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 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

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

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

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

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

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

K (2013) Flight paths of migrating golden eagles and the risk associated with wind energy development in the Rocky Mountains. Avian Conservation and Ecology 8: 12

ABSTRACT. In recent years, the eastern foothills of the Rocky Mountains in northeastern British Columbia have received interest as a site of industrial wind energy development but, simultaneously, have been the subject of concern about wind development coinciding with a known migratory corridor of Golden Eagles (Aquila chrysaetos). We tracked and quantified eagle flights that crossed or followed ridgelines slated for one such wind development. We found that hourly passage rates during fall migration peaked at midday and increased by 17% with each 1 km/h increase in wind speed and by 11% with each 1°C increase in temperature. The propensity to cross the ridge tops where turbines would be situated differed between age classes, with juvenile eagles almost twice as likely to traverse the ridge-top area as adults or subadults. During fall migration, Golden Eagles were more likely to cross ridges at turbine heights (risk zone, &lt; 150 m above ground) under headwinds or tailwinds, but this likelihood decreased with increasing temperature. Conversely, during spring migration, eagles were more likely to move within the ridge-top area under eastern crosswinds. Identifying Golden Eagle flight routes and altitudes with respect to major weather systems and local topography in the Rockies may help identify scenarios in which the potential for collisions is greatest at this and other installations. RÉSUMÉ. Récemment, les contreforts des Rocheuses dans le nord-est de la Colombie-Britannique ont attiré l&apos;attention comme site potentiel d&apos;un développement éolien industriel, tout en faisant simultanément l&apos;objet de préoccupations puisque ce projet coïnciderait avec un corridor de migration connu d&apos;Aigles royaux (Aquila chrysaetos). Nous avons suivi et quantifié les vols d&apos;aigles qui ont traversé ou longé les lignes de crêtes visées par un projet éolien de ce genre. Nous avons constaté que le taux de passage horaire durant la migration automnale atteignait un maximum à midi et augmentait de 17 % pour chaque km/h d&apos;augmentation de la vitesse du vent, et de 11 % pour chaque °C d&apos;augmentation de la température. La propension à traverser les sommets des crêtes où seraient installées les éoliennes différait selon les classes d&apos;âge, les jeunes aigles de l&apos;année ayant deux fois plus de chance de le faire que les adultes ou les jeunes plus âgés. Durant la migration automnale, les aigles traversaient davantage les crêtes à hauteur d&apos;éoliennes (zone de risque, &lt; 150 m au-dessus du niveau du sol) sous un vent de face ou arrière, mais cette tendance diminuait avec l&apos;augmentation de la température. En revanche, durant la migration printanière, les aigles étaient plus susceptibles de survoler la région des sommets sous un vent latéral de l&apos;est. La détermination des trajectoires et des altitudes de vol des Aigles royaux, selon les systèmes météorologiques prédominants et la topographie locale des Rocheuses, peut contribuer à identifier les scénarios dans lesquels les risques de collision sont les plus élevés, que ce soit pour ce projet éolien ou d&apos;autres