Testing a supplemental perch designed to prevent raptor electrocution on electric power poles.
Key words: buteo, electrocution, perch deterrent, raptor, rehabilitation, supplemental perch
Raptors perching on overhead electric power poles (hereafter poles) can result in electrocution mortalities (APLIC 2006; Dwyer and others 2013) and electric shock injuries (Wendel and others 2002; Dwyer 2006), including incidents in the northwestern US (Harness and Wilson 2001; Harness and Kratz 2007; Dwyer and others 2015). Retrofitting power poles to reduce electrocution risk facilitates transitioning poles from high-risk to low-risk (Dwyer and Mannan 2007; Dwyer and others 2013; Harness and others 2013), with retrofitting priorities defined by an Avian Protection Plan (APP), a program designed to reduce avian electrocution risk on an electric power system (APLIC and USFWS 2005). Retrofitting strategies typically focus on the installation of insulation on, or increasing separation between, energized components and engineered paths to ground (APLIC 2006; Harness and Nielsen 2006; Dwyer and Leiker 2012). However, in some cases installation of insulation or increasing separation between equipment is precluded by the function of the equipment on a pole (APLIC 2006). For example, poles supporting overarm switches are particularly problematic. Overarm switches occur commonly on North American poles, including on poles in the Pacific Northwest, because switch poles allow electricity to be quickly and safely disconnected from and rerouted around emergency situations such as downed power lines, and around planned maintenance such as line replacement. Overarm switches typically have minimal separations between sets of moving components which cannot be cost-effectively covered with insulation. Although APP measures designed to alter avian behavior (for example, supplemental perches or perch deterrents; Dwyer and Doloughan 2014) are not typically as effective as insulation or isolation (APLIC 2006; Dwyer and Mannan 2007), in some scenarios such as overarm switches encouraging raptors to perch elsewhere on a structure may offer a practical strategy to reduce electrocution risk.
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Numerous supplemental perch designs have been installed on power poles in the northwest and throughout the US, but to our knowledge no studies reporting if or how raptors use such perches, or how supplemental perches might be improved, are currently available. To determine whether a commercially available supplemental perch might encourage raptors to shift perching away from the energized zone of a pole where wires are present, we quantified raptor use of a supplemental perch manufactured by Bird Power Line Protection, Ltd (Calgary, Alberta, Canada). The study presented here offers a 1st step in objectively evaluating the potential effectiveness of a risk mitigation strategy offering raptors a perch location above the energized zone on specific poles.
We tested the supplemental perch at the Rocky Mountain Raptor Program (Fort Collins, Colorado), a raptor rehabilitation facility which admits approximately 300 injured, sick, or orphaned wild raptors annually (GEK, MCT, unpub. data). Prior to releasing rehabilitated raptors, the Rocky Mountain Raptor Program places individual raptors in flight enclosures to ensure that they can fly, maneuver, and hunt live prey. We placed 2 wooden mock power poles inside one of these flight enclosures. The flight enclosure was 12.2 m long, 6.1 m wide, and 5.5 m high. The poles were 2.4 m high, with wooden crossarms 2.3 m above ground level, and 2.4 m wide (Fig. 1). Each pole supported a crossarm and 3 insulators, but did not include any wires, switches, or other equipment. We omitted wires and equipment to eliminate concerns that raptors recovering flight skills following injuries might accidentally collide with this equipment in the confined space of the flight enclosure, potentially undermining rehabilitative efforts. Pole framing was consistent with typical US Department of Agriculture Rural Utilities Service specifications used throughout the US in general and the Pacific Northwest in particular. The supplemental perch included a polyvinyl chloride (PVC) perching surface 1.0 m above the pole crossarm (3.3 m high total), and included braces designed to minimize perching in the energized zone of the crossarm. Thus, the treatment pole consisted of a supplemental perch and a shielded crossarm below the supplemental perch (Fig. 2). The control pole simply consisted of a single crossarm 2.3 m above the ground. Because the supplemental perch projected from the top of the pole, the supplemental perch was the highest perch location on either pole, specifically designed to shift raptors from the energized zone around the crossarm to a non-energized zone above. Thus, the increased height of the supplemental perch was a functional component intended to draw raptors away from high-risk locations on a pole.
