Golden Eagles Aquila Chrysaetos Research Articles

Using juvenile movements as a proxy for adult habitat and space use in long‐lived territorial species: a case study on the golden eagle

Effective conservation management of wildlife species depends on understanding their space and habitat use. Telemetry has become the primary source of data for information on how species use space and habitats. However, animals can be difficult to capture, leading to limited sample sizes and thus low quality inferences. As some individuals may be easier to capture than others, it may be tempting to use them to make inferences about the studied population as a whole. Juvenile birds, in contrast to adults, are easy to capture while they are still in the nest. However, there are few studies on when and how they might serve to obtain a representative characterization of the habitat or space use of adults. This study investigated this by using GPS‐tracking data of 35 adult/juvenile dyads of golden eagles Aquila chrysaetos, with the juvenile and adult in a dyad sharing the same home‐range. We assessed juvenile‐to‐adult home‐range overlap and also compared their relative use of habitats within that space. We also analysed how these metrics evolved throughout the post‐fledging dependence period (PFDP). During this period, juvenile‐to‐adult similarity was more than 80% for the entire home‐range, whereas it was lower for the core area (approximately 60%). Habitat‐use similarity was high, at approximately 90% for both the home‐range and core area, both in land‐cover and topography. The similarity increased following the improvement of juvenile flight skills over a period of two months, to the extent that two months after fledging and until the end of the PFDP, habitat and space use of juveniles can be used to infer the home‐range and habitat requirements of adults. It would be valuable to study this ‘adult‐by‐juvenile replacement' approach in other species to determine whether it could be generalized, notably for species with a shorter dependence period or more complex social interactions.

Golden Eagle Populations, Movements, and Landscape Barriers: Insights from Scotland

GPS satellite tracking allows novel investigations of how golden eagles Aquila chrysaetos use the landscape at several scales and at different life history stages, including research on geographical barriers which may prevent or limit range expansion or create population/sub-population isolation. If there are significant barriers to golden eagle movements, there could be demographic and genetic consequences. Genetic studies have led investigations on the identification of sub-species, populations, and sub-populations but should be conjoined with demographic studies and dispersal movements to understand fully such designations and their geographic delimitation. Scottish eagles are genetically differentiated from continental European birds, with thousands of years of separation creating a distinct population, though without sub-species assignation. They present unique research opportunities to examine barriers to movements illustrated by satellite tracking under Scotland’s highly variable geography. We primarily examined two features, using more than seven million dispersal records from satellite tags fitted to 152 nestlings. The first was the presence of unsuitable terrestrial habitat. We found few movements across a region of largely unsuitable lowland habitat between upland regions substantially generated by geological features over 70 km apart (Highland Boundary Fault and Southern Uplands Fault). This was expected from the Golden Eagle Topography model, and presumed isolation was the premise for an ongoing reinforcement project in the south of Scotland, translocating eagles from the north (South Scotland Golden Eagle Project: SSGEP). Second was that larger expanses of water can be a barrier. We found that, for a northwestern archipelago (Outer Hebrides), isolated by ≥24 km of sea (and with prior assignation of genetical and historical separation), there were no tagged bird movements with the Inner Hebrides and/or the Highlands mainland (the main sub-population), confirming their characterisation as a second sub-population. Results on the willingness of eagles to cross open sea or sea lochs (fjords) elsewhere in Scotland were consistent on distance. While apparently weaker than the Outer Hebrides in terms of separation, the designation of a third sub-population in the south of Scotland seems appropriate. Our results validate the SSGEP, as we also observed no movement of birds across closer sea crossings from abundant Highland sources to the Southern Uplands. Based on telemetric results, we also identified where any re-colonisation of England, due to the SSGEP, is most likely to occur. We emphasise, nevertheless, that our study’s records during dispersal will be greater than the natal dispersal distances (NDDs), when birds settle to breed after dispersal, and NDDs are the better shorter arbiter for connectivity.

