In the United States, the bald eagle Haliaeetus leucocephalus and golden eagle Aquila chrysaetos are managed by the U.S. Fish and Wildlife Service to ensure the species are stable or increasing while allowing for potentially negative effects from anthropogenic sources. Compensatory mitigation, through retrofitting high-risk power poles to reduce electrocutions, can be used to offset negative effects, enabling the U.S. Fish and Wildlife Service to achieve their management objectives of species stability and persistence. Regulators, permit holders, electric utilities, and consultants lack an objective and repeatable method for discriminating between high-risk and low-risk power poles. To illustrate the importance of accurately identifying and retrofitting high-risk poles, we compare conservation benefits among three retrofitting project scenarios: 1) high-risk poles only, 2) a circuit of both low- and high-risk poles, and 3) low-risk poles only. We assert that, in the absence of a common definition of high-risk power poles applied uniformly across the landscape, mitigation approved by the U.S. Fish and Wildlife Service could fall short of its intended value and be unable to meet management objectives. We define high-risk poles in the context of compensatory mitigation as poles in high-quality bald or golden eagle habitat with a relative risk index ≥ 0.40 based on number of phases, number of jumper wires, and presence of pole grounding. We estimate that the conservation benefit of retrofitting a high-risk pole is at least 5.25 times greater than the benefit of retrofitting a low-risk pole. In the long-term, if compensatory mitigation intended to achieve management objectives falls short of its assumed conservation value, the U.S. Fish and Wildlife Service could be forced to limit future permit authorizations until bald or golden eagles can recover from incorrectly calculated conservation benefits. To avoid that negative outcome, we recommend that the U.S. Fish and Wildlife Service set consistent and transparent standards for identifying poles to count as compensatory mitigation credit using our proposed definition of a high-risk power pole.

In pursuit of stable or increasing bald eagle Haliaeetus leucocephalus and golden eagle Aquila chrysaetos populations (USFWS 2016a), the U.S. Fish and Wildlife Service (USFWS) balances its management responsibilities against the needs of commercial and private interests that may incidentally take bald or golden eagles during their normal activities (e.g., electricity generation and transmission, resource extraction, construction, timber harvest, agriculture). The USFWS primarily manages eagle species under the 1940 Bald and Golden Eagle Protection Act (16 U.S.C. 668-668c, as amended) where take is defined as actions to “pursue, shoot, shoot at, poison, wound, kill, capture, trap, collect, or molest or disturb” (USFWS 2009; 2016a). Incidental take is an action that could harm or disturb a bald or golden eagle when “associated with but not the purpose of a [lawful] activity” (USFWS 2009). As anthropogenic activities continue to expand into bald and golden eagle habitat, the USFWS is faced with growing demand for incidental take permits (hereafter “permits”). Permits can authorize “removal, relocation, or destruction” of nests or “disturbance, injury or killing” of individuals (USFWS 2016a). Much of the demand for permits comes from a rapidly growing renewable energy sector where wind and solar facilities are predicted to affect bald and golden eagles (Millsap et al. 2013; Allison et al. 2017).

The 2016 revision of the 1940 Bald and Golden Eagle Protection Act (as amended) represents an evidence-based approach to managing both eagle species and setting take limits (USFWS 2016a). The revision process established background levels for sources of mortality, estimated current and future population levels, created a flyway-based management approach, and revised permitting guidelines for incidental take of bald and golden eagles and their nests. The USFWS manages both eagle species at the population level where a population is defined by geographically designated eagle management units based on migratory bird flyways in North America (i.e., Atlantic, Mississippi, Central, Pacific; USFWS 2016a). There are three golden eagle populations and six bald eagle populations in the United States (USFWS 2016a). The USFWS determined that any authorized incidental take will “be consistent with the goals of maintaining stable or increasing breeding populations in all eagle management units and the persistence of local populations throughout the geographic range of each species” (USFWS 2016a, 2016b). In 2016, bald eagle populations were generally found to be increasing and stable throughout the United States (USFWS 2016c). This trend was recently supported with new estimates indicating that bald eagles have seen a greater than fourfold increase since 2009 (USFWS 2020). Golden eagle populations, however, were found to be stable but forecasted to gradually decrease and therefore be unable to withstand additional take (USFWS 2016c). To ensure no net loss to bald and golden eagles due to authorized incidental take, the USFWS requires permittees to use a mitigation hierarchy to first avoid and minimize their impacts to bald or golden eagles, and, in some cases, compensate for unavoidable residual effects by replacing (“crediting”) a population through mitigation (McKenney and Kiesecker 2010; USFWS 2016b, 2016c, 2016d). Incidental take permits for golden eagles typically require compensatory mitigation.

