Avian electrocutions on power poles affect raptor populations globally. Mitigation strategies in the USA are typically bottom-up, combining risk assessments for individual poles into a utility-specific avian protection plan. This approach is usually reactive, relying on incidental documentation of electrocutions for initiation, and can allow uncoordinated mitigation strategies among adjacent utilities. A top-down strategy may help solve both problems if maps identifying where distribution power poles occur were available for comparison to range maps for species at risk of electrocution. Range maps exist but pole location data are rarely publicly available in the USA. Pole-density models were previously created for Colorado and Wyoming, the Great Basin, and the Columbia Plateau because pole density can serve as a surrogate for electrocution risk. We used each of these models to predict pole densities throughout four additional areas: the Northwestern Plains, Southwestern Plains, Southwestern Plateaus, and parts of New Mexico not included in other modeled areas. We also applied the Colorado and Wyoming model to portions of the Uinta Basin and Wyoming Basin projecting from Colorado and Wyoming into Idaho and Utah. The Colorado and Wyoming model fit all areas better than other models, except parts of New Mexico not included in other modeled areas, where the Great Basin model fit best. Our model predictions facilitate assessment of pole density across much (2,573,746 km²) of the western USA. To assess whether the models are useful in predicting electrocutions, we compared predicted pole densities throughout White Sands Missile Range to locations of 59 avian electrocutions. Electrocutions occurred at low rates in cells with low predicted pole densities, and at higher rates in cells with moderate and high predicted pole densities. Because the models do not include species-specific information, they have the potential to be applicable to the conservation of a wide variety of species.

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 × the electrocutions expected by selecting areas at random and would be 89 × 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.

Electrocution on overhead electric systems is a primary cause of anthropogenic mortality for Golden Eagles (Aquila chrysaetos) in North America. Distribution poles supporting energized equipment are most often involved in electrocutions, but the frequency with which Golden Eagles perch on pole supporting equipment is unknown. To resolve questions of perch frequency, and by extension, electrocution risk and mitigation prioritization, we used Google Earth to identify perch locations of GPS-transmittered preadult Golden Eagles, and specifically to identify perching on poles supporting transformers. We used transformer poles as a proxy for electrocution risk because transformers are visible in Google Earth imagery. We examined 105 randomly selected “perch events” for each of 10 Golden Eagles (n = 1050 perch events total) tracked for a mean of 16 consecutive mo after fledging. The most frequently used perch sites were cliffs (24.6%), trees (21.2%), and hills (16.6%). Across individuals, 10.8% of perches were on overhead electric systems (individual ranges = 0.0–34.3%). Seven Golden Eagles perched on a distribution pole at least once. Of these, five perched on a transformer pole at least once. Perching on transformer poles occurred more frequently than expected given the proportion of transformer poles present (Yates’ χ² = 26.5, P < 0.001). Given the frequency of perching on transformer poles revealed in this study and the frequency of electrocution on equipment poles revealed in previous studies, the data suggest that electrocution mitigation measures should be focused on equipment poles. Future research should quantify perching across a wider variety of habitats and Golden Eagle age and sex to identify whether the patterns reported here occur more broadly.

We examined variation in the number and demographic composition of electrocuted Saker Falcons (Falco cherrug) in Mongolia. We found 1721 electrocuted Saker Falcons during our surveys of multiple power lines in 2013–2015 and 2018. At a single power line surveyed over a 16-mo period in 2013–2014, the lowest electrocution rates occurred from December to March, with a rise in April coinciding with the return of migrant juveniles from their wintering areas. Electrocution rates rose sharply during juvenile post-fledging dispersal, and then declined in October as migrants departed. Monthly changes in electrocution rate and age profile reflected predicted variation in abundance and age structure of the local Saker Falcon population. We found that 88% of electrocuted Saker Falcons were juveniles, mostly killed during their first calendar year. The sex ratio of electrocuted juveniles fledged in the 2013 cohort (hatch-year birds) was significantly female-biased, in contrast to the equal sex ratio of the 2012 juvenile cohort (second calendar-year birds) killed in the same year (2013). Sex ratio of the 2013 juvenile cohort did not differ significantly from parity at other power lines across Mongolia, indicating that sex ratio of electrocuted juveniles can vary in time and space. The sex of electrocuted adults, predominantly males, and an age profile of breeding Saker Falcons that includes younger females suggests a possible male-biased sex ratio among adult Saker Falcons in Mongolia. Given that large numbers of endangered Saker Falcons are electrocuted annually in Mongolia, our study suggests electrocution may be an important driver of demographic trends that can potentially result in population declines.