Approach Distances of Scottish Golden Eagles Aquila chrysaetos to Wind Turbines According to Blade Motion Status, Wind Speed, and Preferred Habitat

Understanding drivers underlying birds’ responses to operational wind turbines is essential for robust wind farm proposal assessments, especially for large raptors with life history traits engendering sensitivity to impacts from two potential adverse effects: fatality through collision with rotating turbine blades and functional habitat loss through avoidance of turbines. The balance between these two potential effects represents opposing extremes on a continuum and is influenced by several factors. Collisions have an obvious impact on survival, but the impacts of avoidance may be more insidious and potentially more significant for a population. It is reasonable to conclude that collisions are less likely when blades are motionless. Consequently, turbine shutdown systems (TSSs, “shutdown on demand” or “curtailment”), instigated as raptors approach operational turbines, may provide mitigation against collisions. By contrast, if avoidance is most likely, this could be independent of blade motion, and TSSs/curtailment would provide no mitigation against habitat loss. For birds tending to wariness of turbines, therefore, it is important to understand if it is conditional on blade motion. Scottish golden eagles show a strong propensity to avoid (be wary of) turbines, subject largely to the suitability of habitat at and surrounding turbine locations. A previous Scottish study found that approach distances to turbines by non-territorial eagles were unaffected by blade motion but were closer at higher wind speed. Here, we analyse movement data from a GPS-tagged territorial eagle and non-territorial eagles responding to the motion status (and wind speed) of turbines at another Scottish wind farm. Eagles’ approach distances to turbines were only weakly affected by blade motion but were closer at higher wind speed. We again found that habitat suitability in and around turbine locations was strongly influential on eagles’ approach distance to turbines. Our confirmation that blade motion had little effect on Scottish golden eagles’ wariness of turbines suggests that for eagles that are prone to avoid turbines, their wariness is a response to turbines per se, and not blades’ movement. In our study system, and others where avoidance is the predominant response, curtailment of turbines’ operation on birds’ close approaches, or making turbine blades more obvious, should, therefore, have little material influence on functional habitat loss impacts. If true, this has important implications for wind farm designs and any proposed mitigation.

Effect of implementation of irrigation on raptor and corvid populations in a Mediterranean agrosystem

We analyzed changes in the composition of the community of birds of prey and corvids in a rainfed agrosystem after the transformation of 37.2 % of the sampled area into irrigated land between 2005 and 2020. We sampled 57 transects (372 km per year) and fitted generalized linear mixed models (GLMM) to study changes in species occurrence. Our results showed that specific richness and the Shannon index did not vary significantly between rainfed and irrigated transects, but there was a certain positive trend when comparing the years 2005 and 2020. Regarding the differences detected for each species, the occurrence of Montagu’s harrier Circus pygargus, hen harrier Circus cyaneus, Eurasian short-toed eagle Circaetus gallicus, griffon vulture Gyps fulvus and carrion crow Corvus corone was significantly lower in irrigated land than in rainfed land, while magpie Pica pica, Western marsh harrier Circus aeruginosus, common kestrel Falco tinnunculus and black kite Milvus migrans showed a significantly higher occurrence in the irrigated transects. In addition, our findings confirm a significant decrease in occurrence between 2005 and 2020 both in rainfed and irrigated areas for Montagu’s harrier, hen harrier and magpie, while Western marsh harrier, golden eagle Aquila chrysaetos, common buzzard Buteo buteo, red kite Milvus milvus, griffon vulture Gyps fulvus, red-billed chough Pyrrhocorax pyrrhocorax and Western jackdaw Coloeus monedula were detected significantly more frequently in 2020 than in 2005. These results suggest that assessment of the impact of a new irrigation system should focus on the most characteristic species of rainfed agrosystems because the apparently positive effect on other species, equally protected but more generalist, may mask the real effect on conservation.

Characteristics of cliff nest sites of Golden Eagles in forested hills of southeast Norway

Cover photo: Adult Golden Eagle. Photo: Kristian Henriksen. The characteristics of cliff nest sites of the Golden Eagle Aquila chrysaetos were evaluated from a sample of 57 nests, located during 2000–2020 in the forested valley of Valdres in southeast Norway. About 80% of nests were facing to the south and east, but availability of nest ledges seemed largely a consequence of cliff structure and orientation. Among the 57 nest sites, 4% were placed in a corner with vertical walls, 33% on a ledge with overhang, 10% on a ledge with a vertical back wall, 2% on a ledge with a reclining wall, 49% within a cavity and 2% within a cave. Thus, about 83% of the nest sites were sheltered by an overhang, a cavity or a cave in the cliff within 0.5–2 meters from the nest, and only 16% of sites lacked shelter from above. Heavy snowfall in early spring, torrential rain or strong winds in spring and summer may increase mortality among the nestlings unless the nest site is well sheltered. Moreover, a dry and snowless nest may allow the eagles to start early incubation in late March, thereby increasing fledgling survival. Cavitynests are sheltered sites with less visibility that might protect from attacks from other raptors and Ravens Corax corax.

