J. Raptor Res. 49(2):210–216 E 2015 The Raptor Research Foundation, Inc.

CRITICAL DIMENSIONS OF RAPTORS ON ELECTRIC UTILITY POLES

JAMES F. DWYER1 EDM International, Inc., Fort Collins, CO 80525 U.S.A.

GAIL E. KRATZ Rocky Mountain Raptor Program, Fort Collins, CO 80524 U.S.A.

RICK E. HARNESS EDM International, Inc., Fort Collins, CO 80525 U.S.A.

SAMANTHA S. LITTLE Audubon Center for of Prey, Maitland, FL 32751 U.S.A.

ABSTRACT.—Avian electrocutions on overhead power structures are a global conservation concern. Size is an important factor influencing whether a perched on an electric utility pole is at risk of electrocution, with larger and larger individuals at greater risk. Ideally, electric poles should protect the largest species (typically Aquila or Haliaeetus species), but protection measures are expensive, making implementa- tion a challenge when a utility’s service area does not include eagles. In these cases, avian protection is sometimes omitted, leaving smaller species at risk because compromise recommendations are unavailable. Flesh-to-flesh distances are a primary determinant of electrocution risk because feathers are only slightly more conductive than air. Metacarpal-to-metacarpal dimensions are particularly important because they quantify the total horizontal distance which can be bridged by the flesh of a bird, but few studies describe metacarpal-to-metacarpal dimensions of at-risk species. Here, we report metacarpal-to-metacarpal and carpal-to-carpal dimensions of 230 raptors of 27 species undergoing rehabilitative care following injury in the wild. Carpal-to-carpal measures facilitate comparison with early efforts by the Avian Power Line Interaction Committee. Our maximum measurements for female Bald Eagles (Haliaeetus leucocephalus), Ferruginous (Buteo regalis), and Red-tailed Hawks (Buteo jamaicensis) exceeded the range previously reported. Wildlife resource managers and electric utility personnel should use metacarpal-to-metacarpal measurements when considering whether a utility pole poses electrocution risk to a particular species. Future research should include reporting these dimensions for at-risk species world-wide so retrofitting recommendations can be further defined beyond .

KEY WORDS: electrocution; morphology; mortality; power pole; raptor; wingspan.

DIMENSIONES CRI´TICAS DE RAPACES EN POSTES DE ELECTRICIDAD

RESUMEN.—Las electrocuciones de aves en estructuras ele´ctricas elevadas son una preocupacio´n global para la conservacio´n. El taman˜o es un factor importante que determina si un ave posada en un poste ele´ctrico esta´ en riesgo de electrocucio´n, siendo las especies de aves ma´s grandes y los individuos de mayor taman˜o los que se encuentran en mayor riesgo. Idealmente, los postes ele´ctricos deberı´an proteger las especies de mayor taman˜o (tı´picamente especies de los ge´neros Aquila or Haliaeetus), pero las medidas de proteccio´n son costosas, haciendo que sea difı´cil implementarlas en a´reas con infraestructuras ele´ctricas donde no hay a´guilas. En estos casos, se omite frecuentemente la proteccio´n de las aves, poniendo en riesgo a las especies ma´s pequen˜as debido a la falta de recomendaciones. Las distancias entre los tejidos vivos del son un factor determinante principal del riesgo de electrocucio´n, debido a que las plumas son so´lo un poco ma´s conductivas que el aire. La distancia de metacarpo a metacarpo es particularmente importante porque cuantifica la distancia horizontal total que puede ser puenteada por la carne del ave, pero pocos estudios describen las dimensiones de metacarpo a metacarpo de las especies en riesgo. En este estudio presenta- mos las dimensiones de metacarpo a metacarpo y de carpo a carpo de 230 aves rapaces de 27 especies que

