Raptor Interactions with Wind Energy: Case Studies from Around the World

The global potential for wind power generation is vast, and the number of installations is increasing rapidly. We review case studies from around the world of the effects on raptors of wind-energy development. Collision mortality, displacement, and habitat loss have the potential to cause population-level effects, especially for species that are rare or endangered. The impact on raptors has much to do with their behavior, so careful siting of wind-energy developments to avoid areas suited to raptor breeding, foraging, or migration would reduce these effects. At established wind farms that already conflict with raptors, reduction of fatalities may be feasible by curtailment of turbines as raptors approach, and offset through mitigation of other human causes of mortality such as electrocution and poisoning, provided the relative effects can be quantified. Measurement of raptor mortality at wind farms is the subject of intense effort and study, especially where mitigation is required by law, with novel statistical approaches recently made available to improve the notoriously difficult-to-estimate mortality rates of rare and hard-to-detect species. Global standards for wind farm placement, monitoring, and effects mitigation would be a valuable contribution to raptor conservation worldwide.publishedVersio

Increased flight altitudes among migrating golden eagles suggest turbine avoidance at a Rocky Mountain wind installation.

Potential wind-energy development in the eastern Rocky Mountain foothills of British Columbia, Canada, raises concerns due to its overlap with a golden eagle (Aquila chrysaetos) migration corridor. The Dokie 1 Wind Energy Project is the first development in this area and stands as a model for other projects in the area because of regional consistency in topographic orientation and weather patterns. We visually tracked golden eagles over three fall migration seasons (2009-2011), one pre- and two post-construction, to document eagle flight behaviour in relation to a ridge-top wind energy development. We estimated three-dimensional positions of eagles in space as they migrated through our study site. Flight tracks were then incorporated into GIS to ascertain flight altitudes for eagles that flew over the ridge-top area (or turbine string). Individual flight paths were designated to a category of collision-risk based on flight altitude (e.g. flights within rotor-swept height; ≤150 m above ground) and wind speed (winds sufficient for the spinning of turbines; >6.8 km/h at ground level). Eagles were less likely to fly over the ridge-top area within rotor-swept height (risk zone) as wind speed increased, but were more likely to make such crosses under headwinds and tailwinds compared to western crosswinds. Most importantly, we observed a smaller proportion of flights within the risk zone at wind speeds sufficient for the spinning of turbines (higher-risk flights) during post-construction compared to pre-construction, suggesting that eagles showed detection and avoidance of turbines during migration

Proportion of risk zone and higher-risk crosses under tailwinds.

<p>Proportion of golden eagle ridge-top crosses within risk zone (≤150 m above ground) and of higher-risk (within risk zone at winds above turbine cut-in speed 6.8 km/h) under tailwind conditions during pre- and post-construction. Values above bars represent sample size.</p

Proportion of golden eagle risk zone and higher-risk crosses.

<p>Proportion of golden eagles observed in the study area that flew over the ridge-top area (100 m buffer around proposed turbine string), at heights considered to be within the turbine risk zone (≤150 m above ground), or made a higher-risk flight into the risk zone (risk zone crosses that occurred at winds above turbine cut-in speed [6.8 km/h]) during pre-construction versus post-construction years. Values above bars represent sample size.</p

Golden eagle altitude (m above ground) over ridge top by wind speed (km/h).

<p>Golden eagle flight altitude above the ridge-top area (m above ground) versus ground-based wind speed (km/h) during pre- (<i>n</i> = 60) and post-construction (<i>n</i> = 148) years. Some data points overlap. Grey box represents higher-risk flight zone (risk zone [≤150 m above ground] and above turbine cut-in speed [6.8 km/h]).</p

Proportion of risk zone and higher-risk crosses under headwinds.

<p>Proportion of golden eagle ridge-top crosses within risk zone (≤150 m above ground) and of higher-risk (within risk zone at winds above turbine cut-in speed 6.8 km/h) under headwind conditions during pre- and post-construction. Values above bars represent sample size.</p

Study site.

<p>Site map of the Dokie 1 Wind Energy Project in the Peace River Regional District of northeast British Columbia, Canada (55°46′ 28″ N, 122°16′ 49″ W).</p

Golden eagle flight altitude (m above ground) above ridge top.

<p>Golden eagle flight altitudes above the ridge-top area during fall migration over one pre-construction (<i>n</i> = 60) and two post-construction (<i>n</i> = 148) seasons. Box represents median, first and third quartiles, and whiskers the maximum and minimum altitudes. Dashed line represents risk zone (≤150 m above ground).</p

Summary of logistic regression examining the association of temporal and environmental variables on the likelihood of flying over the ridge-top area (100 m buffer around proposed turbine string) at rotor swept height (risk zone; ≤150 m above ground) at the Dokie 1 Wind Energy Project between 30 September–24 October, 2009–2011.

<p>The response measure under consideration was whether eagles flew within the risk zone (1) or not (0).</p

Percent of all golden eagles observed in the study site (within 2 km from turbine string) that were: over the ridge-top area (within 100 m from turbine string); within the risk zone (≤150 m above ground); and, within the risk zone at winds above turbine cut-in speed (higher-risk flight; 6.8 km/h) at the Dokie 1 Wind Energy Project site between 30 September–24 October in pre- (2009) and post-construction (2010–2011) years.

<p>Percent of all golden eagles observed in the study site (within 2 km from turbine string) that were: over the ridge-top area (within 100 m from turbine string); within the risk zone (≤150 m above ground); and, within the risk zone at winds above turbine cut-in speed (higher-risk flight; 6.8 km/h) at the Dokie 1 Wind Energy Project site between 30 September–24 October in pre- (2009) and post-construction (2010–2011) years.</p