James F. Dwyer

PREVENTING RAPTOR ELECTROCUTIONS IN AN URBAN ENVIRONMENT

ABSTRACT Electrocution of raptors on poles supporting overhead electric lines is a cause of concern in the United States. Techniques for modifying (i.e., retrofitting) potentially lethal poles to reduce electrocutions have been applied in rural areas to poles most likely to be used by raptors. However, raptors also live in urban areas, and criteria for selecting poles to retrofit in towns and cities may differ from those in rural areas. We assessed the effectiveness of using nest sites of Harriss Hawks (Parabuteo unicinctus) in Tucson, Arizona, U.S.A., as a means to focus proactive efforts to retrofit potentially lethal poles. Specifically, we investigated: (1) whether poles close to Harriss Hawk nests were more likely to cause electrocutions than more distant poles with the same configuration; and (2) whether retrofitting poles within 300 m of nests reduced electrocutions in treated areas. We assessed the number of electrocutions before and after retrofitting by searching for electrocuted hawks at a sample of poles. In 2003, we found 23 electrocuted Harriss Hawks within 300 m of nests. The proportion of poles that electrocuted a juvenile Harriss Hawk remained relatively constant from 0 to 300 m from nests. Poles 201–300 m from nests were more likely to electrocute subadult and adult hawks than were poles <200 m from nests. Prior to retrofitting poles, we detected 1.4 electrocutions per monitored nest. After about half of the potentially lethal poles within 300 m of nests were retrofitted, we detected 0.2 electrocutions per nest. For Harriss Hawks in Tucson, risk of electrocution was at least partially related to the proximity of nests to potentially lethal poles. This relationship also may hold for other medium- to large-bodied raptors nesting in urban environments. We recommend that all potentially lethal poles within 300 m of the nests of urban-nesting raptors be retrofitted through the addition of insulation, or through increased spacing between conductors.

ELECTRIC SHOCK INJURIES IN A HARRIS'S HAWK POPULATION

ABSTRACT Electrocution may be an important agent of mortality in many raptor populations, and has been implicated as a contributing factor in the endangerment of some species. In Tucson, Arizona U.S.A. the electrocution of Harriss Hawks (Parabuteo unicinctus) was reported in both the 1980s and 1990s. The latter report also described Harriss Hawks that survived electric shock injuries. From February 2003–May 2004, I captured and examined wild Harriss Hawks in Tucson to investigate whether electric shock injuries might be present in individuals that appeared healthy from a distance. I trapped 85 birds; seven exhibited definite electric-shock injuries, and seven exhibited suspected electric-shock injuries. One individual exhibited injuries not consistent with electric shock. I captured an equal number of males and females, but only one of the injured birds was a male. Females were significantly more likely to have injuries. Whether this difference reflects patterns of initial incurrence of injury, or of higher probability of survival after electric shock remains unresolved. As medium- and large-bodied raptors colonize urban areas where overhead electric systems tend to occur in high densities, those species may also incur increased risk of electrocution.

Collision avoidance by migrating raptors encountering a new electric power transmission line

ABSTRACT Avian collisions with overhead power lines are of conservation concern, particularly in migration corridors. We studied potential collisions where an existing power line supported by towers 20–25 m tall was replaced by the Susquehanna-Roseland line (S-R line), a new line with towers 55–60 m tall. The S-R line crosses Kittatinny Ridge, a corridor for raptors migrating south through New Jersey and Pennsylvania, USA. We hypothesized that the S-R line, which on Kittatinny Ridge includes markers designed to increase its visibility to birds, would cause migrating raptors to react in 1 of 3 ways: (1) to not alter flight elevation, but to pass safely through the S-R wire zone; (2) to not alter flight elevation, and to not pass safely through the wire zone, leading to collisions; or (3) to alter flight elevation and to pass safely above or below the S-R wire zone. To evaluate these hypotheses, we recorded the flight elevations of migrating raptors in 2013 before construction of the S-R line and in 2014 postconstruction. Preconstruction, we recorded 3,698 raptor crossings. Most raptors (72%) crossed above the anticipated S-R wire zone. Some (24%) passed through the anticipated S-R wire zone, and a few (4%) passed below the anticipated S-R wire zone. Postconstruction, we recorded 4,482 crossings. Most raptors (92%) crossed above the S-R wire zone. A few passed through (5%) or below (3%) the S-R wire zone. Postconstruction, raptors responded to the new line by flying higher than they had when traversing the previous line. We did not observe any collisions. Altered flight elevations and the absence of observed collisions supported hypothesis 3. If similar patterns occur at other lines that cross diurnal migration corridors along ridges, then future monitoring may be better focused on potentially riskier settings, such as areas where migrating birds do not have deflected winds to assist with gaining elevation.

