Problems Applying a Model for Red-Tailed Hawks and American Crows to Golden Eagles

In the 13(1) issue of the Journal of Fish and Wildlife Management, Dwyer and Mojica (2022) tested the usefulness of a 2014 model, based on Southern California Edison (SCE) data, for assessing avian electrocution risk of power poles to predict electrocution risk for golden eagles Aquila chrysaetos (Dwyer et al. 2014). They suggested that if the 2014 model is applicable to golden eagles, it could be used by the U.S. Fish and Wildlife Service (USFWS) when determining appropriate compensatory mitigation for incidental take permits issued under the Bald and Golden Eagle Protection Act. Power pole retrofits currently serve as mitigation for several types of golden eagle take permits including, but not limited to, wind energy facilities, mining construction and operators, electric utility operators, and nest disturbance. I have the following concerns about the article.

1. In the introduction, the authors discussed golden eagle electrocution by power lines and the potential for using the 2014 model to standardize compensatory mitigation as an offset for permitted incidental take under the Bald and Golden Eagle Protection Act. There is no mention in this section, or elsewhere in the article, that the 2014 model was not useful for predicting golden eagle electrocution risk. The results found predictive modeling worked well for American crows Corvus brachyrhynchos, great horned owls Bubo virginianus, red-shouldered hawks Buteo lineatus, and red-tailed hawks Buteo jamaicensis, but not for common ravens Corvus corax, turkey vultures Cathartes aura, or golden eagles. Dwyer and Mojica (2022) imply the 2014 model worked for golden eagles in Southern California in statements such as this one from the abstract: “We found that although the study population in the 2014 model included relatively few golden eagles, data were sufficient to create a model that can be applied to a target population throughout the western United States.” However, they failed to state that the model does not work well in all geographic areas or with all electric utility systems as indicated by the results in the earlier study using SCE data. Furthermore, in the discussion, the authors did not mention that the 2014 model did not work well for golden eagles when discussing extrapolating the model to other golden eagle populations.

2. Although the 2014 model used SCE data ranging from 1981 to 2009, there was no consultation with SCE during the development of the 2022 article or request for an updated data set. Since 2009, SCE collected more than a decade of additional data that could have been used to either update or test the accuracy of the 2014 model.

3. For the 2014 model, SCE provided the authors with data for transmission voltage fatalities, which included a large percentage of eagle fatalities. However, the authors omitted transmission structures from the model. By simplifying the model to only include distribution structures (identified as 33 kV and below in the 2014 model) the authors send the message that regulatory agencies should focus exclusively on mitigating distribution structures. This message is of concern for utilities, including SCE, because data indicate this approach would be ineffective. Approximately 12% of SCE's circuits are classified as transmission (and subtransmission), with voltages of 55 kilovolts (kV) and higher. However, they account for 41% of golden eagle electrocutions. These data also indicate that golden eagle electrocutions have not occurred on SCE's highest voltage lines (220 and 500 kV). This demonstrates that 41% of golden eagle electrocutions are isolated to the 7% of SCE's circuits with voltages between 55 and 115 kV. This information is valuable because it allows SCE, and perhaps other utilities, to focus its remediation efforts on infrastructure where the greatest benefits will be realized. If agencies rely on a model that discounts transmission voltages of 55–115 kV, such as the one presented in this article, mitigation efforts may miss opportunities to reduce electrocution risk on the structures that would benefit the species the most.

4. The 2022 article reclassified groups of poles in a manner that differed from the 2014 article with no explanation and in a way that is not generally applicable or accepted by electric utilities. Electric utilities typically group distribution poles into two main categories—equipment poles and nonequipment poles—to analyze avian mortality data when developing plans or risk assessments for prioritizing retrofits. The Avian Power Line Interaction Committee (APLIC) is a leader in protecting avian resources in the electric utility industry and the publisher of the most comprehensive guide to reducing avian electrocutions (APLIC 2006). With the inclusion of transmission, chapter 5 of APLIC (2006) breaks structures down into three categories: 1) distribution, 2) transmission, and 3) transformers and other equipment. Treatment of the third category is separate from that of the first two categories that address various problem structure configurations, but lack equipment. Dwyer and Mojica (2022) classified tangent poles as a stand-alone category and grouped several other types of nonequipment poles in the same category as equipment poles, including tangent poles with a ground wire or neutral conductor. The decision to not group poles in a manner accepted by the electric utility industry leads to ambiguity in the development of the article's findings and could cause regulatory agencies to misinterpret results.

5. Many of the studies referenced in Table 1 show golden eagle electrocutions were more common on poles with grounds and jumpers, but not necessarily on poles that would score the highest for risk, such as transformer banks. Dwyer and Mojica (2022) do not show that poles with the largest risk scores would necessarily be the greatest risk for golden eagles. It would be useful to separate poles into three categories rather than two: 1) tangent-no ground, 2) poles with grounds/jumpers-no equipment, and 3) poles with equipment. It is possible that the second category disproportionately affects golden eagles, so fixing poles in this category rather than poles with the largest scores would benefit golden eagles the most.

I believe that the USFWS should limit its use of the 2014 model to determine appropriate compensatory mitigation for eagle take permits and instead work directly with electric utilities interested in providing retrofit poles for mitigation. Each utility could provide historical eagle mortality data, system information, construction practices, and retrofit efforts. These data would then aid in determining areas of greatest potential risk for avian electrocution, which may differ from utility to utility.