Substantial Variation in Prospecting Behaviour of Young Golden Eagles Aquila chrysaetos Defies Expectations from Potential Predictors

Natal dispersal of large raptors is poorly understood, despite being a crucial transitional life-cycle phase affecting gene flow and population dynamics. A research-gap rarely examined concerns how young dispersing raptors strategize movements towards first settlement on a prospective breeding territory. First territory settlement is a critical decision for a lifetime and can take several years. With such importance, large raptors should theoretically devote considerable effort to acquire accurate information during prospection. Nevertheless, when discovery of territorial opportunities may be difficult, but easier in vacant territories, we posit two extremes in strategizing prospection behaviours: (1) “Quick, grab it when available with limited reconnaissance,” as opposed to (2) “Slow, waiting game with frequent reconnaissance”. We analysed pre-settlement data from 37 GPS-tagged nestling golden eagles, later recorded as having settled on their first territory. The number of eagles’ unique daily visits to their later settled territories was a measure of prospection intensity. We documented substantial variation in prior visits, between less than 10 to several hundred. Analyses considered several potential predictors. We expected a positive association between number of prospecting visits and natal dispersal duration, since with more time to gather information there should be more visits. We also expected fewer prospecting visits in prior vacant territories. Neither of these expectations were supported. There was a non-significant tendency for more prospection visits by males. Our study provides novel information on a seldom-studied behaviour in a large raptor. It illustrates substantial variation in prospecting behaviour, but expectations of potential drivers behind this variation were not confirmed, urging further study.

Suri orao Aquila Chrysaetos (Linnaeus, 1758) na prostoru zapadne i jugozapadne Srbije - veličina populacije, gnezdeća ekologija i faktori ugrožavanja

This article presents the long-term study results on the golden eagle Aquila chrysaetos (Linnaeus, 1758) breeding population in the hilly and mountainous landscapes of western and southwestern Serbia, which were obtained during 11 consecutive re-productive seasons (2011-2021). Primarily, the study examines parameters such as population size, density, nesting ecology, and threats. Data on the mentioned parameters were collected during extensive fieldwork and analyzed using appropriate statistical methods. The summarised results bring valuable insights into hypotheses and questions concerning the golden eagle breeding ecology in western and southwestern Serbia. In addition, the presented research provides a solid starting point for further studies of the monitored population and the possibility of expanding monitoring to the neighbouring areas of the central Balkans.

Population dynamics of recovering apex predators: Golden eagles in a Mediterranean landscape

AbstractApex predators play a critical role in shaping the biological and functional diversity of ecosystems. Like in many other living groups, population dynamics of apex predators exhibit auto‐regulation traits, including density‐dependent processes, which can be important for limiting population numbers. However, the study of these processes is challenging due to their slow life history traits, especially when their populations are depressed. Our main objective is to describe mechanisms driving population dynamics in apex predators by documenting the relationship between population density and demographic parameters at population level and analyzing the influence of population density and other environmental factors on the reproductive parameters at territory level. We used as biological model a recovering population of golden eagles Aquila chrysaetos in a Mediterranean landscape (North Spain). We monitored yearly all known eagle pairs within the study area for 28 years, implying 1539 reproductive events in a total of 84 territories. The average density was 3.04 pairs/1000 km2, and the reproductive success, productivity, and flight rates averaged 0.45, 0.54, and 1.20, respectively. The population increased during the study period (from 37 to 78 pairs), although we did not find any effect of density on the reproductive parameters at population level. At territory level, we found that size of territory, proportion of open habitat, and spring precipitation increased reproductive performance, while older territories performed worse than new ones. Our findings suggest that population dynamics in recovering apex‐predators are driven by a complex combination of compensatory density‐dependent processes, mainly operating at territorial level, and by environmental factors mainly related with resource availability and human pressure. For species with slow life history traits, population recovery seems to be facilitated by re‐colonization from refuge areas, wilder but less productive, to areas with higher resource availability, once they became safer after reduction of human pressures.