Within-Year Survival of Nonbreeding Crested Caracaras

Abstract. Many birds do not breed in the year(s) immediately following independence from parental care. Instead, they spend time as immatures attaining adult plumage and spend time as floaters searching for an opportunity to breed. Floaters are nonbreeding adults. Survival during this period often is poorly understood because immatures and floaters can be secretive and range widely, making them difficult to track. From July 2006 through March 2009, we used radio-tracking data collected by aerial telemetry to estimate survival of 58 nonbreeding Crested Caracaras (Caracara cheriway). Based on an information-theoretic approach, the best-supported models indicated differences in monthly survival, which was lowest (0.953) during the peak of breeding (December–January), slightly higher (0.984) during the remainder of the breeding season (October, November, February, March), and highest (0.995) during the nonbreeding season (April–September). We identified “life stage” as juvenile, immature, or floater on the basis of plumage. We found no effect of sex or life stage on monthly or annual survival, and annual survival was intermediate (0.826) between existing estimates for breeding caracaras (0.876 for males and 0.906 for females) and the dependent juveniles (0.694) of breeding caracaras. None of the birds we tracked nested during our 33-month study. Our findings provide unique insight into reduced survival of nonbreeding individuals during the period when the remainder of the population breeds, and the long-term persistence of individual floaters supports the assertion of previous authors that all breeding habitat is occupied.

Social Hierarchy of Scavenging Raptors on the Falkland Islands, Malvinas

Abstract On the Falkland Islands (Malvinas), raptors historically were perceived as a threat to livestock, and consequently were widely persecuted through the mid-twentieth century. Conservation measures now minimize persecution and have facilitated increases in raptor populations, but the ecology of raptors on the Falkland Islands (Malvinas) remains poorly understood. We investigated social hierarchies within an assemblage of nonmigratory raptorial scavengers: Variable Hawk (Buteo polyosoma), Striated Caracara (Phalcoboenus australis), Southern Caracara (Caracara plancus), and Turkey Vulture (Cathartes aura jota). During thirty observation sessions of 30 min each, we recorded 1386 aggressive interactions involving one or more of these species. We found that Variable Hawks were aggressors in 98% (95% CI  =  96–100%) of interactions with Striated Caracaras, 82% (69–95%) of interactions with Turkey Vultures, and 80% (72–88%) of interactions with Southern Caracaras. Southern Caracaras were aggressors in 100% of interactions with Striated Caracaras, and 90% (80–100%) of interactions with Turkey Vultures. Turkey Vultures were aggressors in 71% (61–82%) of interactions with Striated Caracaras. Within species, we found adult Southern Caracaras were aggressors in 78% (72–84%) of interactions with conspecific juveniles and 76% (68–85%) of interactions with conspecfic subadults. Adult Striated Caracaras were aggessors in 100% of interactions with conspecific juveniles and 97% (91–100%) of interactions with conspecfic subadults. Predicted patterns of size-based dominance typical of complex African and South American avian scavenger assemblages were not observed in the relatively simple assemblage of the Falkland Islands (Malvinas), but we did observe single-species groups of up to 83 Southern Caracaras and 42 Striated Caracaras.

Crippling and Nocturnal Biases in a Study of Sandhill Crane (Grus canadensis) Collisions with a Transmission Line