Compensatory mitigation is a species conservation mechanism wherein authorized incidental take (population debit) is offset by a conservation benefit to the species that increases survival, productivity, or fitness (population credit; USFWS 2016d; Carreras Gamarra and Toombs 2017). For golden eagles, the balance of debits and credits is fundamental to maintaining stable or increasing populations. The USFWS calculates the credits required in each issued permit using a resource equivalency analysis (REA) with a 1.2:1 credit-to-debit ratio for golden eagles and 1:1 ratio for bald eagles (USFWS 2013, 2016a, 2018). If the conservation benefit of the credit provided through compensatory mitigation does not equal or exceed the debit, then the USFWS risks a net loss to a population. Excessive debits or inadequate credits could result in the USFWS limiting, suspending, or eliminating incidental take permits until a population recovers (B. Millsap, USFWS, personal communication). A critical component of meeting the agency's management objective of maintaining stable or increasing bald and golden eagles is to ensure that credits offset permitted incidental take to protect the interests of permitting stakeholders.

The USFWS has explored many anthropogenic sources of bald and golden eagle mortality as potential opportunities to provide credits as compensatory mitigation (USFWS 2016a). For a compensatory mitigation method to be authorized in a permit, the USFWS quantifies, with quantifiable uncertainty, the number of bald or golden eagles credited into a population per year, termed “bird-year” in the REA, per unit of compensatory mitigation. At this time, retrofitting high-risk power poles (HRPPs) is the only method authorized by the USFWS as compensatory mitigation for both bald and golden eagles through incidental take permits, although other mitigation methods are under discussion with applicants (M. Stuber, USFWS, personal communication). The REA is modeled on retrofitting HRPPs and, at present, does not address the comparative value of retrofitting low-risk power poles (LRPPs). Retrofitting of HRPPs was selected because pole retrofitting is a long-established method of mitigating avian electrocution risk within the electric utility industry (Miller et al. 1975; Olendorff et al. 1981; APLIC 2006), and the value of the credit from retrofitting HRPPs is readily calculated from a peer-reviewed study of annual electrocution rates (USFWS 2013).

The rate of avoided loss associated with retrofitting HRPPs was determined to be 0.0036 eagles per pole per y (USFWS 2013) based on the electrocution rate of golden eagles in Lehman et al. (2010). This rate of avoided loss is fundamental to the REA, exerting a strong influence on the number of HRPPs required to be retrofitted to offset the permitted incidental take of any given project. For example, if the rate of avoided loss was hypothetically determined to be 0.0072 eagles per pole per y based on future research, then the number of HRPPs required to be retrofitted to offset a given level of take would be reduced by half.

Power pole retrofits mitigate electrocution risk in bald and golden eagles by 1) increasing clearances between energized and grounded components; 2) insulating pole components; or 3) redirecting perching to safer areas on the pole (APLIC 2006; Dwyer et al. 2017; Mojica et al. 2018). Electrocution risk is unevenly distributed within an overhead electric system and HRPPs generally comprise a small percentage of poles but pose a disproportionate risk of electrocution (Harness and Wilson 2001; Schomburg 2003; Cartron et al. 2005). The primary electrocution risk factors for bald and golden eagles are surrounding habitat and pole configuration (Mojica et al. 2009, 2018; Bedrosian et al. 2020). To identify HRPPs that will fully and reliably offset permitted incidental take when mitigated, it is critical that stakeholders understand the influence these factors exert on electrocution risk.