1 Email address: [email protected]

210 JUNE 2015 CRITICAL DIMENSIONS OF RAPTORS 211

se encuentran en tratamiento de rehabilitacio´n debido a lesiones sufridas en libertad. Las medidas de carpo a carpo facilitan la comparacio´n con los primeros esfuerzos del Comite´ de Interaccio´n entre Aves y Lı´neas Ele´ctricas. Nuestras medidas ma´ximas para hembras de Haliaeetus leucocephalus, Buteo regalis y Buteo jamaicensis excedieron los rangos mostrados previamente. Los encargados de la gestio´n de vida silvestre y el personal de las compan˜ı´as ele´ctricas deberı´an utilizar las medidas de metacarpo a metacarpo para con- siderar si un poste ele´ctrico presenta un riesgo de electrocucio´n para una especie en particular. En un fututo, las investigaciones deberı´an incluir el registro de estas dimensiones para las especies en riesgo a nivel mundial. De esta manera, las recomendaciones de mejora pueden ser definidas de mejor manera ma´s alla´ de Ame´rica del Norte. [Traduccio´n del equipo editorial]

Negative interactions between birds and overhead to-foot length of a bird (APLIC 2006). Thus, larger electric systems are a global and persistent conserva- species, and larger individuals within species, with tion concern (Janss 2000, APLIC 2006, Angelov et al. larger flesh-to-flesh distances, are more commonly 2013). Problem interactions include electrocutions electrocuted than smaller birds. To minimize elec- (Harness and Wilson 2001, Dwyer and Mannan trocution risk during takeoff and landing, APLIC’s 2007, Dwyer et al. 2013b), electric shock injuries (2006) foundational work identified 152 cm hori- (Dwyer 2006, Fox and Wynn 2010), and collisions zontal separation as a critical dimension necessary (Martin and Shaw 2010, Sporer et al. 2013, Rogers to minimize electrocution risk on distribution struc- et al. 2014). Electrocutions on, or collisions with, tures for Bald Eagles (Haliaeetus leucocephalus) and overhead power lines are believed to have contribut- Golden Eagles (Aquila chrysaetos). Because these di- ed to population declines of Egyptian Vultures (Neo- mensions should accommodate safe perching by phron percnopterus) in East Africa (Angelov et al. the largest North American raptors, smaller birds 2013), Ludwig’s Bustard (Neotis ludwigii) in South should also be protected in typical situations. To Africa (Jenkins et al. 2011), Spanish Imperial Eagles our knowledge, no researchers have quantified sim- (Aquila adalberti) in the Iberian Penisula (Gonza´lez et ilar critical dimensions for species outside of North al. 2007), and multiple raptors in (Karyakin et al. America. 2009, Dixon et al. 2013). Electrocution may also have Electric utilities must use limited budgets to great- affected the social ecology of Harris’s Hawks (Para- est effect (Harness and Wilson 2001, Dwyer and Man- buteo unicinctus) in North America (Dawson 1988). nan 2007). In cases where a utility’s service area does Though population-level effects have not been dem- not contain eagle , the utility sometimes omits onstrated for most species, concern over electrocu- avian protection because recommended practices are tion and collision mortality nevertheless persists for prohibitively expensive and no compromise retrofit- birds worldwide (e.g., : Kemper et al. 2013, ting recommendations are available. This potentially Venezuela: McNeil et al. 1985, : Goroshko leaves non-eagle species at risk of electrocution. Just 2011, Saudi Arabia: Shobrak 2012). In addition to as eagle-specific retrofitting measures are developed concerns regarding avian populations, electrocu- for eagle-specific concerns (Jenkins et al. 2013), ret- tions can be costly to electric utilities and place hu- rofitting measures designed to protect smaller spe- man health and safety at risk when incidents cause cies in non-eagle habitat could result in more wide- power outages (Harness and Wilson 2001, Dwyer et spread retrofitting by electric utilities. al. 2013b, Jenkins et al. 2013), equipment failures Because electrocution risk is strongly influenced (Van Rooyen et al. 2003, APLIC 2006), and fires by avian dimensions, detailed knowledge of species- (Lehman and Barret 2002, Tinto´ et al. 2010). Thus, specific morphology is needed to identify species- wildlife managers and the electric industry share specific high-risk poles and mitigation measures a common goal in preventing avian electrocutions. (Janss 2000). To date, only APLIC (2006) describes Because dry feathers are only slightly more con- species-specific morphology specifically focusing on ductive than air (APLIC 2006), electrocution risk electrocution risk, and that resource is based on occurs when horizontal separation between differ- small numbers (1–10 individuals per species [x¯ 5 ently energized conductors, or conductors and 4.1, SE 5 1.0] for 12 species from which carpal-to- ground(s) is smaller than the metacarpal-to-meta- carpal dimensions are reported). This is true pre- carpal (flesh-to-flesh) distance of a bird’s wingspan, sumably because flesh-to-flesh distances, which are or when vertical separation is smaller than the head- important to electrocution risk but of little use 212 DWYER ET AL.VOL. 49, NO.2