Abstract. Collisions with power lines are a widely documented cause of avian mortality. Estimating total mortalities from counts of carcasses is usually accomplished by quantifying biasing factors, but neither crippling nor nocturnal biases are well understood. From 4 March through 13 April 2009, data were collected on Sandhill Crane (Grus canadensis) collisions involving a 69-kV transmission line crossing the Platte River in Nebraska, USA, at a major migration stopover area. The line was marked with devices designed to increase visibility to Sandhill Cranes, and thus reduce collisions. Numbers of carcasses detected via traditional searches that involved walking slowly in a zigzag pattern beneath the line were compared to numbers of collisions visually observed through binoculars and night vision spotting scopes and numbers of collisions detected by electronic Bird Strike Indicators (BSI). Seventeen carcasses were found during traditional surveys, 117 collisions were observed visually, and 321 collisions were recorded by BSIs. Most collisions occurred at night, with crippled Sandhill Cranes departing survey transects. Total mortality, including crippling and nocturnal biases, was 2.8 to 3.7 times greater than indicated by a traditional corrected-count mortality estimator. Neither crippling bias nor nocturnal bias were adequately considered by the traditional estimator. Consistent with other studies of avian collision, line marking was only partially successful in reducing collisions.

Critical Dimensions of Raptors on Electric Utility Poles

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 implementation a challenge when a utilitys 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.

Avian Electrocutions on Incorrectly Retrofitted Power Poles

Abstract Avian electrocutions on power poles (hereafter, poles) are a global conservation concern, particularly for large-bodied species like Golden Eagles (Aquila chrysaetos). Retrofitting poles through increasing clearances (separation) between components, adding insulation to components, or adding redirection materials like perch discouragers reduces risk, but electrocutions may occur even on retrofitted poles. We evaluated 52 retrofitted poles where 56 birds, including 17 Golden Eagles, were electrocuted after retrofitting. We used burns on pole equipment and carcasses to identify precise pole-top locations where electrocutions occurred, and we identified three categories of retrofitting errors: product design, mitigation plan, and application. Product design errors (n = 9 poles, 6 Golden Eagles) occurred when products did not sufficiently cover energized equipment. Mitigation plan errors (n = 30 poles, 6 Golden Eagles) occurred when retrofitting plans did not include coverage of all energized components on a pole. Application errors (n = 13 poles, 5 Golden Eagles) occurred when the correct products were installed incorrectly. Retrofitting mistakes were identified in this study retroactively when avian electrocutions occurred on poles described as retrofitted. This is typical of how retrofitting mistakes are identified by the electric industry, which can lead to expensive duplicate efforts, and ongoing avian electrocutions. These can be avoided if retrofitting is done correctly initially. This study provides insight to electric utility personnel and wildlife managers interested in proactively evaluating the thoroughness of retrofitting, facilitating immediate identification and correction of retrofitting errors, increasing cost effectiveness, and reducing avian electrocution mortality.

Correlation of Cere Color with Intra- and Interspecific Agonistic Interactions of Crested Caracaras