Problems Applying a Model for Red-Tailed Hawks and American Crows to Golden Eagles

In the 13(1) issue of the Journal of Fish and Wildlife Management , Dwyer and Mojica (2022) tested the usefulness of a 2014 model, based on Southern California Edison (SCE) data, for assessing avian electrocution risk of power poles to predict electrocution risk for golden eagles Aquila chrysaetos (Dwyer et al. 2014). They suggested that if the 2014 model is applicable to golden eagles, it could be used by the U.S. Fish and Wildlife Service (USFWS) when determining appropriate compensatory mitigation for incidental take permits issued under the Bald and Golden Eagle Protection Act. Power pole retrofits currently serve as mitigation for several types of golden eagle take permits including but not limited to wind energy facilities, mining construction and operators, electric utility operators, and nest disturbance.

Establishing haematological and biochemical reference intervals for free-ranging Scottish golden eagle nestlings (Aquila chrysaetos)

Health assessment of individuals is an important aspect of monitoring endangered wildlife populations. Haematological and biochemical values are a common health assessment tool, and whilst reference values are well established for domestic species, they are often not available for wild animal species. This study established 31 haematological and biochemical reference intervals for golden eagle (Aquila chrysaetos) nestlings in Scotland, in order to improve the understanding of the species’ health and support conservation efforts. Reference intervals were created from 47 nestlings (ages 2–7.5 weeks old) across 37 nests, to date, the largest sample of wild individuals of this species and age cohort sampled for these purposes. Upper reference intervals for concentrations of lymphocytes, total protein, cholesterol, triglycerides, uric acid, and monocytes, calculated in this study, are higher than those found for adult raptors and the interval span is higher than that observed in adult raptors for concentrations of AST, albumin, eosinophil, LDH, and monocyte count. Statistically significant positive correlations were found with age and concentrations of haemoglobin, lymphocytes, serum pH, and creatine kinase, and significant negative correlations with age for concentrations of thrombocytes, heterophils, total protein, globulin, and lactate dehydrogenase. Packed cell volume was significantly higher for females than males, and concentration of calcium and eosinophils were higher for individuals in good body condition than those in moderate body condition. The reference intervals produced by this study will be of important use to the veterinary and conservation management communities and will aid the long-term monitoring of the Scottish golden eagle population health.

Exploring golden eagle habitat preference using lidar-based canopy bulk density

ABSTRACT A lidar-derived canopy height profile (CHP), generated from canopy bulk density (CBD) estimates for a sequence of 1-m increments through the canopy, provides a physical measure of forest structure. Measurement of physical properties are intuitively understandable and thus facilitate the use of lidar for investigating hypotheses regarding avian resource use. We illustrate the use of lidar-derived physical measures to explore the hypothesis that golden eagles (Aquila chrysaetos) prefer an open understory, which potentially aids visual identification of prey. Two golden eagles fitted with GPS tracking devices overwintered in the New Jersey Pinelands National Preserve. We generated CHPs from discrete-return lidar data for an area occupied by the birds. We compared the CHPs of sites the birds occupied to the surrounding available habitat and found that the occupied sites were significantly lower in CBD from the ground up to 5 m for perched/stationary birds, and from the ground up to 8 m for birds in flight. These results could be used by forest resource managers for promoting golden eagle habitat through prescribed fire. In addition, these results demonstrate the power of lidar to generate physically and intuitively meaningful measures of forest structure.

Demographic partitioning of dynamic energy subsidies revealed with an Ornstein-Uhlenbeck space use model.

