Critical Dimensions of Raptors on Electric Utility Poles
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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 Birds 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 bird perched on an electric utility pole is at risk of electrocution, with larger species 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 Hawks (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 North America. 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 animal 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 Asia (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 habitat, 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., Canada: Kemper et al. 2013, ting recommendations are available. This potentially Venezuela: McNeil et al. 1985, Siberia: 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