The USFWS has established administrative procedures to estimate and monitor incidental take in bald and golden eagles but has not set clear standards for HRPP retrofitting as compensatory mitigation, in contravention to the agency's general mitigation policy guidance and Eagle Rule (USFWS 2016a, 2016d). “Equivalent standards” are guidance that ensures equal ecological and procedural mitigation implementation by permittees across all eight USFWS Regions (USFWS 2016a, 2016d). Equivalent standards for HRPP retrofits could benefit USFWS management of bald and golden eagles by standardizing compensatory mitigation across projects and USFWS Regions, bringing the USFWS into compliance with its legal obligations. Ambiguity in the definition of HRPP diminishes the conservation benefit of a compensatory mitigation program if it allows poles with a low risk of causing electrocutions to be retrofitted and credited as if they posed the same risk as HRPPs. Thus, defining and evaluating comparative risk of LRPPs would be useful. As the scale of incidental take permitting and compensatory mitigation grows, setting clear and consistent regulatory guardrails on mitigation actions could help avoid negative effects to both species.

The absence of a regulatory definition of HRPPs is problematic for multiple stakeholders. Regulators could use a clear, evidenced-based HRPP definition to set and enforce permit conditions, and ensure that requirements are consistent across USFWS Regional Offices and permits. Permittees and electric utilities could benefit from clear guidance to accurately and objectively identify HRPPs that qualify for mitigation so that power pole retrofitting fulfills permit conditions. Ultimately, bald and golden eagles, project developers, and the renewable energy industry as a whole will benefit from a clear definition of HRPPs that helps ensure that permitted incidental take is fully offset by power pole mitigation, and the USFWS achieves its overarching management obligations of maintaining bald and golden eagles as stable or increasing. Our objectives were to 1) emphasize the importance of calculating the specific electrocution risk of poles to meet the REA-avoided loss requirements, 2) propose a regulatory definition of HRPPs appropriate for compensatory mitigation, and 3) demonstrate the importance of a clear regulatory HRPP definition in meeting USFWS management objectives for bald and golden eagles by contrasting the conservation benefits of three distinct retrofitting scenarios.

The USFWS REA defines a HRPP as providing a minimum of 0.0036 eagles per pole per y of avoided loss when retrofitted (USFWS 2013, 2018). This avoided loss value originates from a single study of avian electrocution by Lehman et al. (2010) on the Moon Lake Electric Association, Inc. service territory in eastern Utah and western Colorado. The Lehman et al. (2010) data indicate that retrofitting LRPPs has only minor conservation benefit to bald and golden eagles. For compensatory mitigation to meet or exceed the REA-required rate of avoided loss, it is critical to understand the habitat and pole characteristics in Lehman et al. (2010). A nuanced understanding of these variables is fundamental to successfully identifying poles posing a high electrocution risk in different environments and on other overhead electrical systems and to which the 0.0036 eagles per pole per y value derived from Lehman et al. (2010) may appropriately apply.

Quality habitat in the vicinity of a power pole is generally a prerequisite for exposure to electrocution risk (Tinto et al. 2010; Dwyer et al. 2014; Bedrosian et al. 2020). In North America, both eagle species can be found in a wide variety of landscapes including grassland, shrublands, tundra, desert, and forested regions (Buehler 2020, Katzner et al. 2020), though electrocution risk appears to be greater for golden eagles in unforested landscapes with few natural perches and greater for bald eagles when perched adjacent to water bodies (Watts et al. 2015; Mojica et al. 2018). High-quality habitats for golden eagles are relatively undeveloped with abundant prey, predominantly sciurid and leporid species (Bedrosian et al. 2017; Katzner et al. 2020). High-quality habitat for bald eagles includes forest adjacent to open water, concentrations of prey (fish, sciurid, leporid), and proximity to communal roosting sites (Buehler 2020). Assuming bald and golden eagles are more numerous in high-quality habitat, it follows then that electrocution risk is greater within high-quality habitats (Watts et al. 2015; Bedrosian et al. 2020). In Lehman et al. (2010), the Rangely Oil Field, Uintah Basin, and High Desert study areas each were comprised of medium- to high-quality golden eagle habitat (Dunk et al. 2019; Tack et al. 2020), but habitat variability did not fully account for differences in electrocution rates among poles. This finding suggested that habitat is a component of electrocution risk, but habitat alone cannot determine which poles pose a high risk of electrocution. Additional information is needed to determine whether a specific pole is a HRPP.