In populations across many taxa, a large fraction of sexually mature individuals do not breed but are attempting to enter the breeding population. Such individuals, often referred to as "floaters," can play critical roles in the dynamics and stability of these populations and buffer them through periods of high adult mortality. Floaters are difficult to study, however, so we lack data needed to understand their roles in the population ecology and conservation status of many species. Here, we analyzed satellite telemetry data with a newly developed mechanistic space use model based on an Ornstein-Uhlenbeck process to help overcome the paucity of data in studying the differential habitat selection and space use of floater and territorial golden eagles Aquila chrysaetos. Our sample consisted of 49 individuals tracked over complete breeding seasons across 4 years, totaling 104 eagle breeding seasons. Modeling these data mechanistically was required to disentangle key differences in movement and particularly to separate aspects of movement driven by resource selection from those driven by use of a central place. We found that floaters generally had more expansive space use patterns and larger home ranges, as well as evidence that they partition space with territorial individuals seemingly on fine scales through differential habitat and resource selection. Floater and territorial eagle home ranges overlapped markedly, suggesting that floaters use the interstices between territories. Furthermore, floater and territorial eagles differed in how they selected for uplift variables, key components of soaring birds' energy landscape, with territorial eagles apparently better able to find and use thermal uplift. We also found relatively low individual heterogeneity in resource selection, especially among territorial individuals, suggesting a narrow realized niche for breeding individuals, which varied from the level of among-individual variation present during migration. This work furthers our understanding of floaters' potential roles in the population ecology of territorial species and suggests that conserving landscapes occupied by territorial eagles also protects floaters.

Age of First Territory Settlement of Golden Eagles Aquila chrysaetos in a Variable Competitive Landscape

With life-history traits involving high survival, low reproductive output, years of natal dispersal and deferred maturity, the population ecology and behaviour of large raptors which occur at low densities can be difficult to study. The age at which large raptors first settle on a prospective breeding territory receives relatively little attention, but is a key metric in population modelling including, for example, projections of reintroduction projects. It can also be a barometer of the “health” of populations and the availability of breeding opportunities. The advancement of GPS-telemetry has proved invaluable in gaining insights into several aspects of large raptor ecology and behaviour. Age of first territory settlement (AFTS) is one such aspect. AFTS is important in modelling population trajectories and considering individuals’ lifetime reproductive success. We used an algorithm based on GPS-records from dispersing Golden Eagles tagged as nestlings in Scotland to estimate AFTS. While the lifespan of GPS-tags can bias against settlement dates of older birds, they can also potentially reveal settlement ages difficult or impossible to discern from other methods. We found a range of ages for AFTS, including those in their second calendar year; much younger than previously documented by other methods. Ground-truthing – when possible and if inevitably slightly delayed – confirmed territory occupation on field-based survey criteria. We found that eagles settled younger in vacant territories and when older in occupied existing territories. Birds’ sex had no effect on AFTS. Birds which dispersed earlier from their natal territory (indicative of “quality” from some previous research) had no association with AFTS. Our results indicate that within technological temporal limits GPS-data can provide for accurate and precise estimations of AFTS including early settlement not consistently or precisely recorded by other methods. Within our study’s variable competitive landscape we found that AFTS was associated with the availability of territorial opportunities but not with the timing of dispersal. These findings have consequences for studying and understanding large raptor population dynamics.

Seasonal variation in resource selection by subadult golden eagles in the Great Basin Desert

Golden eagles Aquila chrysaetos are a long‐lived and wide‐ranging species believed to be stable or in slight decline across North America. Golden eagles have an extended subadult stage (4–5 years) that is critical to maintaining recruitment into the breeding population and population viability. Compared to adult golden eagles, the ecology of subadult golden eagles (hereafter, subadults) has received little attention. We investigated patterns of resource selection for subadults in the Great Basin Desert of the western United States during summer and winter, 2013–2019. We monitored 46 subadults with GPS transmitters and related locations (n = 99 037) with predictors hypothesized to influence seasonal patterns of space use with mixed‐effects logistic regression. Subadults selected for ridges and upper slopes in summer and winter, but higher elevations in summer. Subadults showed weak selection for lower ridge density in summer, which was likely facilitated by selection for areas with greater thermal wind current potential. In contrast, subadults showed strong selection for higher ridge density in winter. Subadults selected areas further from roads in summer and closer to roads and electrical transmission lines in winter, which may be related to winter scavenging of road‐killed ungulates. Resource selection functions suggested subadults selected for shrublands and woodlands in both seasons, but odds ratios revealed that during winter subadults avoided shrublands and increased selection of woodlands relative to summer. Subadults selected for areas with infrequent fires in both seasons; areas with frequent fires were avoided in summer but selected for in winter. Seasonal changes in resource selection suggested that subadults used woodlands more than expected, potentially reflecting spatial partitioning by subadults to lower‐quality habitats to minimize competition with breeding adults during winter when energetic demands for thermoregulation were presumably higher and prey more limited.