Figure 1. A. Metacarpal to metacarpal measurement location. B. Carpal to carpal measurement location. Grey shading indicates flesh of wing. Wing must be fully extended when measurements are made. otherwise, are not typically collected by raptor biol- Birds of Prey receives raptors from throughout Flor- ogists. This has led to broad extrapolation of critical ida, U.S.A. Because raptors were included in this dimensions to areas where species sizes differ from research only within strict rehabilitation guidelines those of source data (as in Harness et al. 2013). designed to maximize successful return to the wild, Because the APLIC (2006) sample sizes are relative- all procedures described herein complied with the ly small, and because substantial variation exists ethical standards and institutional guidelines for within species, additional data to describe a broader ameliorating suffering in raptor rehabilitation in range of variation within and among species should the United States (Miller 2000). Each measured rap- improve our ability to protect raptors. Our objective tor was successfully rehabilitated and released, died in this report was to describe metacarpal-to-meta- of injuries incurred prior to admittance, or was eu- carpal and carpal-to-carpal dimensions of raptors. thanized because injuries could not be effectively Metacarpal-to-metacarpal dimensions may provide treated. the most direct assessment of maximum flesh-to- To collect measurements (Fig. 1), we placed flesh breadth for a bird, and carpal-to-carpal dimen- each bird on its back, fully extended the wings, sions allow comparison to APLIC (2006). and recorded (1) the distance between the location where the skin ended and the #10 primary feather METHODS began on one wing and the same location on the From 1 April 2012, through 31 October 2013, we opposite wing (metacarpal-to-metacarpal), and (2) measured metacarpal-to-metacarpal and carpal-to- the distance between the carpal joint on one wing carpal distances from 199 injured wild raptors trea- and the carpal joint on the opposite wing (carpal- ted at the Rocky Mountain Raptor Program (Fort to-carpal). We did not measure birds that had lost Collins, Colorado) and 31 raptors treated at the Au- full extension of both wings due to injury or am- dubon Center for Birds of Prey (Maitland, Florida) putation. We identified the sex of each bird by raptor rehabilitation facilities (n 5 230). The Rocky plumage, mass, or if rehabilitation was unsuccess- Mountain Raptor Program receives raptors from ful, through observation of testes or ovaries during throughout Colorado, western Nebraska, and south- necropsy. We recorded dimensions for relatively eastern , U.S.A. The Audubon Center for small raptors, because measurements for smaller JUNE 2015 CRITICAL DIMENSIONS OF RAPTORS 213

Table 1. Critical dimensions of raptors (metacarpal-to-metacarpal $1000 cm) admitted to the Rocky Mountain Raptor Program, Fort Collins, Colorado, from 1 April 2012 through 31 October 2013, or the Audubon Center for Birds of Prey, Maitland, Florida, from 31 March 2013 through 31 October 2013.