Collision with electric lines is a global conservation concern for many birds but raptor species are generally thought to have a low risk of line collision. Collision risk at electric lines is not well understood for Bald Eagles (Haliaeetus leucocephalus), with only incidental reports of collisions in the literature. Line collisions reported for Bald Eagles predominantly occur where lines intersect movement corridors around foraging, roosting, or nesting areas. During five winters from 2014 to 2018, we monitored 602 Bald Eagle crossings of a 230/500-kV transmission line at the Delaware River to determine collision risk. Eagles successfully crossed the line by flying predominantly below the wire zone. There was no difference in flight heights for immature or adult eagles crossing the line. Wire-marking protocols within the electric industry are primarily focused on marking the top plane of wires to alert birds flying above the wires. Additional development of wire-marking options for energized conductors could further reduce collision risk for eagles and other bird species flying below wires. Overall, collision risk appears low for Bald Eagles making localized movements across transmission lines.

Each year from 2012–2016, we conducted helicopter surveys to monitor the distribution, success, and productivity of Golden Eagles (Aquila chrysaetos) breeding within 16 km of California Valley Solar Ranch (CVSR) in San Luis Obispo County, California. This 250-megawatt photovoltaic solar plant was built over 2 yr on 642 ha of disturbed grassland and desert scrub habitat on Carrizo Plain, and was operational in October 2013. Beginning in 2012 coincident with initial CVSR development, the study area and region experienced a severe drought that persisted through the end of the 2016 breeding season. During the study, we detected and monitored 19 variably occupied Golden Eagle breeding territories. We confirmed a similar number of occupied territories in 2012 (15) and 2016 (16), but our ability to reliably confirm pairs declined during the drought and shifting territory dynamics occurred in several areas. Between 2012 and 2015, the proportion of pairs that laid eggs (breeding rate) and fledgling production per occupied territory (productivity) declined by 93–95% (13 pairs laid eggs in 2012; only 1 pair did so in 2015). In 2016, the breeding rate increased sharply again to 63% of occupied territories (87% in 2012) following the return of average rainfall during the preceding winter, but the proportion of pairs that fledged young and productivity rebounded to notably lesser degrees. The eagle breeding rate and productivity trends were strongly correlated with current-year measures of primary plant productivity and rainfall totals from the previous water-year (June–July). Breeding performance metrics for five pairs with territories situated on the periphery of Carrizo Plain and 13 pairs located elsewhere in the study area away from possible development disturbance did not differ statistically. This suggested that CVSR development and initial operation did not adversely affect eagle breeding performance during the study; however, we cannot draw definitive conclusions from this 5-yr study about how CVSR development might have influenced the local eagle breeding population. Instead, we concluded that a severe 5-yr drought dramatically reduced eagle breeding activity in the study area (and region) and confounded our effort to evaluate the effects of the solar development.

Electrocution is a widespread conservation problem for birds of prey that has received little attention in the Neotropics. Here we present electrocution records involving the endangered Chaco Eagle (Buteogallus coronatus) in central Argentina, and we provide information on the power pole structural characteristics associated with electrocutions. Nine Chaco Eagles were recorded electrocuted during the period 2012–2019 over an area of 9000 km². Chaco Eagles were found electrocuted in association with five types of power poles, but more than half the electrocutions (55%) were on poles made of steel-reinforced concrete and with jumper wires above the crossarms. With the addition of four previous electrocution reports in this region during the same time period, the annual rate of Chaco Eagle electrocutions was similar to the rate of mortality by other human-related factors such as direct persecution. Future conservation actions and research should focus on retrofitting the small fraction of poles that pose the highest electrocution risks for Chaco Eagles, and on assessing the demographic effects of electrocution mortality for this species and other endangered raptors in Argentina.

Perch management has historically been used by the electric industry to keep raptors from perching on certain parts of structures that may pose an electrocution risk to birds of prey. In recent times, perch management has been a required mitigation measure for new transmission lines that occur in habitat of the Greater and Gunnison Sage-Grouse (Centrocercus urophasianus and C. minimus, respectively) on lands managed by the Bureau of Land Management and the US Forest Service in an effort to limit the frequency and duration of raptors' perching on transmission and distribution structures including pole tops. In central Wyoming, Tri-State Generation and Transmission Association, Inc. (Tri-State) installed perch deterrents comprising spiked pole caps on pole tops and nest diverters over conductor fittings to manage potential perching and nesting by raptors. An unknown percentage of 59 pole caps were field-modified during installation to fit smaller or larger pole-top diameters than recommended by the manufacturer. The modifications were applied without consulting the biological team that specified and purchased the equipment, or reporting the modifications thereafter. Over 3 yr post-installation, we documented failure of the spikes on the pole caps at an average rate of 0.92 spikes lost per month. Nest diverters (n = 66) installed on these same structures were not modified and did not fail, though nest diverters lacked a protruding spike so were perhaps less prone to failure. Our findings are novel in quantifying potential negative effects to perch-management equipment that is field-modified during installation. This is informative because degradation of perch-management equipment designed to reduce electrocution risk to raptors or reduce raptor predation on prey species of conservation concern may undermine conservation goals. Resource managers working to minimize the environmental impacts of power lines can use this information to better anticipate concerns in power pole retrofitting that may derive from field-modification of retrofitting equipment.