Importance of Power Pole Selection When Retrofitting for Eagle Compensatory Mitigation

AbstractIn the United States, the bald eagle Haliaeetus leucocephalus and golden eagle Aquila chrysaetos are managed by the U.S. Fish and Wildlife Service to ensure the species are stable or increasing while allowing for potentially negative effects from anthropogenic sources. Compensatory mitigation, through retrofitting high-risk power poles to reduce electrocutions, can be used to offset negative effects, enabling the U.S. Fish and Wildlife Service to achieve their management objectives of species stability and persistence. Regulators, permit holders, electric utilities, and consultants lack an objective and repeatable method for discriminating between high-risk and low-risk power poles. To illustrate the importance of accurately identifying and retrofitting high-risk poles, we compare conservation benefits among three retrofitting project scenarios: 1) high-risk poles only, 2) a circuit of both low- and high-risk poles, and 3) low-risk poles only. We assert that, in the absence of a common definition of high-risk power poles applied uniformly across the landscape, mitigation approved by the U.S. Fish and Wildlife Service could fall short of its intended value and be unable to meet management objectives. We define high-risk poles in the context of compensatory mitigation as poles in high-quality bald or golden eagle habitat with a relative risk index ≥ 0.40 based on number of phases, number of jumper wires, and presence of pole grounding. We estimate that the conservation benefit of retrofitting a high-risk pole is at least 5.25 times greater than the benefit of retrofitting a low-risk pole. In the long-term, if compensatory mitigation intended to achieve management objectives falls short of its assumed conservation value, the U.S. Fish and Wildlife Service could be forced to limit future permit authorizations until bald or golden eagles can recover from incorrectly calculated conservation benefits. To avoid that negative outcome, we recommend that the U.S. Fish and Wildlife Service set consistent and transparent standards for identifying poles to count as compensatory mitigation credit using our proposed definition of a high-risk power pole.

Can an Avian Electrocution Risk Model From California Guide Retrofitting Throughout the Western United States?

Abstract A previously published model of avian electrocution risk, the “2014 model,” compared power poles that electrocuted birds (electrocution poles; including 21 golden eagle Aquila chrysaetos electrocutions) with poles not known to have electrocuted birds (comparison poles). The 2014 model produces pole-specific risk index scores between 0 and 1. The scores rank relative risk so electric utilities can maximize conservation benefits per dollar spent by focusing retrofitting on poles with greatest risk. Although the creation of the 2014 model encompassed a study population of birds and poles in southern California, the 2014 model has potential for use in managing a target population of raptors including golden eagles throughout the western United States. Use beyond southern California is only appropriate if the study population is similar enough to the target population for the 2014 model to predict risk effectively. To evaluate similarity, we examined five sources of evidence: 1) the relative consistency in electrical safety codes for power poles; 2) the body sizes of golden eagles in the study and target populations; and consistency in structure-specific factors associated with 3) golden eagle electrocutions in other studies, 4) other avian electrocutions, and 5) previously unreported golden eagle electrocutions. We found that although the study population in the 2014 model included relatively few golden eagles, data were sufficient to create a model that is applicable to a target population throughout the western United States. The model also can be useful in helping determine equivalencies between pole types if utilities seek to compare benefits of retrofitting small numbers of high-risk poles with large numbers of low-risk poles.

Resource selection functions based on hierarchical generalized additive models provide new insights into individual animal variation and species distributions

