Where Eagles Nest, the Wind also Blows: Consolidating Habitat and Energy Needs

December 17, 2012

As the United States seeks to develop domestic energy, renewable energy sources, such as wind and solar, have become increasingly attractive options. However, like any other human activity, these alternative sources can have unintended consequences for wildlife. Wind turbines are a particular issue for birds.

Across the more remote shrublands and grasslands of the western United States, raptor species such as golden eagles, ferruginous hawks, and prairie falcons need large, undisturbed areas to nest, hunt, and raise their young. These wide-open spaces also tend to possess considerable potential for wind energy development. In the case of raptors, sensitivity to human disturbance can discourage nesting at a location. Wind turbines, 150 feet tall with large spinning blades, can intrude upon the otherwise uninterrupted airspace, and collisions mean certain mortality to many avian species. The challenge for managers lies in conserving the critical landscapes that wildlife populations depend on as energy development expands.

Habitat maps displaying relative quality of habitat for golden eagle nest sites. Statistical multi-scale habitat models were applied in a GIS to make resource selection predictions, at 30-m resolution, across major ecoregions in Wyoming, the Wyoming Basin, and the Northwest Great Plains. USGS image.

Map showing wind power classes (source: National Renewable Energy Laboratory) for 50 meters above-ground elevation in Wyoming. USGS image.

Map of transects flown since 2006 in search of golden eagles. The U.S. Fish and Wildlife Service uses the late-summer data to estimate population size of golden eagles. FORT scientists are using these data to identify critical habitat relationships that underlie population dynamics. Note: Curvature at outer edges is caused by map projection distortion. USGS image.

Golden eagle family on nest in Medicine Bow National Forest, Wyoming. U.S. Forest Service photo.

Golden eagle on snow. Photo by David Menke, U.S. Fish and Wildlife Service.

Using Prediction to Plan for Prevention

As energy development escalates in Wyoming, the risks posed to raptor populations are of increasing concern to the U.S. Fish and Wildlife Service. In support of a Federal mandate to protect trust species (including raptors) and the wind energy industry’s need to find suitable sites on which to build wind farms, scientists at the USGS Fort Collins Science Center (FORT) and their partners are conducting research to help reduce impacts to raptor species from wind energy operations. Potential impacts include collision with the turbine blades as well as habitat disruption and disturbance from construction and operations. To potentially avoid or reduce such impacts, FORT is developing a science-based tool that will provide industry and resource managers with the biological basis for sustainably siting wind turbines and also conserving important habitats.

Standard mitigation measures following development activities, such as seasonal distance restrictions of activities relative to known roost or nest sites, may not be sufficient to meet the complex habitat requirements of wide-ranging raptors. Typically, mitigation actions are only applied during one season, focus only on known nest or roost sites, and do not consider other habitats such as foraging areas and movement corridors. Furthermore, mitigation following development may be ineffective since the disturbance on the ground has already taken place.  Identification of priority habitats for raptors in Wyoming can help address these limitations. First, habitat selection models based on existing raptor and habitat data can predict habitat quality in areas not previously surveyed. Second, habitat-selection modeling can also predict the location of lower-quality habitats, where wind energy development might have less impact on these birds.

To this end, FORT scientists are developing a quantitative predictive model of the relationship between available habitat and habitat use for three raptor species in Wyoming: golden eagle, ferruginous hawk, and prairie falcon. Because of the availability of comprehensive data on nesting sites, golden eagles in Wyoming are the prototype species (and location) for the first phase of this investigation.

A “SWOT” for Golden Eagles

The golden eagle study uses publicly available data to identify the relative quality of habitat for golden eagle nesting across Wyoming. Using statistical models, scientists estimated the influence of environmental and anthropogenic features on golden eagle nest-site selection from local to landscape scales. Researchers mapped results in a Geographic Information System (GIS) to display continuous surfaces proportional to probability of use by golden eagles. Overlaying habitat and wind potential maps generated by the National Renewable Energy Laboratory, scientists then identified potential conservation areas as well as areas where eagles are most at risk if wind energy is developed. Using these maps, scientists applied a framework similar to a “SWOT” analysis (Strengths, Weakness, Opportunities, and Threats) sometimes conducted for business development. In the case of golden eagle habitat, the analysis highlighted “strengths” and “weaknesses” (high- and low-quality habitat) across the landscape, explicitly identifying “opportunities” for targeted conservation efforts (high-quality habitat, low energy potential), and “threats” (high-quality habitat, high energy potential). These analyses will help guide resource managers and the wind energy industry concerning the strategic siting of wind energy facilities and identification of high-value areas for conservation.

Other Raptors in the Lineup

FORT scientists and their partners are concurrently building similar products to help quantify habitat needs for several additional raptor species in Wyoming. These products will become available during 2012 and 2013 and include:

• dynamic models for golden eagle occupancy across 14 western states to predict how occupancy patterns are influenced by habitat over time;
• habitat-based models predicting potential suitable nesting sites in Wyoming for ferruginous hawks and prairie falcons; and
• population trend estimates to determine whether raptor populations cycle, and if so, quantify the periodicity and direction of such cycling using data from the North American Breeding Bird Survey.

Research and modeling results will generate information that can inform decisions about how to design, site, and manage wind farms in ways that minimize effects on golden eagles during a critical life-stage. Results also will support the U.S. Fish and Wildlife Service in effective eagle conservation by facilitating the prioritization of locations for strategic and/or focused conservation efforts. Ultimately, investigators anticipate that these models can be applied to other raptor species in landscapes for which nesting data exists.

For More Information

Jason Tack
USGS Fort Collins Science Center
2150 Centre Ave., Bldg. C
Fort Collins, CO 80526
Phone: 970-226-9138
Email: jtack@usgs.gov

Also @ FORT

• Energy, Land Use, and Sagebrush Ecosystems: Finding the Delicate Balance
• Habitat Prioritization for Selected Raptor Species in Wyoming
• Interactive Energy Atlas for Colorado and New Mexico: An Online Resource for Decisionmakers and the Public
• Locations and attributes of wind turbines in Colorado, 2009
• Locations and attributes of wind turbines in New Mexico, 2009
• Resources for Understanding the Effects of Wind Energy Development
• Spatial mapping and attribution of Wyoming wind turbines