METACARPAL-TO- a CARPAL-TO-CARPAL METACARPAL C–C WITHIN (C–C) (M–M) APLIC (2006) ESTIMATESb MEAN MAX SEe MEAN MAX SEe SPECIESc SCIENTIFIC NAME SEXd n (cm) (cm) (cm) (cm) (cm) (cm) MEAN MAX American Falco sparverius F 17 19.6 23.0 0.6 25.9 32.0 0.7 y y M 15 17.7 19.8 0.5 24.2 28.4 0.6 – – Bald Eagle Haliaeetus leucocephalus F 1 88.7 88.7 – 112.2 112.2 – n n M 3 82.8 84.0 0.8 108.4 112.0 2.3 y y U 1 81.0 81.0 – 108.0 108.0 – y y Barn Owl Tyto alba F 3 41.9 49.6 5.3 46.9 58.4 5.9 y y Barred Owl Strix varia M 3 44.2 49.0 2.5 56.7 60.0 2.0 – – U 1 48.0 48.0 – 60.0 60.0 – – – Black Vulture Coragyps atratus U 3 59.3 63.5 2.1 78.7 79.4 0.4 – – Broad-winged Buteo platypterus F 1 31.0 31.0 – 44.6 44.6 – – – Burrowing Owl Athene cunicularia F 1 18.8 18.8 – 24.2 24.2 – – – M 1 22.2 22.2 – 27.7 27.7 – – – Cooper’s Hawk cooperii F 10 31.2 38.0 0.8 42.6 48.0 1.2 – – M 3 24.6 25.9 0.8 32.2 34.4 1.1 – – U 2 27.7 29.0 1.3 36.8 37.8 1.0 – – Eastern Screech-Owl Megascops asio F 1 26.8 26.8 – 34.2 34.2 – – – M 1 21.4 21.4 – 29.4 29.4 – – – Ferruginous Hawk Buteo regalis F 3 50.9 62.0 6.4 69.1 80.0 6.7 y n M 1 51.2 51.2 – 67.3 67.3 – y y Golden Eagle Aquila chrysaetos U 1 75.0 75.0 – 102.0 102.0 – y y Great Bubo virginianus F 20 51.2 59.0 1.3 68.0 85.6 2.2 y y M 13 47.1 56.0 1.2 64.0 76.0 2.2 y y U 2 50.5 57.0 6.5 68.8 77.8 9.0 y y Long-eared Owl Asio otus F 2 28.8 33.6 4.8 41.8 47.6 5.8 – – M 2 25.9 28.7 2.9 35.1 37.2 2.1 – – Falco columbarius M 1 21.2 21.2 – 31.2 31.2 – – – Mississippi Kite Ictinia mississippiensis M 4 29.7 32.0 1.2 38.2 42.0 1.4 – – Accipiter gentilis M 1 45.0 45.0 – 59.8 59.8 – – – Northern Harrier Circus cyaneus M 2 35.2 35.6 0.4 44.3 51.0 6.8 – – Northern Saw-whet Owl Aegolius acadicus F 1 18.6 18.6 – 20.6 20.6 – – – M 1 23.6 23.6 – 28.0 28.0 – – – Osprey Pandion haliaetus F 4 66.6 70.3 2.4 86.5 100.0 6.0 – – M 7 62.1 69.0 1.8 82.0 88.0 2.1 – – U 1 67.7 67.7 – 88.9 88.9 – – – Peregrine Falco peregrinus F 1 40.0 40.0 – 58.0 58.0 – y y M 1 34.0 34.0 – 56.0 56.0 – y y Red-shouldered Hawk Buteo lineatus F 2 41.6 43.2 1.6 53.2 53.3 0.2 – – M 4 37.3 41.0 1.7 49.5 53.0 1.8 – – Falcon Falco mexicanus M 2 31.3 31.5 0.3 42.0 46.6 – n n Red-tailed Hawk Buteo jamaicensis F 16 47.1 58.4 1.3 62.7 73.6 1.5 y n M 22 44.4 55.0 1.1 59.4 72.0 1.6 y y U 2 46.8 47.6 0.8 62.3 66.6 4.3 y y Rough-legged Hawk Buteo lagopus F 1 42.4 42.4 – 57.2 57.2 – – – Sharp-shinned Hawk Accipiter striatus F 1 17.2 17.2 – 23.8 23.8 – – – M 2 18.8 19.3 0.5 22.5 24.1 1.6 – – 214 DWYER ET AL.VOL. 49, NO.2

Table 1. Continued.