Habitat selection studies are designed to generate predictions of species distributions or inference regarding general habitat associations and individual variation in habitat use. Such studies frequently involve either individually indexed locations gathered across limited spatial extents and analyzed using resource selection functions (RSFs) or spatially extensive locational data without individual resolution typically analyzed using species distribution models. Both analytical methodologies have certain desirable features, but analyses that combine individual‐ and population‐level inference with flexible non‐linear functions may provide improved predictions while accounting for individual variation. Here, we describe how RSFs can be fit using hierarchical generalized additive models (HGAMs) using widely available software, providing a means to explore individual variation in habitat associations and to generate species distribution maps. We used GPS tracking data from golden eagles Aquila chrysaetos from across eastern North America with four environmental predictors to generate monthly distribution models. We considered three model structures that assumed different amounts of individual variation in the functional relationship between predictors and habitat use and used k‐fold cross‐validation to compare model performance. Models accounting for individual variability in shape and smoothness of functional responses performed best. Eagles exhibited the least amount of individual variation in response to land cover variables during winter months, with most individuals more closely adhering to the population‐level trend. During the summer months, eagles exhibited more substantial individual variation in shape and smoothness of the functional relationships, suggesting some need to account for individual variation in eagle habitat use for both inferential and predictive purposes, during this time of year. Because they allow users to blend flexible functions with random effects structures and are well‐supported by a variety of software platforms, we believe that HGAMs provide a useful addition to the suite of analyses used for modeling habitat associations or predicting species distributions.

Non-territorial GPS-tagged golden eagles Aquila chrysaetos at two Scottish wind farms: Avoidance influenced by preferred habitat distribution, wind speed and blade motion status.

Wind farms can 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. These effects may not be mutually exclusive. Using detailed data from 99 turbines at two wind farms in central Scotland and thousands of GPS-telemetry data from dispersing golden eagles, we tested three hypotheses. Before-and-after-operation analyses supported the hypothesis of avoidance: displacement was reduced at turbine locations in more preferred habitat and with more preferred habitat nearby. After-operation analyses (i.e. from the period when turbines were operational) showed that at higher wind speeds and in highly preferred habitat eagles were less wary of turbines with motionless blades: rejecting our second hypothesis. Our third hypothesis was supported, since at higher wind speeds eagles flew closer to operational turbines; especially–once more–turbines in more preferred habitat. After operation, eagles effectively abandoned inner turbine locations, and flight line records close to rotor blades were rare. While our study indicated that whole-wind farm functional habitat loss through avoidance was the substantial adverse impact, we make recommendations on future wind farm design to minimise collision risk further. These largely entail developers avoiding outer turbine locations which are in and surrounded by swathes of preferred habitat. Our study illustrates the insights which detailed case studies of large raptors at wind farms can bring and emphasises that the balance between avoidance and collision can have several influences.

Golden Eagle dietary shifts following wildfire and shrub loss have negative consequences for nestling survivorship

Abstract Wildfires and invasive species have caused widespread changes in western North America’s shrub-steppe landscapes. The bottom–up consequences of degraded shrublands on predator ecology and demography remain poorly understood. We used a before–after paired design to study whether Golden Eagle (Aquila chrysaetos) diet and nestling survivorship changed following wildfires in southwestern Idaho, USA. We assessed burn extents from 1981 to 2013 and vegetation changes between 1979 (pre-burn) and 2014 (post-burn) within 3 km of Golden Eagle nesting centroids. We measured the frequency and biomass of individual prey, calculated diet diversity indexes, and monitored nestling survivorship at 15 territories in 1971–1981 and 2014–2015. On average, 0.70 of the area within 3 km of nesting centroids burned between 1981 and 2013, and the mean proportion of unburned shrubland decreased from 0.73 in 1979 to 0.22 in 2014. Diets in post-burn years were more diverse and had a lower proportion of some shrub-associated species, such as black-tailed jackrabbits (Lepus californicus) and mountain cottontails (Sylvilagus nuttallii), and a higher proportion of American Coots (Fulica americana), Mallards (Anas platyrhynchos), Piute ground squirrels (Urocitellus mollis), and Rock Pigeons (Columba livia) compared with pre-burn years. A high proportion of waterfowl represented a novel change in Golden Eagle diets, which are typically dominated by mammalian prey. Nestling survivorship was positively associated with the proportion of black-tailed jackrabbits and negatively associated with the proportion of Rock Pigeons in eagle diets. Rock Pigeons are a vector for Trichomonas gallinae, a disease-causing protozoan lethal to young eagles. Nesting attempts were more likely to fail (all young die) in the post-burn period compared with the pre-burn period. Dietary shifts are a common mechanism for predators to cope with landscape change, but shifts away from preferred prey to disease vectors affect nestling survivorship and could lead to population-level effects on productivity.

Responses of dispersing GPS‐tagged Golden Eagles (Aquila chrysaetos) to multiple wind farms across Scotland

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 < 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.