Golden Eagles in a Perilous Landscape: Predicting the Effects of Mitigation for Wind Turbine Blade-Strike - Consultant Report

Publication Number:    P500-02-043F

Abstract:
The Predatory Bird Research Group, University of California, Santa Cruz, has been conducting a long-term field investigation of the ecology of golden eagles (Aquila chrysaetos) in the vicinity of the Altamont Pass Wind Resource Area (WRA) where turbine blade strikes kill an estimated 40-60 eagles per year. Our seven-year study was based on the aerial tracking of 257 radio-tagged eagles and an annual nesting survey of 60-70 pairs within about 30-km of the WRA. Of 100 deaths recorded among the tagged eagles, 42 were attributed to wind turbines, although the actual number was higher because the blades occasionally destroyed the transmitter. Comparisons of eagle location data with the distribution of blade-strike fatalities in the WRA showed that conditions within areas containing Type-13 turbines (the Kenetech 56-100 on an 18.3-meter lattice tower) were more dangerous to eagles than those in areas containing other types of turbines. It is unknown whether this lethality arose from the Type-13 configuration itself or from other factors such as spacing between turbines or extraneous environmental influences. Type-13s are set closer together than other turbines in the WRA, and eagles may have particular difficulty passing between (or under) them, especially in conditions of high winds and turbulence. California ground squirrels were the principal prey of golden eagles in the WRA, and eagles were attracted to areas of high squirrel concentration. Reduction of ground squirrel numbers around the wind turbines would reduce the incidence of blade strike deaths. Squirrel control would impact other wildlife in the WRA, but could be partially mitigated by off-site conservation easements. A demographic analysis produced a point estimate of no annual change in population size, but the variance fell equally into the alternatives of increase and decrease. If the point estimate of the model is correct, the population is failing to maintain a contingent of nonbreeding adults (floaters) which buffer the breeding sector in healthy populations. However, throughout the study, virtually all nesting territories occupied by adult pairs in one year were reoccupied the next, suggesting either a demographic balance in the local population or buffering by immigrant floaters.

Author(s):  Grainger Hunt

Commission Division:    Technology Systems Division - R&D, PIER (500)

Office/Program:    PIER: Public Interest Energy Research

PIER Program Area:    Avian-Energy Mitigation Program

Date Published:    2002

Date On Line:    07/02/2004

Acrobat PDF File Size: 72 pages, 2,000 kilobytes**