Pole configuration

Avian electrocution risk varies among poles (Harness and Wilson 2001; Cartron et al. 2005; Ferrer 2012; Dixon et al. 2019). Complex configurations have more wires, pole-mounted equipment, and grounded surfaces (Dwyer and Mojica 2022). Complex poles create high-risk configurations because they have smaller clearances between components, which increases the likelihood a bald or golden eagle will be electrocuted by concurrent phase-to-phase or phase-to-ground contact (Tinto et al. 2010; Guil et al. 2011; Dwyer et al. 2014). Lehman et al. (2010) described intersection and equipment poles as HRPPs (Table 1); these configurations have jumper wires that increase the number of electrocution hazards (Harness and Wilson 2001; Dwyer et al. 2014; Mojica et al. 2018). In the Rangely Oil Field, 70% of golden eagle electrocutions occurred on high-risk configurations, although HRPPs comprised a minority of poles on the system (31%); just 30% of golden eagle electrocutions occurred on LRPPs with no pole-mounted equipment or jumper wires, although LRPPs comprised a majority of poles on the system (69%; Lehman et al. 2010). Lehman et al. (2010) concluded that electrocution rates were greater in the Rangely Oil Field than in the other two study areas (Uintah Basin and High Desert) because pole densities were greater and complex HRPPs were far more prevalent in Rangely, > 50% compared with the other areas (30% and 14%, respectively).

Table 1.

Assignment of an electrocution risk index to high-risk and low-risk power pole (HRRP and LRPP, respectively) configurations in Lehman et al. (2010) using the model in Dwyer et al. (2014) to predict relative risk of electrocution in bald eagles Haliaeetus leucocephalus and golden eagles Aquila chrysaetos.

Assignment of an electrocution risk index to high-risk and low-risk power pole (HRRP and LRPP, respectively) configurations in Lehman et al. (2010) using the model in Dwyer et al. (2014) to predict relative risk of electrocution in bald eagles Haliaeetus leucocephalus and golden eagles Aquila chrysaetos.
Assignment of an electrocution risk index to high-risk and low-risk power pole (HRRP and LRPP, respectively) configurations in Lehman et al. (2010) using the model in Dwyer et al. (2014) to predict relative risk of electrocution in bald eagles Haliaeetus leucocephalus and golden eagles Aquila chrysaetos.

Regional eagle species densities and electrical systems

Electrocution risk varies regionally by species density (Katzner et al. 2020), land cover and topography (Mojica et al. 2018), and density and configuration of poles on an electrical system (Dwyer et al. 2016; 2020). Electrocution risk described in Lehman et al. (2010) represents data from a small geographic area and a single electrical system. A standardized method for classifying electrocution risk of bald and golden eagles throughout North America could be useful in planning retrofitting projects. Irrespective of region or electrical system, it is essential that any permittee or electric utility be able to discriminate between HRPPs and LRPPs to meet the REA-required 0.0036 eagles per pole per y avoided loss standard for compensatory mitigation projects. Ideally the USFWS would be able to audit each retrofitting project to verify that it provides the conservation benefit necessary to meet management objectives.

Dwyer et al. (2014) developed a standardized method (hereafter the “2014 model”) for evaluating avian electrocution risk based on four independent variables: 1) presence of avian habitat surrounding a pole; 2) number of phases; 3) number of jumper wires; and 4) presence of a high ground. The logistic regression model calculates a relative risk index (RRI) for individual power poles on a continuous 0.00–1.00 scale (Dwyer et al. 2014; Harness and Dwyer 2015). The 2014 model can be modified for either bald or golden eagles using the habitat variable and is appropriate for use outside of the original study area (Dwyer and Mojica 2022). For instance, the habitat variable for a golden eagle may include poles near open and unpaved habitat (Dwyer et al. 2014) or habitat with an abundance of a leporid or sciurid prey (Katzner et al. 2020). Thus, the 2014 model is an appropriate tool well suited for discriminating between HRPPs and LRPPs and available as an open-access Excel file (Dwyer et al. 2014). The 2014 model, however, does not categorize poles into “risk bins” but rather ranks them on a continuous scale from 0 to 1. Therefore, a management threshold (between 0 and 1) could be used to separate poles on the landscape into high- and low-risk bins specific to bald or golden eagles. Standardizing the conservation benefit provided by HRPP retrofitting is critical to meeting the USFWS's management objective and, when coupled with a threshold between 0 and 1, the 2014 model provides a means to achieve this end. The Avian Power Line Interaction Committee (APLIC 2006) recommends retrofitting high-risk poles in bald or golden eagle habitat that provide less than 60-in. horizontal or 40-in. vertical clearances. However, these recommendations are nonprescriptive and pole selection is reliant on the utility's discretion. Not all poles with smaller-than-recommended clearances pose an equal electrocution risk. In the context of compensatory mitigation and the USFWS's REA, HRPP retrofitting actions are required to provide 0.0036 eagles per pole per y of avoided loss.

