Confirmation that eagle fatalities can be reduced by automated curtailment of wind turbines

1. Automated curtailment is potentially a powerful technique to reduce
collision mortality of wildlife with wind turbines. Previously, we used a
before-after-control-impact framework to demonstrate that eagle fatalities
declined after automated curtailment was implemented with the IdentiFlight
system at a wind power facility in Wyoming, USA. We received substantial
interest and feedback regarding our study and, here, we implement several
analytical suggestions and include more recent data that strengthen the
inference we draw from our results. 2. The five main analytical
suggestions we received were to 1) exclude from analysis data that were
collected during the period when automated curtailment was only partially
implemented; 2) only analyze data from a single make and model of turbine;
3) evaluate changes in the rate of fatality, instead of the yearly numbers
of fatalities that result from fluctuations around that rate; 4) calculate
the standard measure determining effects of a treatment in a
before-after-control-impact study; and, 5) examine yearly fluctuations of
the fatality rate during the before period. 3. After incorporating these
suggestions and including additional data collected since the prior paper
was published, our results confirm prior work. We demonstrate that eagle
fatalities were reduced by 85% (95% highest density interval = 12%, 100%)
after implementation of automated curtailment. Rate of fatalities declined
by 2.85 eagles per year (-0.67, 5.70) between before and after periods at
the treatment site and increased by 2.26 eagles per year (-7.37, 1.77) at
the control site. Overall, the fatality rate declined by 4.91 (-0.27,
11.27) more eagles per year at the treatment site than at the control
site. The probability that the fatality rate declined at the treatment
site relative to the control site was 0.97. 4. Our re-analysis strengthens
our inference by using more robust analyses and data to support the
conclusions of the prior study suggesting that automated curtailment was
effective at reducing eagle fatalities at our treatment site. Because of
the site- and species-specific nature of our work, future research should
examine the efficacy of automated curtailment at other sites, with other
species, and under different curtailment regimes.