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Home range and resource selection by GPS-monitored adult golden eagles in the Columbia Plateau Ecoregion: Implications for wind power development

Authors


  • Associate Editor: Marc Bechard.

ABSTRACT

Recent national interest in golden eagle (Aquila chrysaetos) conservation and wind energy development prompted us to investigate golden eagle home range and resource use in the Columbia Plateau Ecoregion (CPE) in Washington and Oregon. From 2004 to 2013, we deployed satellite transmitters on adult eagles (n = 17) and monitored their movements for up to 7 years. We used the Brownian bridge movement model (BBMM) to estimate range characteristics from global position system (GPS) fixes and flight paths of 10 eagles, and modeled resource selection probability functions (RSPFs). Multi-year home ranges of resident eagles were large (99% volume contour; math formula, SD = 370.2 km2) but were one-third the size (math formula, SD = 94.6 km2) and contained half as many contours when defined by 95% isopleths. Annual ranges accounted for 66% of multi-year range size. During the breeding season (16 Jan–15 Aug), eagles occupied ranges that were less fragmented, about half as large, and largely contained within ranges they used outside the breeding season (math formula overlap = 82.5%, SD = 19.0). Eagles selected upper slopes, rugged terrain, and ridge tops that appear to reflect underlying influences of prey, deflective wind currents, and proximity to nests. Fix distribution predicted by our resource selection model and that of 4 eagles monitored independently in the CPE were highly correlated (rs = 0.992). Our findings suggest conservative landscape management strategies addressing development in lower-elevation montane and shrub-steppe/grassland ecosystems can best define golden eagle ranges using exclusive 12.8-km buffers around nests. Less conservative strategies based on 9.6-km buffers must include identification and management of upper slopes, ridge-tops, and areas of varied terrain defined by predictive models or GPS telemetry. For both strategies, high, year-round intensity of eagle flight and perch use within 50% volume contours (average 3.2 km from nests) due to nest centricity may dramatically increase the probability of eagle conflict with wind turbines in core areas as evidenced by eagle turbine strikes that studies have documented within and beyond this zone. © 2014 The Wildlife Society.

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