Based on data from an investor-owned utility system in California, the 2014 model is applicable to the full range of overhead electrical systems and habitats found in North America (Dwyer and Mojica 2022), including the Moon Lake Electric Cooperative system in Colorado and Utah. The HRPPs in Lehman et al. (2010) shared the following characteristics: located in high-quality habitat for golden eagles and each had three-phase conductors, at least one jumper wire, and an absent high ground. In the 2014 model, these independent variables result in a minimum RRI of 0.40 (Table 1). Because the REA asserts that retrofitting HRPPs of Lehman et al. (2010) will result in 0.0036 eagles per pole per y of avoided loss, then retrofitting power poles with a minimum RRI of 0.40 elsewhere in North America could also provide 0.0036 eagles per pole per y of avoided loss, consistent with the REA. Thus, based on data from Lehman et al. (2010) and Dwyer et al. (2014), the following definitions are suggested for the USFWS in the context of compensatory mitigation for bald and golden eagles: 1) a HRPP is in high-quality bald or golden eagle habitat and has a RRI of ≥ 0.40; 2) a LRPP is in any habitat and has a RRI of < 0.40.

The Lehman et al. (2010) data demonstrate a large discrepancy in electrocution risk posed by HRPPs and LRPPs. In the Rangely Oil Field, 70% of golden eagle mortalities occurred on HRPPs, which comprised ∼31% of the electrical system. To contrast the risk posed by each type of pole in the Rangeley Oil Field, we derived a dimensionless index by dividing the percentage of mortalities by the percentage of the system for both HRPPs (2.27) and LRPPs (0.43; Table 2). The LRPP index is 0.19 times as large as the HRPP index, indicating that retrofitting one LRPP carries 0.19 times the benefit (< 20%) of retrofitting one HRPP. Conversely, retrofitting one HRPP carries the equivalent conservation benefit to retrofitting 5.25 LRPPs.

Table 2.

Comparative retrofitting benefit for high-risk and low-risk power poles (HRPPs and LRPPs, respectively) based on golden eagle Aquila chrysaetos electrocution mortalities at the Rangely Oil Field, Colorado, documented by Lehman et al. (2010) during 2003–2004. Retrofitting a LRPP to mitigate electrocution risk would provide ∼19% of the avoided loss as retrofitting a HRPP at this site.

Comparative retrofitting benefit for high-risk and low-risk power poles (HRPPs and LRPPs, respectively) based on golden eagle Aquila chrysaetos electrocution mortalities at the Rangely Oil Field, Colorado, documented by Lehman et al. (2010) during 2003–2004. Retrofitting a LRPP to mitigate electrocution risk would provide ∼19% of the avoided loss as retrofitting a HRPP at this site.
Comparative retrofitting benefit for high-risk and low-risk power poles (HRPPs and LRPPs, respectively) based on golden eagle Aquila chrysaetos electrocution mortalities at the Rangely Oil Field, Colorado, documented by Lehman et al. (2010) during 2003–2004. Retrofitting a LRPP to mitigate electrocution risk would provide ∼19% of the avoided loss as retrofitting a HRPP at this site.

The 2014 model provides a standardized method for permittees, utilities, regulatory agencies, and consultants to objectively classify individual poles as HRPPs or LRPPs. Working with a USFWS Regional Office, a proponent would define the area of interest for compensatory mitigation to ensure that all parties agree that the area is high-quality habitat for the permitted species. When candidate poles are identified through a risk assessment, the proponent would submit to the USFWS Regional Office, in spreadsheet format, the number of phases, number of jumper wires, presence/absence of a high ground for each pole, and the RRI of each pole calculated using the 2014 model. The USFWS would then verify that each candidate pole has a RRI ≥ 0.40.