METACARPAL-TO- a CARPAL-TO-CARPAL METACARPAL C–C WITHIN (C–C) (M–M) APLIC (2006) ESTIMATESb MEAN MAX SEe MEAN MAX SEe SPECIESc SCIENTIFIC NAME SEXd n (cm) (cm) (cm) (cm) (cm) (cm) MEAN MAX Swainson’s Hawk Buteo swainsoni F 2 50.9 54.5 3.7 65.9 67.4 1.6 y y M 16 41.0 49.0 1.0 53.2 61.0 1.6 – – Turkey Vulture Cathartes aura M 3 60.5 61.1 0.4 72.5 73.2 0.6 y n a See text and Figure 1 for description. b Comparison to APLIC measurements 5 ‘‘–’’ indicates APLIC 2006 does not include the reported species. c All species except Burrowing Owl, Broad-winged Hawk, Northern Saw-whet Owl, and Sharp-shinned Hawk are reported in APLIC (2006) as having been electrocuted, as least infrequently. d F 5 female, M 5 male, U 5 unknown. e SE 5 ‘‘–’’ indicates only one individual was measured. raptors may be relevant in areas where large raptors considerations must also be recognized. If eagle hab- are unlikely, because even small raptors are occa- itat is absent in the service area of a utility that is unable sionally electrocuted (Janss 2000), and because to support the financial burden of retrofitting to AP- smaller non-raptors, such as American Crows (Cor- LIC (2006) standards, then retrofitting to protect vus brachyrhynchos; Dwyer et al. 2013b) and House smaller birds might offer an important intermediate Crows (Corvus splendens; Harness et al. 2013) are step to fully protecting an overhead system, or allow regularly electrocuted. All measurement results more poles within a system to be retrofitted for local are mean 6 SE unless otherwise indicated. We species at risk of electrocution. evaluated critical dimensions separately by sex with- APLIC (2006) pioneered the use of avian dimen- in species because sexual size dimorphism has been sions for understanding electrocution risk. Here, we related to differences in the sex-ratio of electrocut- report the first metacarpal-to-metacarpal measure- ed birds (Ferrer and Hiraldo 1992, Dwyer and ments for birds at risk of electrocution. Metacarpal- Mannan 2007). to-metacarpal dimensions are particularly important because they quantify the total horizontal distance RESULTS which can be bridged by the fleshy parts of a bird. We recorded dimensions of 230 raptors of 27 spe- Wing length or wingspan might serve as a proxy for cies (Table 1). Eleven species we measured were also electrocution risk if the relationship between these included in APLIC (2006). Of these, five included at measures and metacarpal-to-metacarpal measure- least one individual larger than the carpal-to-carpal ments were known, but these relationships are typi- measurements reported in APLIC (2006). These cally unknown, so use of standard measurements in were female Bald Eagle, female Ferruginous Hawk identifying electrocution risk by species may not suc- (Buteo regalis), male (Falco mexicanus), cessfully mitigate electrocution risk. Thus, we recom- female Red-tailed Hawk (Buteo jamaicensis), and male mend building on the APLIC (2006) foundation by Turkey Vulture (Cathartes aura). None of the species measuring metacarpal-to-metacarpal dimensions for we recorded were listed as threatened or endangered species at risk of electrocution around the world. in the U.S.A. at the time of our study. Our maximum carpal-to-carpal measurement ex- ceeded previous ranges reported (APLIC 2006) for DISCUSSION five species. We believe this is a result of the limited Raptor presence and distribution is dynamic, with sample sizes included in APLIC (2006). However, the life cycles of many species including migrations our data are also drawn from limited sample sizes or juvenile dispersal through nonbreeding habitat for all species evaluated. Even the most abundant (Sergio et al. 2009, Schindler et al. 2012, Dwyer et al. species we measured, Red-tailed Hawk and Great 2013a). Ideally, retrofitting measures would be ap- Horned Owl (Bubo virginianus) were drawn from plied universally to protect the largest species even ranges limited by the permits issued to the rehabil- outside their typical habitat. However, practical itation centers where we worked, not by biologically JUNE 2015 CRITICAL DIMENSIONS OF RAPTORS 215 relevant boundaries. Thus, neither the APLIC (2006) China (Dixon et al. 2013), minimizing electrocution samples, nor the samples reported here, likely quan- risk by increasing separation may be impractical be- tify all the variation in critical measurements, and cause the financial resources required to reframe both are limited to North American species. Because poles may exceed available budgets. In these cases, Bald Eagles, Ferruginous Hawks, and Red-tailed covering