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To quantify perching, we introduced raptors to the flight enclosure and then waited 24 h before initiating data collection. This allowed raptors to become acclimated to the enclosure, to the mock poles, and to the activities of Rocky Mountain Raptor Program volunteers working in the facility. We then recorded at least 10 perching events over at least 24 h, moved the supplemental perch to the other crossarm, effectively reversing the locations of the treatment pole and control pole, and recorded at least 10 more perching events over at least 24 more hours. This ensured our data reflected raptor preferences regarding the supplemental perch in particular rather than preferences regarding perch locations in the north (more shaded) to south (more sunny) orientation of the flight enclosure. Perch location data were recorded while volunteers at the Rocky Mountain Raptor Program carried out regular duties (such as feeding raptors and cleaning flight enclosures) caring for injured raptors at the facility. When regular duties involved passing near the flight cage containing the mock power poles, volunteers would quickly look inside the enclosure without entering it, and note and record the location of perched raptors.
We staggered data collection over 24 h to minimize lack of independence between sequential observations of perch locations. This approach allowed us to test 2 null hypotheses against an alternate hypothesis. The 1st null hypothesis assumed equal perching on the supplemental perch, the shielded crossarm below the supplemental perch, and the control crossarm without the supplemental perch. In this hypothesis, each perch option was expected to be used 33.3% of the time. The 2nd null hypothesis assumed perching in proportion to the surface area of each perch option. The perching surface at the top of the control crossarm was 2.4 m long by 7.6 cm wide (186 [cm.sup.2]), and was increased by the horizontal surface of the pole-top (25 [cm.sup.2]), creating a total perching surface of 211 [cm.sup.2]. The perching surface at the top of the supplemental perch was 1.8 m long by 7.6 cm wide (139 [cm.sup.2]). The perching surface on the control crossarm below the supplemental perch was reduced by the integrated perch deterrents on the supplemental perch, for a perching surface of 107 [cm.sup.2], including the pole top. These values lead to perch areas composed of the control crossarm (46.2%), supplemental perch (30.4%), and shielded crossarm (23.4%). We compared each null hypothesis to an alternate hypothesis that perching did not occur in proportion to perch availability (that at least 1 perch location was used more than would be expected based on chance alone).
We used compositional analysis (Aebischer and others 1993; Manly 1997) to test our null hypothesis. This ensured that individual raptors were the sampling unit. Compositional analysis implements a log-ratio approach to comparing 2 sets of data. This approach accommodates the unit-sum constraint wherein proportions of use or availability sum to 1 over all resource types (Aebischer and others 1993); in this case perch options. This facilitates comparison of perch events when for any given observation, perching in one place eliminated the possibility of perching somewhere else at the same instant. Compositional analysis may not provide ideal habitat analyses in field studies where available resources are unknown. However, because our resource of interest, perch location on the mock poles, was known with certainty, Compositional Analysis was effective in this study. We used the Microsoft [R] Excel tool ComposAnalysis version 5.1 (Smith Ecology Ltd, Monmouthshire, Wales, United Kingdom) to conduct compositional analysis comparing perch location data between used and available locations. We determined the significance of Wilk's lambda with 1000 iterations, and substituted a value of 0.01 for zero values in the matrix of perch locations (Aebischer and others 1993; Manly 1997).
From March 2014 to February 2015, we introduced 10 Red-tailed Hawks (Buteo jamaicensis; Fig. 3), 3 Swainson's Hawks (Buteo swainsoni), 2 Ferruginous Hawks (Buteo regalis), 1 Rough-legged Hawk (Buteo lagopus), and 1 Turkey Vulture (Cathartes aura) to the test enclosure (n = 17; Table 1). Perch use was disproportional to perch site availability when considering all perches equally ([LAMBDA] = 0.27, [[chi square].sub.2] = 22.10, P < 0.0001), and when considering perches in proportion to surface area ([LAMBDA] = 0.31, [[chi square].sub.2] = 20.12, P < 0.0001). Overall, almost two-thirds (63.3%) of observed perching occurred on the supplemental perch, one-third of perches (33.3%) occurred on the control crossarm, and little perching occurred on the shielded crossarm (3.4%). Three of the raptors tested were in the enclosure during predominantly inclement (snowy) weather; the remainder were in the enclosure during clear to overcast weather with little or no precipitation.