To further illustrate the importance of mitigating only HRPPs, we provide three retrofitting scenarios in the context of a hypothetical USFWS permit authorizing incidental take using golden eagles as the example species. All scenarios share the following assumptions based on REA inputs including direct loss, indirect loss, and productivity rates of the population. First, the incidental take permit authorizes take of one golden eagle in a single year (5 bird-years debited). Second, mitigation owed is 17 HRPPs retrofitted for 30 y (5 bird-years credited), using the 1.2:1 credit-to-debit ratio in the REA model for golden eagles. Third, bird-years debited are offset by bird-years credited where a negative balance would result in a net loss to the golden eagle population. The following retrofitting scenarios illustrate the impact pole selection could have on the conservation success of compensatory mitigation (Table 3).

Table 3.

Example credit ledger for pole retrofitting scenarios where high-risk and low-risk power poles (HRPPs and LRPPs, respectively) are used as compensatory mitigation to offset take of one golden eagle Aquila chrysaetos in a single year. Only scenario 1, where credits are solely generated from HRPPs, produces a balanced credit ledger, and fully offsets permitted take. Number of poles for HRPP and LRPP credit values are shown in parentheses.

Example credit ledger for pole retrofitting scenarios where high-risk and low-risk power poles (HRPPs and LRPPs, respectively) are used as compensatory mitigation to offset take of one golden eagle Aquila chrysaetos in a single year. Only scenario 1, where credits are solely generated from HRPPs, produces a balanced credit ledger, and fully offsets permitted take. Number of poles for HRPP and LRPP credit values are shown in parentheses.
Example credit ledger for pole retrofitting scenarios where high-risk and low-risk power poles (HRPPs and LRPPs, respectively) are used as compensatory mitigation to offset take of one golden eagle Aquila chrysaetos in a single year. Only scenario 1, where credits are solely generated from HRPPs, produces a balanced credit ledger, and fully offsets permitted take. Number of poles for HRPP and LRPP credit values are shown in parentheses.

Scenario 1 – high-risk poles

In the first scenario, a permittee contracts with utility A to retrofit 17 poles to fulfill the mitigation conditions of an incidental take permit. Utility A completes a risk assessment on its system and retrofits 17 HRPPs. In this scenario, all poles meet the REA avoided loss assumptions. The 17 poles provide 5 bird-year credits to the golden eagle population, resulting in no net loss (Table 3).

Scenario 2 – circuit approach (high- and low-risk poles)

Utility B identifies a power line in high-quality habitat that does not provide recommended clearances, and retrofits 17 sequential poles. The circuit is predominantly LRPPs (∼85% poles < 0.40 RRI) with some HRPPs (∼15% poles ≥ 0.40 RRI), so the 17 sequential poles selected are comprised of three HRPPs and 14 LRPPs. Because the LRPPs on the circuit provide reduced conservation benefit, the utility fails to provide the 5 bird-year credit value. In aggregate, the 14 LRPPs (0.19 conservation benefit multiplier, Table 2) and three HRPPs retrofitted provide only 1.56 bird-years of value. This scenario leaves a conservation deficit of 3.44 bird-years, resulting in a net loss (Table 3). Retrofitting in this scenario is unacceptable because additional retrofitted poles are needed to complete the required 5 bird-year credit value.

Scenario 3 – low-risk poles

Utility C retrofits 17 LRPPs (< 0.40 RRI) in high-quality habitat. In this scenario, zero poles meet the REA avoided loss assumptions. Retrofitting these 17 LRPPs provides only 0.95 bird-years of value. This scenario leaves a conservation deficit of 4.05 bird-years, resulting in a net loss (Table 3). Retrofitting only LRPPs is unacceptable because it creates minimal offsets.

