielded disproportionately high numbers of golden eagle, red-tailed hawk and American kestrel fatalities prior to 2009, but killed disproportionately fewer numbers of these species after most of the turbines rated 8.5-10 were removed. However, even though the turbine removals were highly effective, the removals happened towards the end of the declining portions of fatality cycles. Raptor fatalities at Diablo Winds declined 46% from 2006 through 2010, but this reduction had nothing to do with the Avian Protection Program because no fatality reduction measures were implemented at Diablo Winds. On the other hand, raptor fatalities at Diablo Winds were lower on average than they were during the years of the FloWind project prior to repowering. Given the complexity of the fatality patterns in the APWRA due to multi-annual cycles of fatalities, interpreting the effects of management actions can by prone to confounding. This complexity coupled with the large standard errors associated with the fatality rate estimates and changes in the extent of monitoring undermines the credibility of the recent conclusion that a 50% fatality reduction was achieved by the Avian Protection Program. Determining the level of change in fatality rates needs to be attempted within the context of a multi-annual cycle. An example would be comparing fatality rates between peaks of the cycle.
The SRC’s recommended management actions were sound, as the hazardous turbine ratings were effective. In the near term, turbine removals should be expanded to those rated 8, consistent with the SRC’s standing recommendation. The turbines rated 7 and 7.5 should be repaired or removed to lower their ratings to <7. Wind turbines hazardous to burrowing owls need to be identified and relocated or removed. More important than these management actions, the old generation turbines should be repowered as soon as possible and the new turbines should be carefully sited to minimize collision risk. Repowering remains the quickest and most likely way to achieve the 50% reduction target set by the Settling Parties in January 2007.