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PIER Report: Golden Eagles and Wind Turbine Blade-Strike

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  • Bruce Mast
    CalBirders: A new report for the California Energy Commission s PIER program, Energy-Related Environmental Research Area, is now available online through links
    Message 1 of 1 , Nov 8, 2002

      A new report for the California Energy Commission's PIER program,
      Energy-Related Environmental Research Area, is now available online
      through links at the following location:


      The report is titled: "Golden Eagles In A Perilous Landscape: Predicting
      The Effects Of Mitigation For Wind Turbine Blade-Strike Mortality"

      For those who do not want to read the full report, here's the 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

      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.

      Bruce Mast
      Oakland, CA
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