Compensatory mitigation is a useful tool allowing federal agencies and their permittees to ensure no net loss to species, even when human effects are unavoidable. Successful compensatory mitigation mechanisms provide a tangible and quantifiable conservation benefit, increasing a species' abundance through habitat improvements, increased productivity, or reduced mortality. Common failures of compensatory mitigation programs include lack of equivalency standards, insufficient management of the mitigation requirement, insufficient funding to complete the mitigation, and incorrect engineering and planning for mitigation (Mead 2008; USFWS 2016d). To avoid failure or inadequacy of compensatory mitigation programs for bald and golden eagles, it is critical that required mitigation credits are consistently offsetting authorized debits across USFWS Regions and permits. To achieve this, we recommend that the USFWS ensure that all stakeholders understand and implement the same standards when identifying HRPP, and HRPPs alone are included in compensatory mitigation requirements under permits. We have proposed a definition herein that we believe will ensure that poles used to offset permitted incidental take of bald and golden eagles will be adequate to meet the USFWS's management objectives.

We expect electrocution mortality rates to decrease as expected if standardized compensatory mitigation guidance is produced and applied uniformly within all USFWS Regions, if HRPPs are selected for retrofitting under permits, and if all these standards are correctly implemented by permittees and utilities. Without this guidance there is a risk that some LRPPs will be selected for retrofitting and a mitigation credit of 0.0036 eagles per pole per y applied in error. As has been shown here and elsewhere (Dwyer and Mojica 2022), if this occurs it is probable that electrocution mortality rates will not be reduced sufficiently across the landscape to offset all permitted take.

A challenge inherent in using HRPP retrofits for compensatory mitigation is the limited data with which to establish the conservation value of a retrofit in the REA; the avoided loss value has been established as 0.0036 eagles per pole per y based on a single peer-reviewed study of golden eagle electrocutions. Some stakeholders have asserted that the USFWS's current way of defining HRPPs is inconsistent and too narrow to be applied nationwide or to both species of eagles. It is likely that the HRPP definition will evolve and improve as additional electrocution-rate data representing new habitats and power distribution systems becomes available. Our paper is heavily based on Dwyer et al. (2014) and Lehman et al. (2010), both of which have weaknesses that could be addressed with additional data sets and research. The electrocution rate used in the REA from Lehman et al. (2010) has some uncertainty from lack of golden eagle density estimates during a portion of the study, inferences made retrospectively on cause of death for some older carcasses, and only one bald eagle electrocution recorded during the study. In the Dwyer et al. (2014) study, neither bald nor golden eagle breeding and nonbreeding space use is readily captured in the 2014 model; instead the habitat variable in the model is used for presence or absence of a species based on habitat type, with no additional weighting for species abundance. Ideally, utilities would already know where pole perching occurs on their system in proximity to nesting territories or prey concentrations to select poles for retrofitting to maximize their potential offsets. Landscape-scale modeling of electrocution risk, as conducted in nesting habitat (Bedrosian et al. 2020), nonbreeding concentration areas (Watts et al. 2015), or high-density pole areas (Dwyer et al. 2016; 2020), could be paired with the 2014 model to locally select poles with the highest electrocution risk for each species.

Understanding the conservation value of a HRPP vs. a LRPP retrofit is critical for REA users because the credit input only applies to HRPPs. Some utility stakeholders have expressed interest in retrofitting a larger number of LRPPs as an alternative to HRPP retrofits. Although the electrocution data in Lehman et al. (2010) could be interpreted as 5.25 LRPP retrofits offering equivalent avoided loss to one HRPP retrofit, this value is highly uncertain; other analyses suggest that the ratio might be closer to 8:1 or even as high as 19:1 (Dwyer and Mojica 2022). It is likely that the value of a HRPP compared with a LRPP retrofit varies between systems because the relative value would be strongly influenced by 1) the proportion of HRPPs and LRPPs, which would affect exposure to each class of pole; 2) specific local construction practices (e.g., securing arrester grounds to brackets or using grounded metal brackets), which increase actual electrocution risk to a greater degree than is accounted for in the 2014 model (Dwyer and Mojica 2022); and 3) other system-specific factors. Additionally, in eagle management units with low electrocution rates or low densities of bald or golden eagles, retrofitting HRPPs may not adequately compensate for authorized take no matter how many poles are mitigated. Mitigating electrocutions is currently the only authorized offset method for incidental take, but in these situations, permittees could be asked to mitigate other sources of mortalities identified in USFWS (2016a).