This study demonstrates that rehabilitated buteos and, with less support, Turkey Vultures, will perch in a captive setting on the supplemental perch we tested, suggesting that it may be possible to divert perching from the energized zone of a pole in the wild. Raptors probably chose the supplemental perch based on height relative to the shielded crossarm and the control crossarm, and based on ease of perching relative to the shielded crossarm. Thus, raptor preference for perching on taller structures was capitalized on by offering raptors a perch location above the wire zone where raptors typically perch on poles. Raptors tend to be disproportionately electrocuted on complex poles where wires running pole to pole energize shorter wires connecting pole-mounted equipment such as switches or transformers (Harness and Wilson 2001; APLIC 2006; Dwyer and others 2013). The supplemental perch described here may offer an important alternative risk mitigation strategy for configurations where insulation or isolation are precluded by engineering concerns; for example, on overarm switches, and where limited budgets preclude replacing overarm switches with more raptor-friendly underarm switches.
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Most of our observations occurred when all perches were free of moisture or precipitation. However, some observations occurred during and immediately after snow fell when all perches were wet. Small sample sizes precluded weather-specific analyses, but qualitatively, use of the supplemental perch seemed to decrease when moisture covered the plastic perching surface. Even when dry, raptors sometimes slipped along the PVC surface when landing, resulting in occasional aborted perch events wherein the raptor made a looping flight around the enclosure to try another approach. In the wild, this could result in raptors moving to adjacent poles lacking a supplemental perch. This suggested a potential weakness in the design of the supplemental perch, because electrocution risk tends to increase when raptors and poles are wet (APLIC 2006), a particular concern in areas of the Pacific Northwest. In response to this concern, following the conclusion of this study, Bird Power Line Protection, Ltd. redesigned the supplemental perch to include a wooden, cedar (Cedrus spp.) perching surface designed to increase traction when wet without substantially increasing overall weight, thus eliminating the primary concern associated with a raptor's use of the supplemental perch.
This study is the first to objectively quantify how raptors use a supplemental perch in a captive setting. Future research should evaluate supplemental perches in a field setting within the context of a comprehensive APP which also includes insulation and isolation as mitigation strategies. This unified approach would clarify specific pole types where each mitigation strategy is most effective, allowing resource managers and electric utility operators to better project retrofitting costs, and thus better plan retrofitting priorities.
We thank the volunteers and interns at the Rocky Mountain Raptor Program for collecting the data used in this study. This study was funded by the Rocky Mountain Raptor Program and by EDM International, Inc. Poles and pole-top hardware were donated by Poudre Valley Rural Electric Association (Fort Collins, Colorado). The supplemental perch was donated by Bird Power Line Protection, Ltd.
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Submitted 15 April 2015, accepted 19 August 2015.
Corresponding Editor: D Max Smith.
James F Dwyer
EDM International, Inc., 4001 Automation Way, Fort Collins, CO 80525, USA; jdwyer@ed mlink.com
Michael C Tincher
720 B East Vine Drive, Fort Collins, CO 80524, USA
Rick e Harness
EDM International, Inc., 4001 Automation Way, Fort Collins, CO 80525, USA
Gail E Kratz
720 B East Vine Drive, Fort Collins, CO 80524, USA
TABLE 1. Perch location by species for rehabilitated raptors in a flight enclosure at the Rocky Mountain Raptor Program (Fort Collins, Colorado) exposed to a supplemental perch manufactured by Bird Power Line Protection, Ltd (Calgary, Alberta, Canada). Perch location Supplemental Shielded Control Total perch crossarm crossarm perches Species n Count % Count % Count % Count Ferruginous Hawk 2 7 24 0 0 22 76 29 Rough-legged Hawk 1 5 56 0 0 4 44 9 Red-tailed Hawk 10 130 67 6 3 59 30 195 Swainson's Hawk 3 26 65 4 10 10 25 40 Turkey Vulture 1 18 86 0 0 3 14 21 Total 17 186 63 10 3 98 33 294
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|Author:||Dwyer, James F.; Tincher, Michael C.; Harness, Rick E.; Kratz, Gail E.|
|Publication:||Northwestern Naturalist: A Journal of Vertebrate Biology|
|Date:||Mar 22, 2016|
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