Golden Eagles Aquila Chrysaetos Research Articles

Ecosystem processes, land cover, climate, and human settlement shape dynamic distributions for golden eagle across the western US

AbstractSpecies–environment relationships for highly mobile species outside of the breeding season are often highly dynamic in response to the collective effects of ever‐changing climatic conditions, food resources, and anthropogenic disturbance. Capturing dynamic space‐use patterns in a model‐based framework is critical as model inference often drives place‐based conservation planning. We applied dynamic occupancy models to broad‐scale golden eagle Aquila chrysaetos survey data collected annually from 2006 to 2012 during the late summer post‐fledging period in the western US. We defined survey sites as 10 km transect segments with a 1 km buffer on either transect side (n = 3540). Derived estimates of occupancy were low (4.4–7.9%) and turnover rates – the probability that occupied sites were newly occupied – were high (88–94%), demonstrating that annual transiency in occupancy dominates late summer behavior for golden eagles. Despite low philopatry during late summer, variation in golden eagle occupancy could be explained by a suite of land cover and annual‐varying covariates including gross primary productivity, drought severity, and human disturbance. Our summary of 13 years of predicted occupancy by golden eagles across the western United States identified areas that are consistently used and that may contribute significantly to golden eagle conservation. Restricting development and targeting mitigation efforts in these areas offers practitioners a framework for conservation prioritization.

A simple topographical model to predict Golden Eagle Aquila chrysaetos space use during dispersal

Many large raptors exploit or rely on anabatic and orographic winds which provide vertical lift, to supplement or provide the energy fuelling flight. Airspace is therefore a critical habitat for such large raptors and its use is subject to the underlying terrestrial topography, because particular topographical features are more likely to provide wind‐energetic lift. Accordingly, ridges and/or ‘rugged topography’ are common preferred features in habitat use by large raptors. Our study aimed to provide a simple model of space use for a large raptor, the Golden Eagle Aquila chrysaetos, based on thousands of GPS telemetry records during juvenile dispersal of 92 birds tagged as nestlings between 2007 and 2016 across upland Scotland. Model development was based on the hypothesis that four topographical variables would be influential: slope, aspect, altitude and distance from ridge. The telemetry dataset was divided into training and two testing components. The first testing set was derived by a temporal split resulting in approximately equal sample size on records and some temporal overlap in individuals’ records with training data. The second testing set involved no individuals from the training set. Aspect was removed early in training model development because it was not influential. The model found that young Golden Eagles preferred, or used according to availability, space above slopes greater than 10°, at an altitude of ≥ 300 m, and within 300 m of a ridge. The test data were highly correlated with those from the training data in the model variables, and performance as regard to expected preferences from the model was improved in both test datasets, indicating the model was robust. Given the apparent universal nature of large raptor dependence on topography, that topography is relatively immutable according to time and use, and that topographical data are readily available, we commend our approach to other habitat preference studies of Golden Eagles and other large raptors elsewhere.

Observations on the roosting behaviour of adult male Golden Eagles from satellite telemetry

ABSTRACT The roosting behaviour of two adult male Golden Eagles Aquila chrysaetos was studied using GPS satellite tags. One eagle (tag 816) used 120 different roost sites over two years and the other (tag 991) more than 87 roosts over one year. These numbers of roost sites were substantially greater than expected from previous field-based studies. Around 70% of the roost sites were used on only one night and such roosts accounted for 17–25% of roosting behaviour. Seven roosts that were used for more than ten nights each (multi-use roosts) were located for one bird and five for the other. Roosts that were used on only one night tended to be used more than expected on evenings when winds were light (<5 ms-1), while multi-use roosts were used more than expected on evenings with strong winds (>10 ms-1). Hence, eagles appear to select more-sheltered, multi-use roost sites during strong winds.

Natal Dispersal Distance of Golden Eagles in the Southwestern United States

Abstract Data on natal dispersal distances (NDDs) of golden eagle Aquila chrysaetos in North America are needed to define local area populations and inform decisions authorizing take (i.e., injury, death, or disturbance) of the species via federal permit. Sixteen golden eagles (6 males, 10 females) tagged with satellite transmitters as ∼8-wk-old nestlings in the southwestern United States during 2010–2013 dispersed a mean of 55.3 km (SD = 29.7, median = 64.5), either 1) between their natal nest sites and nests where they first bred (n = 3 females, all subadults, i.e., in their fourth year of life), or 2) between natal sites and where they permanently settled as adults at least in their fifth year of life, but did not necessarily breed (i.e., exhibiting only gross natal dispersal). On average, females dispersed about 50% farther than males; mean NDD of males and females was 41.2 km (90% credible interval = 11.1–75.2) and 63.8 km (44.8–82.6), respectively. Median NDD of males and females was 41.5 and 65.8 km, respectively; in a Bayesian framework, the estimated difference in posterior median distributions of male and female NDDs was 22.2 km (−15.7 to 57.3; P ≠ 0 = 0.89), tentatively indicating that NDD of golden eagles in our study area may be female biased. Although our findings are based on a relatively small data set including both effective and gross natal dispersal records, they represent the first comparison of NDD between sexes of golden eagle in North America and the first published records on the continent of the species' NDD based on telemetry methods. More work is needed to validate whether golden eagle NDD in at least some regions of North America is female biased, which could have important implications for authorizing take of the species.