Electrocution on low-voltage power lines is a well-known source of mortality for raptors. Electrocution risk is particularly high for large raptors that can bridge components and make lethal contact, and for raptors living in open landscapes where power poles can be attractive nest or perching sites. Thus, large, grassland-obligate species like the Ferruginous Hawk (Buteo regalis), a legally endangered and threatened species in Alberta and Canada, respectively, are at high risk of electrocution. We used mobile (temporary) versions of artificial nest platforms (ANP) to relocate Ferruginous Hawks nesting on power poles at two sites on Canadian Forces Base Suffield, in Alberta, Canada. At one of these sites an adult female and a fledgling were electrocuted in 2014 and 2015, respectively, prior to introduction of a mobile ANP. In 2016, we relocated this nest to a mobile ANP 23 m away from the original nest pole, and the nesting attempt was successful. In 2017, we installed nest deterrents and insulation on the original nest pole and we installed a permanent ANP 465 m away. From 2017 to 2019, we moved the mobile ANP in stages toward the permanent ANP, with Ferruginous Hawks either nesting on or occupying the mobile ANP each year. We anticipate Ferruginous Hawks transferring to the permanent ANP soon. We also attempted our mobile-ANP-to-permanent-ANP approach at a similar power pole elsewhere on the base in 2016. In 2017, a Ferruginous Hawk pair nested on the permanent ANP so we removed the mobile ANP. This pair did not return in 2018 or 2019. Despite mixed results, use of mobile ANPs as a tool to move nesting raptors away from power poles that are not avian-safe may be a viable electrocution mitigation strategy.

Raptor electrocutions on overhead power lines occur globally. To evaluate a mitigation strategy designed for horizontal post insulators, a common configuration in the 25–69-kV range, we quantified perching by two Great Horned Owls (Bubo virginianus) and seven Red-tailed Hawks (Buteo jamaicensis) on non-energized 25-kV and 69-kV horizontal post insulators installed below vertically mounted perch deterrents. We quantified how often and how long raptors perched on horizontal post insulators beneath perch deterrents, and how often and how long raptors simultaneously contacted both ends of horizontal post insulators, to simulate phase-to-ground electrical contacts. Across 900.0 min of video recordings, raptors usually perched at the distal end of the insulator away from the perch deterrent, but 56 of 1095 perches (5.1%) included at least some time perched below the perch deterrent (Σ = 34.0 min). We never observed any Great Horned Owls simultaneously contact both ends of an insulator. We observed three occurrences of Red-tailed Hawks simultaneously contacting both ends of an insulator (twice on the 25-kV insulator; once on the 69-kV insulator). We speculate that in the absence of the perch deterrents, raptors would have perched toward the center of horizontal post insulators with higher frequency, resulting in a greater frequency of bridging both ends of horizontal post insulators. On energized poles, such behavior would increase electrocution risk. This suggests that perch deterrents may reduce raptor electrocution risk on vertically configured power poles. This study should be repeated with a design that evaluates perching on horizontal post insulators with and without perch deterrents, with larger sample sizes, and with additional raptor species, particularly Golden Eagles (Aquila chrysaetos).

Falconry is commonly used to intimidate and scare off nuisance birds in agricultural areas, at landfills, and at various commercial and industrial sites. We tested the use of falconry in combination with shooting to deter feral Rock Pigeons (Columba livia; hereafter “pigeon”), a nonnative pest species, at a high voltage direct current converter station in southern Alberta. At the station, feral pigeons had occupied three transformer bays at the facility since it came online in 2014, and flock size had grown to an estimated 75–100 individuals by early January 2018. This resulted in operational problems because bird excrement accumulated on equipment and on ground surfaces in the transformer bays. The excrement is toxic and required time-consuming and costly cleanup procedures, including a scheduled power outage. In late January, we undertook a trial abatement program using falconry and shooting with four 3-d site visits between January and April. Falcons, primarily hybrids of Gyrfalcon (Falco rusticolus) and Peregrine Falcon (Falco peregrinus), were flown outside the main converter station building in combination with shooting. After the four visits, the pigeon flock was reduced to fewer than 10 individuals. Less than half of the pigeons were killed by either the falcons or shooting, or a combination of both, and thus we believe the threat of death accounted for the majority of pigeons moving off the site. To prevent the problem from reoccurring, we recommend that pigeon numbers be monitored and the falconry and shooting program be reinitiated if the number of pigeons begins to increase again.