Avian electrocution data are typically collected opportunistically, and subject to search, scavenger, and other biases; regardless of any correction factors applied, these biases reduce the accuracy of further analyses. The electric utility industry could support additional studies that would provide a gold standard of unbiased, peer-reviewed data. Applying the study design of Lehman et al. (2010), or other unbiased study designs, elsewhere could provide additional data to address utility concerns and develop a broader consensus on an appropriate HRPP definition for compensatory mitigation. In the meantime, the USFWS could benefit if stakeholders wishing to use a different metric to estimate electrocution risk present credible and quantitative evidence that any proposed project will meet or exceed the REA-required 0.0036 eagles per pole per y of avoided loss.

The achievement of management objectives for bald and golden eagles allows the USFWS to continue issuing incidental take permits under the Eagle Rule. Ongoing monitoring could be used to track both the stability of bald and golden eagles and the effectiveness of mitigation. The USFWS continues to monitor both species to adjust incidental take levels and update population models (Millsap et al. 2013; USFWS 2016a, 2021). The USFWS, however, does not currently verify that each retrofitted pole used as compensatory mitigation delivers the expected conservation benefit. We recommend that the USFWS set equivalent standards using the proposed HRPP definition for power pole retrofitting as compensatory mitigation and audit retrofitting projects to ensure that they meet these equivalent standards. In so doing, USFWS will ensure that all retrofitted poles are HRPPs that will fully offset the permitted incidental take of bald and golden eagles.

Please note: The Journal of Fish and Wildlife Management is not responsible for the content or functionality of any supplemental material. Queries should be directed to the corresponding author for the article.

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Reference S5.[USFWS] U.S. Fish and Wildlife Service. 2013. Eagle conservation plan guidance: module 1–land-based wind energy, version 2. Washington, D.C.: U.S. Fish and Wildlife Service.

Available: https://doi.org/10.3996/JFWM-21-045.S5 (2.063 MB PDF) and https://www.fws.gov/birds/management/managed-species/eagle-management.php

Reference S6.[USFWS] U.S. Fish and Wildlife Service. 2016a. Programmatic environmental impact statement for the Eagle Rule revision. Washington, D.C.: U.S. Fish and Wildlife Service.

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Reference S7.[USFWS] U.S. Fish and Wildlife Service. 2016c. Bald and golden eagles: population demographics and estimation of sustainable take in the United States, 2016 update. Washington, D.C.: U.S. Fish and Wildlife Service.

Available: https://doi.org/10.3996/JFWM-21-045.S7 (3.719 MB PDF) and https://www.fws.gov/birds/management/managed-species/eagle-management.php

Reference S8.[USFWS] U.S. Fish and Wildlife Service. 2018. Golden eagle resource equivalency analysis. Washington, D.C.: U.S. Fish and Wildlife Service.

Available: https://doi.org/10.3996/JFWM-21-045.S8 (439 KB XLSX) and https://www.fws.gov/birds/management/managed-species/eagle-management.php

Reference S9.[USFWS] U.S. Fish and Wildlife Service. 2020. Final report: Bald eagle population size: 2020 update. Washington, D.C.: U.S. Fish and Wildlife Service.

Available: https://doi.org/10.3996/JFWM-21-045.S9 (1.008 MB PDF) and https://www.fws.gov/birds/management/managed-species/eagle-management.php

The authors thank the USFWS National Raptor Program and USFWS Regional Office biologists for discussions that led to development of this manuscript. Funding for the analysis and writing was provided by EDM International, Inc and the USFWS's Division of Migratory Bird Management. Conflict of interest statement: EDM International, Inc. provides consulting support to electric utilities implementing avian retrofitting throughout North America and internationally, including retrofitting intended to minimize electrocution risks to bald and golden eagles. We thank J. Dwyer, E. Savage, M. Stuber, G. Williams, B. Millsap, and the Journal's staff and reviewers for comments that improved this work.

Any use of trade, product, website, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

Author notes

Citation: Mojica EK, Eccleston DT, Harness RE. 2022. Importance of power pole selection when retrofitting for eagle compensatory mitigation. Journal of Fish and Wildlife Management 13(1):286–294; e1944-687X. https://doi.org/10.3996/JFWM-21-045

Supplemental Material