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Fort Collins, CO, United States

Lehman R.N.,2023 South Ridge Point Way | Savidge J.A.,Colorado State University | Kennedy P.L.,Oregon State University | Harness R.E.,EDM International Inc.
Journal of Wildlife Management

We estimated electrocution rates for raptors and common ravens (Corvus corax) for the Moon Lake Electrical Association in northeastern Utah and northwestern Colorado, USA. From July 2001 to May 2003, we conducted mortality searches at randomly selected distribution line segments and poles within 3 regions, but rate estimates (0.00360.0112 deaths/pole/yr) may have been biased by the effects of scavengers and by long sampling intervals (≥3 months), which prevented us from determining the cause of death for most birds because of advanced decay. In 20022003, we conducted carcass removal experiments in the Rangely Oil Field (ROF) in northwestern Colorado to estimate scavenging effects, and in 20032004, we reduced sampling intervals to 1 month and searched for dead birds at all distribution poles in the ROF. The shorter sampling interval nearly tripled the number of birds suitable for necropsy, but we were still unable to establish cause of death for >40 of our sample. Instead of eliminating the unknowns from rate estimates, we estimated minimum annual electrocution rates using only confirmed electrocutions and maximum annual electrocution rates based on all available mortalities, including mortalities without known causes. Golden eagles (Aquila chrysaetos) accounted for 63 of dead birds found in 20032004, but they were removed by scavengers at rates well below hawks and owls (6.8 vs. 55.6). We compared maximum rates for the ROF in 20032004 with the rates estimated from a survey conducted at the same poles in 1999 to assess the effects of retrofitting conducted by Moon Lake from 1999 to 2003. Electrocution rates in 20032004 were 47 lower than those in 1999. Raptor densities in the ROF did not change during our study, suggesting the reduction was not the result of changes in raptor populations. However, estimates of raptor densities in 1999 were not available, and we cannot be sure that numbers of birds using the oil field in 1999 were similar to those in 20032004. Our research emphasizes the difficulties of estimating electrocution rates precisely but suggests that utilities will have the greatest effect on mortality by monitoring power lines at large scales and focusing subsequent mitigation efforts in areas that pose the greatest risk to the greatest number of birds. © The Wildlife Society. Source

Harness R.E.,EDM International Inc. | Juvvadi P.R.,Raptor Conservation Foundation
IEEE Industry Applications Magazine

In December 2011, we visited distribution pole lines in the Thar Desert in western India to assess the electrocution risk to raptors. We inspected 624 concrete poles and found 160 bird carcasses at the pole bases. Although power lines can provide positive benefits for birds, the trend of using concrete poles with metal crossarms outweighs the benefits. If concrete poles are used in raptor habitats, alternative construction methods should be substituted, such as the use of suspended insulators. © 1975-2012 IEEE. Source

Dwyer J.F.,Virginia Polytechnic Institute and State University | Dwyer J.F.,EDM International Inc. | Morrison J.L.,Trinity College at Hartford | Fraser J.D.,Virginia Polytechnic Institute and State University
Journal of Wildlife Management

Management of crested caracaras (Caracara cheriway), focuses on nests identified during surveys. If no nests are found, management can be suspended. Thus, false negatives can have substantial consequences. We surveyed 49 breeding territories to assess factors with the potential to cause false negatives in detecting nests of crested caracaras and in observing adult birds. The probability that a nest would be detected on any given visit increased by about 0.5% for each hour of observer experience up to about 70 hours (our maximum). Experience did not affect the probability of observing an adult. The probability of detecting a caracara nest or observing an adult caracara decreased by 2.0-3.5% each hour after sunrise that a visit began. If visibility during any portion of a visit was obscured by fog or rain, the probability of detecting a nest decreased by as much as 60%, and the probability of observing an adult caracara decreased by about 50%. We provide a tool managers can use to calculate the likelihood of successful surveys. We recommend that managers disregard negative results from surveys conducted under conditions that are unlikely to yield positive results, and repeat those surveys under better conditions. © 2011 The Wildlife Society. Source

Dwyer J.F.,EDM International Inc. | Cockwell S.G.,Falklands Conservation
Journal of Raptor Research

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. © 2011 The Raptor Research Foundation, Inc. Source

Dwyer J.F.,EDM International Inc. | Leiker D.L.,Tri State Generation and Transmission Association Incorporated
Wildlife Society Bulletin

Electric utility structures occur widely in natural and human-dominated landscapes and are often used by birds for nesting. Nests can cause power outages, fires, and electrocution of birds and their young, particularly if nests occur directly above energized equipment and incorporate metal wire. Chihuahuan raven (Corvus cryptoleucus) nests often contain metal wire and occur over energized equipment. To explore a proactive risk mitigation strategy we deployed novel nest diverters on 51 structures supporting a 230 kV H-frame transmission line in Kiowa and Bent Counties, Colorado, USA, and compared nesting on these structures with nesting on 66 structures without nest diverters on the same line. Chihuahuan ravens placed nest material on 7% of treated structures and 43% of untreated structures and nested on 0% of treated structures and 34% of untreated structures. Chihuahuan ravens were less likely to attempt to nest on, or actually nest on, structures treated with nest diverters. Future research should evaluate nest diverters over larger spatial and temporal scales and compare prey populations in areas where ravens are excluded to prey populations in areas where ravens persist. © 2012 The Wildlife Society. Source

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