energized equipment with insulation is Hawks have been widely reported in electrocution necessary to protect raptors and other avian species literature (Harness and Wilson 2001, APLIC 2006), from electrocution. Materials designed to minimize the lack of information on critical dimensions in electrocution risk in these cases must be carefully these species, even including our own results, indi- fitted to intended equipment or the retrofitting may cates that future researchers should quantify meta- not be effective. Knowledge of critical dimensions of carpal-to-metacarpal and standing height measure- birds likely to perch on these structures would facil- ments for a much larger sample of individuals. We itate precise identification of locations where insula- did not collect measurements of standing height. tion is required. Thus, APLIC (2006) and inference of height made Avian electrocution is a global concern requiring from height-length correlations (as in Janss 2000), species-specific and power line-specific mitigation remain the only available measure of vertical separa- approaches. Wildlife rehabilitation centers are wide- tion required to minimize avian electrocution risk. ly distributed around the world. Data collected at Future research should include height from the bot- rehabilitation centers can be particularly informa- tom of the foot to the top of the head on live stand- tive because birds treated at these centers often ing birds, particularly for tall species, which may be at originate from much larger areas than field studies greater risk of head-to-foot electrocution risk. can accommodate (Kalpakis et al. 2009). This re- Retrofitting can be accomplished through increas- port serves as an example of how wildlife rehabilita- ing separation between energized equipment, or tors can contribute to long-term solutions by pro- through covering energized equipment. In North viding information on how power lines should be America, APLIC (2006) identified 152 cm of hori- designed to prevent avian injuries. zontal separation and 102 cm of vertical separation as ACKNOWLEDGMENTS critical distances necessary to minimize electrocution risk on distribution structures for Bald Eagles and This study was funded by EDM International, Inc., the Rocky Mountain Raptor Program (RMRP), and the Audu- Golden Eagles. Similar critical dimensions, supported bon Center for Birds of Prey (ACBP). We thank J. Scherpelz by data on metacarpal-to-metacarpal, and head-to-foot for access to raptors at RMRP. We thank D. Flynt, R. Stock, M. measurements, should be identified for other regions Tincher, and the interns of the Rocky Mountain Raptor Pro- where avian electrocution concerns persist, but these gram and the Audubon Center for Birds of Prey for assistance collecting data. We thank H. Bates for creating Figure 1, and critical dimensions will not protect all species in all P. Lo´pez-Lo´pez, A. Dwyer, D. Eccleston, and three anony- cases. Raptors such as Harris’s Hawks, which can be mous reviewers for comments improving the manuscript. electrocuted when multiple individuals perch together We conducted this work under U.S. Fish and Wildlife permits on a single pole (Dwyer and Mannan 2007), non- MB725655-4 and MB672801, Colorado Parks and Wildlife raptors with very long necks and , such as storks permit REH277A2104, and Florida Fish and Wildlife Conser- vation Commission permit WLR-15-0019. (Janss 2000, Garrido and Ferna´ndez-Cruz 2003), and corvids that use their beaks to probe under insulation LITERATURE CITED are also electrocuted (Cartron et al. 2000, Dwyer et al. ANGELOV, I., I. HASHIM, AND S. OPPEL. 2013. Persistent elec- 2013b, Harness et al. 2013), and numerous species are trocution mortality of Egyptian Vultures Neophron perc- at risk when nesting on power poles (APLIC 2006, nopterus over 28 years in East Africa. Bird Conservation Dwyer and Leiker 2012, Jenkins et al. 2013). Because International 23:1–6. of the unique morphology and behaviors of these spe- APLIC (AVIAN POWER LINE INTERACTION COMMITTEE). 2006. cies, the critical dimensions described here likely will Suggested practices for avian protection on power not prevent their electrocution. Thus, though critical lines: the state of the art in 2006. Edison Electric In- dimensions are useful, additional species-specific ret- stitute, APLIC, and the California Energy Commission, , DC and Sacramento, CA U.S.A. rofitting is needed in some areas. CARTRON, J.-L.E., G.L. GARBER,C.FINLEY,C.RUSTAY, R.P. Where poles are constructed with grounded KELLERMUELLER, M.P. 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