A Spatially Explicit Model to Predict the Relative Risk of Golden Eagle Electrocutions in the Northwestern Plains, USA

Electrocution of Golden Eagles (Aquila chrysaetos) on overhead power poles is a conservation concern in the western United States. The US Fish and Wildlife Service recommends retrofitting power poles to minimize electrocution risk as one mechanism for compensatory mitigation to offset permitted take for Golden Eagles. Because densities of Golden Eagles and power poles vary spatially, identifying where poles should be retrofitted to best meet compensatory mitigation goals is of conservation importance. We developed a model that predicts relative risk of eagle electrocution based on the overlap between spatial models of Golden Eagle nest-site density and power pole density within the Northwestern Plains ecoregion. Risk was unevenly distributed: areas with the highest electrocution risk were rare (1.1% by area), while lowest risk areas were common (53.6% by area). We tested model predictions with independent data consisting of locations of Golden Eagle electrocution mortalities (n = 342). Mortalities were distributed among six risk classes proportional to model predictions, with 87.7% of mortalities occurring in the top three risk categories. Prioritizing pole retrofitting in the highest-risk areas could prevent >3 x the electrocutions expected by selecting areas at random and would be 89 x more effective than retrofitting in the lowest risk areas. Our risk model offers a consistent method to spatially prioritize retrofitting to increase effectiveness of electrocution reduction for Golden Eagle conservation and provides an efficient approach for utilities. This method of quantifying spatial overlap between indices of exposure and hazard is repeatable and accurate, and can be adapted to various forms of data whenever quantification and visualization of spatial prioritization is desired.