Resource Documents: Raptors (6 items)
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Responses of dispersing GPS-tagged Golden Eagles (Aquila chrysaetos) to multiple wind farms across Scotland
Abstract: Wind farms may have two broad potential adverse effects on birds via antagonistic processes: displacement from the vicinity of turbines (avoidance), or death through collision with rotating turbine blades. Large raptors are often shown or presumed to be vulnerable to collision and are demographically sensitive to additional mortality, as exemplified by several studies of the Golden Eagle Aquila chrysaetos. Previous findings from Scottish Eagles, however, have suggested avoidance as the primary response. Our study used data from 59 GPS-tagged Golden Eagles with 28 284 records during natal dispersal before and after turbine operation &ly; 1 km of 569 turbines at 80 wind farms across Scotland. We tested three hypotheses using measurements of tag records’ distance from the hub of turbine locations: (1) avoidance should be evident; (2) older birds should show less avoidance (i.e. habituate to turbines); and (3) rotor diameter should have no influence (smaller diameters are correlated with a turbine’s age, in examining possible habituation). Four generalized linear mixed models (GLMMs) were constructed with intrinsic habitat preference of a turbine location using Golden Eagle Topography (GET) model, turbine operation status (before/after), bird age and rotor diameter as fixed factors. The best GLMM was subsequently verified by k-fold cross-validation and involved only GET habitat preference and presence of an operational turbine. Eagles were eight times less likely to be within a rotor diameter’s distance of a hub location after turbine operation, and modelled displacement distance was 70 m. Our first hypothesis expecting avoidance was supported. Eagles were closer to turbine locations in preferred habitat but at greater distances after turbine operation. Results on bird age (no influence to 5+ years) rejected hypothesis 2, implying no habituation. Support for hypothesis 3 (no influence of rotor diameter) also tentatively inferred no habituation, but data indicated birds went slightly closer to longer rotor blades although not to the turbine tower. We proffer that understanding why avoidance or collision in large raptors may occur can be conceptually envisaged via variation in fear of humans as the ‘super predator’ with turbines as cues to this life-threatening agent.
Alan H. Fielding, Natural Research Ltd, Brathens, Aberdeenshire
David Anderson, Forestry and Land Scotland, Aberfoyle
Stuart Benn, RSPB Scotland, Inverness
Roy Dennis, Roy Dennis Wildlife Foundation, Forres
Matthew Geary, Department of Biological Sciences, University of Chester
Ewan Weston, Natural Research Ltd, Brathens, Aberdeenshire
D. Philip Whitfield, Natural Research Ltd, Brathens, Aberdeenshire
Ibis: International Journal of Avian Science
Published on line ahead of print 20 July 2021. doi: 10.1111/ibi.12996
Author: Law, Peter; and Fuller, Mark
Anthropogenic alterations to landscape are indicators of potential compromise of that landscape’s ecology. We describe how alterations can be assessed as ‘hazards’ to wildlife through a sequence of three steps: diagnosing the means by which the hazard acts on individual organisms at risk; estimating the fitness cost of the hazard to those individuals and the rate at which that cost occurs; and translating that cost rate into a demographic cost by identifying the relevant demographically-closed population. We exploit the conservation-oriented literature on wind farms to illustrate this conceptual scheme. For wind farms, the third component has received less attention than the first two, which suggests it is the most challenging of the three components. A wind farm provides an example of a ‘spatially localized hazard’, i.e., a discrete alteration of landscape hazardous to some population but of which there are some individuals that do not interact directly with the hazard themselves but nevertheless suffer a reduction in fitness in terms of their contribution to the next generation. Spatially localized hazards are identified via the third component of the scheme and are of particular conservation concern as, by their nature, their depredations on wildlife may be underestimated without an appropriate population-level estimation of the demographic cost of the hazard.
Peter R. Law, Centre for African Conservation Ecology, Department of Zoology, Nelson Mandela University, South Africa
Mark Fuller, Forest and Rangeland Ecosystem Science Center, U.S. Geological Survey, Boise, Idaho
Ecological Indicators 94 (2018) 380–385
Download original document: “Evaluating anthropogenic landscape alterations as wildlife hazards, with wind farms as an example”
Author: Hunt, W. Grainger; et al.