Abstract Bright coloration in birds is an important indicator of individual quality often used in social displays. Structural, carotenoid-, and melanin-based colors are long-lasting, widespread, and widely studied. Hemoglobin-based colors are ephemeral, rare, and less studied. Hemoglobin-based displays occur when an individual facultatively enhances or restricts blood flow through caruncles, combs, wattles, or other highly vascularized un-feathered skin patches. In Crested Caracaras (Caracara cheriway; hereafter “caracara”) highly vascularized ceres facultatively undergo immediately reversible hemoglobin-based color changes, hypothesized to correlate with status during contests. I predicted aggressors in contests would consistently display hemoglobin-deprived ceres (hereafter “light”), and receivers would display hemoglobin-enhanced ceres (hereafter “dark”), or vice versa. To test this hypothesis, I conducted 149 30-min group observations during which I recorded outcomes of all observed intra- and interspecific agonistic interactions involving caracaras in groups including up to 46 caracaras (x¯  =  13.4, SD  =  6.9). I recorded 2586 agonistic interactions in which I could identify cere colors and ages of both caracaras involved in an intraspecific interaction (n  =  1160), or of one caracara involved in an interspecific interaction (n  =  1426). Cere colors of caracaras were consistently light when acting as aggressors in intra- and interspecific agonistic interactions, and dark when acting as receivers. Within age classes, caracaras displaying light-colored ceres were consistently aggressors toward caracaras displaying dark ceres, and between age classes, adults with light-colored ceres were aggressors toward younger birds with dark ceres. Caracaras displaying light-colored ceres were aggressors toward Black Vultures (Coragyps atratus) and Turkey Vultures (Cathartes aura) and caracaras with dark ceres were receivers of aggression from these species. Regardless of the cere color, caracaras were subordinate to much larger Bald Eagles (Haliaeetus leucocephalus) and dominant over much smaller American Crows (Corvus brachyrhynchos). My observations support the hypothesis that cere color is correlated with agonistic behaviors and support the signaling hypothesis by correlating specific cere colors displayed with individual roles in intra- and interspecific interactions. CORRELACIÓN DEL COLOR DE LA CERA CON INTERACCIONES AGONÍSTICAS INTRA E INTER-ESPECÍFICAS DE CARACARA CHERIWAY En las aves, la coloración brillante es un indicador importante de calidad individual que se usa a menudo en los despliegues sociales. Los colores estructurales y basados en carotenoides y melanina han sido estudiados desde hace tiempo y de forma amplia y generalizada. Los colores basados en la hemoglobina son efímeros, raros y menos estudiados. Los despliegues basados en la hemoglobina ocurren cuando un individuo aumenta o restringe facultativamente el flujo sanguíneo a través de las carúnculas, crestas u otros parches de piel sin plumas altamente vascularizados. En Caracara cheriway, las ceras altamente vascularizadas experimentan de forma facultativa cambios de color inmediatamente reversibles basados en la hemoglobina, los cuales se piensa que están correlacionados con el estatus durante las competencias. Predije que en una competencia, los individuos agresores desplegarían consistentemente ceras carentes de hemoglobina (de aquí en más “claras”) y que los individuos que reciben la agresión desplegarían ceras realzadas por la hemoglobina (de aquí en más “oscuras”) o viceversa. Para evaluar esta hipótesis, realicé 149 observaciones grupales de 20 minutos cada una durante las cuales registré los resultados de todas las interacciones agonísticas intra e inter-específicas observadas que involucraban a ejemplares de C. cheriway en grupos de hasta 46 individuos (x¯  =  13.4, DE  =  6.9). Registré 2586 interacciones agonísticas en las cuales pude identificar el color de la cera y las edades de ambos individuos involucrados en una interacción intra-específica (n  =  1160), o de un individuo involucrado en una interacción inter-específica (n  =  1426). Los colores de la cera de los individuos fueron consistentemente claros cuando actuaban como agresores en interacciones agonísticas intra e inter-específicas y oscuros cuando actuaban como receptores de la agresión. Dentro de las clases de edad, los individuos que desplegaban ceras claras fueron consistentemente agresivos con individuos que desplegaban ceras oscuras y, entre las clases de edad, los adultos con ceras claras fueron agresivos con aves más jóvenes de ceras oscuras. Los individuos de C. cheriway con ceras claras fueron agresivos con individuos de Coragyps atratus y Cathartes aura y los individuos de C. cheriway con ceras oscuras fueron receptores de agresiones de estas especies. Independientemente del color de la cera, los individuos de C. cheriway fueron subordinados por individuos más grandes de Haliaeetus leucocephalus y dominantes sobre individuos más pequeños de Corvus brachyrhynchos. Mis observaciones apoyan la hipótesis de que el color de la cera está correlacionado con comportamientos agonísticos y apoyan la hipótesis de señalización, correlacionando los despliegues de colores específicos de la cera con los roles individuales en interacciones intra e inter-específicas.

Testing a Supplemental Perch Designed to Prevent Raptor Electrocution on Electric Power Poles

Abstract Electrocution of raptors is an ongoing conservation concern in western North America. Mitigating electrocution risk focuses primarily on insulating energized equipment or increasing the separation between electrical components, but these approaches are not effective on some electric power pole configurations. In some cases, providing a supplemental perch to encourage raptors to perch away from the energized components on a pole may offer a cost-effective alternative. Though numerous supplemental perch designs exist, to our knowledge, raptor responses to them have not been objectively evaluated. To offer an initial quantification of the use of a supplemental perch, we installed a supplemental perch in a flight enclosure at a raptor rehabilitation facility. We then used compositional analysis to evaluate whether and how much rehabilitated raptors used the supplemental perch in a captive setting. The 17 raptors we tested used the supplemental perch 63.3% of the time, used the crossarm below the supplemental perch 3.4% of the time, and used a control crossarm without a supplemental perch 33.3% of the time. These data demonstrate that at least in a captive setting, raptors can be shifted from high-risk perching in the energized zone of a power pole where wires occur, to lower risk perching elsewhere, potentially reducing electrocution risk on some configurations.