Washington is experiencing rapid changes in the landscape in areas where relatively constant, high-velocity winds provide the opportunity to capture wind energy through construction of wind turbines. Many of these areas, particularly in shrub-steppe regions, were formerly unsuitable for other types of land use because of remoteness or topography. For the same reasons, many of these areas provide high quality wildlife habitats including raptor migration paths, nesting areas, and wintering habitats. Technology has improved wind turbine design and placement since the 1980s when studies led by Grainger Hunt identified turbine fatalities as a serious population threat to golden eagles and other raptors near Altamont Pass, California. However, wind turbines continue to be a unique disturbance and potential source of mortality to birds and bats because turbine blades extend into flight zones, the “bread and butter” niche these animals occupy during daily hunting, movements, and migration. Rotating turbine blades constantly change orientation and speed depending on wind conditions, further increasing potential hazards. Infrastructure associated with turbines including roads and powerlines may also affect avian behavior directly because of disturbance or indirectly due to habitat loss.
The most concentrated area of wind energy development in Washington is along the Columbia Gorge. This area is used by migrant and wintering raptors and a diverse nesting population including red-tailed hawks, Swainson’s hawks, golden eagles, and ferruginous hawks. Implications of turbines within home ranges of these nesting raptors raise several questions: 1) Do these birds change their home range use after turbines are built? 2) Do they, or their young, experience fatal collisions with the turbines? If so, can fatality be explained as a function of the distance of the turbines to the nest and what part do flight skill and chance play in turbine avoidance? 3) What is the long-term viability and population contribution of raptor nest territories within wind power development zones? Ultimately, the answers to these questions will help us better recommend nest buffer distances before turbine construction, and assess population impacts of expansive turbine development even on the more common raptor species.
We began seeking answers to these questions in 2007 when we initiated a study in the Columbia Gorge where several wind projects were in various stages of construction. Our objectives were to: 1) test the utility of GPS telemetry in monitoring the movements and survival of adult raptors before and after turbine construction involving several wind projects; 2) quantify range use associated with existing turbines, and monitor survival and monitor nest activity and productivity of these birds; and 3) for raptors captured prior to turbine construction, evaluate pre-and post construction range use.
As of 2009, three golden eagles, nine red-tailed hawks, and six Swainson’s hawks have been captured in the study. Four of these hawks are being monitored outside of the project area associated with other wind projects.
Fifteen of the eighteen monitored raptors occupied territories. Eight resident birds were captured prior to turbine construction, but only three of these birds have been monitored post-construction as a result of mortality (2), unknown loss of PTT signal (1), and delayed construction (2). The remaining eight birds have been monitored after turbine construction.
None of the telemetered raptors were known to have died in turbine collisions, although at least 4 red-tailed hawks, a golden eagle, and a prairie falcon were confirmed fatalities near turbines associated with these wind projects since the beginning of 2009. Eight PTTs remain active at the beginning of 2010.
We are presently analyzing movement and altitude data from this work. In spring, 2010, the study will change focus to examine ferruginous hawk range use associated with wind turbines on the Washington and Oregon sides of the Columbia River in a study funded by WDFW and the Oregon Department of Fish and Wildlife. We have captured and monitored three adult ferruginous hawks as part of the pilot work for this study. The effort is half of a study part of a larger cooperative effort with the wind industry, agency, and non-governmental organizations to address concerns related to adult and juvenile ferruginous hawk ecology in wind power project areas.