Raptors are exposed to a wide variety of human-related mortality agents, and yet population-level effects are rarely quantified. Doing so requires modeling vital rates in the context of species life-history, behavior, and population dynamics theory. In this paper, we explore the details of such an analysis by focusing on the demography of a resident, tree-nesting population of golden eagles (Aquila chrysaetos) in the vicinity of an extensive (142 km²) windfarm in California. During 1994–2000, we tracked the fates of >250 radio-marked individuals of four life-stages and conducted five annual surveys of territory occupancy and reproduction. Collisions with wind turbines accounted for 41% of 88 uncensored fatalities, most of which were subadults and nonbreeding adults (floaters). A consistent overall male preponderance in the population meant that females were the limiting sex in this territorial, monogamous species. Estimates of potential population growth rate and associated variance indicated a stable breeding population, but one for which any further decrease in vital rates would require immigrant floaters to fill territory vacancies. Occupancy surveys 5 and 13 years later (2005 and 2013) showed that the nesting population remained intact, and no upward trend was apparent in the proportion of subadult eagles as pair members, a condition that would have suggested a deficit of adult replacements. However, the number of golden eagle pairs required to support windfarm mortality was large. We estimated that the entire annual reproductive output of 216–255 breeding pairs would have been necessary to support published estimates of 55–65 turbine blade-strike fatalities per year. Although the vital rates forming the basis for these calculations may have changed since the data were collected, our approach should be useful for gaining a clearer understanding of how anthropogenic mortality affects the health of raptor populations, particularly those species with delayed maturity and naturally low reproductive rates.
W. Grainger Hunt, J. David Wiens, Peter R. Law, Mark R. Fuller, Teresa L. Hunt, Daniel E. Driscoll, Ronald E. Jackman
The Peregrine Fund, Boise, Idaho; Predatory Bird Research Group, Long Marine Laboratory, University of California, Santa Cruz; Forest and Rangeland Ecosystem Science Center, United States Geological Survey, Corvallis, Oregon; Centre for African Conservation Ecology, Nelson Mandela Metropolitan University, Port Elizabeth, Republic of South Africa; Forest and Rangeland Ecosystem Science Center, United States Geological Survey, Boise, Idaho; Garcia and Associates, San Anselmo, California; American Eagle Research Institute, Apache Junction, Arizona
PLoS ONE 2017;12(2):e0172232
Download original document: “Quantifying the demographic cost of human-related mortality to a raptor population”
Action on multiple fronts, illegal poisoning and wind farm planning, is required to reverse the decline of the Egyptian vulture in southern Spain
Author: Sanz-Aguilar, Ana; et al.
Large body-sized avian scavengers, including the Egyptian vulture (Neophron percnopterus), are globally threatened due to human-related mortality so guidelines quantifying the efficacy of different management approaches are urgently needed. We used 14 years of territory and individual-based data on a small and geographically isolated Spanish population to estimate survival, recruitment and breeding success. We then forecasted their population viability under current vital rates and under management scenarios that mitigated the main sources of non-natural mortality at breeding grounds (fatalities from wind farms and illegal poisoning). Mean breeding success was 0.68 (SD = 0.17) under current conditions. Annual probabilities of survival were 0.72 (SE = 0.06) for fledglings and 2 yr old non-breeders, 0.73 (SE = 0.04) for non-breeders older than 2 yrs old and 0.93 (SE = 0.04) for breeders. Probabilities of recruitment were 0 for birds aged 1–4, 0.10 (SE = 0.06) for birds aged 5 and 0.19 (SE = 0.09) for older birds. Population viability analyses estimated an annual decline of 3–4% of the breeding population under current conditions. Our results indicate that only by combining different management actions in the breeding area, especially by removing the most important causes of human-related mortality (poisoning and collisions on wind farms), will the population grow and persist in the long term. Reinforcement with captive breeding may also have positive effects but only in combination with the reduction in causes of non-natural mortality. These results, although obtained for a focal species, may be applicable to other endangered populations of long-lived avian scavengers inhabiting southern Europe.
Ana Sanz-Aguilar, José Antonio Sánchez-Zapata, Martina Carrete, José Ramón Benítez, Enrique Ávila, Rafael Arenas, José Antonio Donázar
Dept of Conservation Biology, Estación Biológica de Doñana (CSIC), Sevilla; Population Ecology Group, Instituto Mediterráneo de Estudios Avanzados (CSIC-UIB), Islas Baleares; Área de Ecología, University Miguel Hernández, Alicante; Universidad Pablo de Olavide, Sevilla; Línea de Geodiversidad y Biodiversidad, Agencia de Medioambiente y Agua, Junta de Andalucía, Sevilla; and Gestión del Medio Natural, Dirección Provincial de Córdoba, Consejería de Medio Ambiente, Junta de Andalucía, Córdoba, Spain
Biological Conservation 187 (2015) 10–18. doi: 10.1016/j.biocon.2015.03.029