Acute and Chronic Lead Exposure in Four Avian Scavenger Species in Switzerland.

Despite irrefutable evidence of its negative impact on animal behaviour and physiology, lethal and sublethal lead poisoning of wildlife is still persistent and widespread. For scavenging birds, ingestion of ammunition, or fragments thereof, is the major exposure route. In this study, we examined the occurrence of lead in four avian scavengers of Switzerland and how it differs between species, regions, and age of the bird. We measured lead concentration in liver and bone of the two main alpine avian scavengers (golden eagle Aquila chrysaetos and bearded vulture Gypaetus barbatus) over the entire area of the Swiss Alps and two of the main avian scavengers occurring in the lowlands of Switzerland (red kite Milvus milvus and common raven Corvus corax). Of those four species, only the bearded vulture is an obligate scavenger. We found that lead burdens in the two alpine avian scavengers were higher than those found for the same species elsewhere in Europe or North America and reached levels compatible with acute poisoning, whereas lead burdens of the two lowland avian scavengers seemed to be lower. Several golden eagles, but only one red kite with abnormally high bone lead concentrations were found. In all four species, a substantial proportion of birds had elevated levels which presumably represent recent (liver lead levels) or past (bone lead levels) uptake of sublethal doses of lead.

Solar and terrestrial radiations explain continental-scale variation in bird pigmentation.

Animals living on the earth's surface are protected from the damaging effects of solar ultraviolet (UV) radiation by melanin pigments that color their integument. UV levels that reach the earth's surface vary spatially, but the role of UV exposure in shaping clinal variations in animal pigmentation has never been tested. Here, we show at a continental scale in Europe that golden eagles Aquila chrysaetos reared in territories with a high solar UV-B radiation exposure deposit lower amounts of the sulphurated form of melanin (pheomelanin) in feathers and consequently develop darker plumage phenotypes than eagles from territories with lower radiation exposure. This clinal variation in pigmentation is also explained by terrestrial γ radiation levels in the rearing territories by a similar effect on the pheomelanin content of feathers, unveiling natural radioactivity as a previously unsuspected factor shaping animal pigmentation. These findings show for the first time the potential of solar and terrestrial radiations to explain pigmentation phenotype diversity in animals, including humans, at large spatial scales.

Monitoring methods for the Golden Eagle Aquila chrysaetos in Norway

ABSTRACTCapsule: A description of the methods used for monitoring the Golden Eagle Aquila chrysaetos in NorwayAims: To provide a comprehensive description of monitoring methods.Methods: The intensive monitoring of the Golden Eagle in Norway started in 1991 as part of a national monitoring programme initiated by the Directorate for Nature Management (now the Norwegian Environment Agency). It has since become part of the Norwegian Large Predator Programme, and Golden Eagles are currently being monitored in 12 separate areas. Here we provide a comprehensive description of the current methods used in the intensive monitoring, with definitions, fieldwork and evaluation criteria for the final breeding status. In addition, a description of estimation of annual adult survival by genetic analysis is given. We describe the current methodology used in the intensive part of the Golden Eagle monitoring in Norway.Results: We present some results derived from the Norwegian monitoring system and discuss the potential for further analyses. In addition, we highlight aspects in the monitoring of the Golden Eagles where our methods deviate slightly from those applied in other countries and the potential effects of these.Conclusions: Intensive long-term monitoring programmes, such as this, will become increasingly valuable for monitoring the impact of environmental change, both from natural phenomena and from anthropogenic activities. To facilitate comparisons among the Golden Eagle monitoring programmes, detailed knowledge about the various methods applied is important.

Acute intraparenchymal cerebral haemorrhage in an Iberian golden eagle \u2013 a case report

BackgroundIn birds there are reports of intracranial lesions but not of the clinical, computed tomographic and histopathologic features of acute intraparenchymal cerebral haemorrhage in Iberian golden eagle.Case presentationThe following report describes a case of a 30-year-old Iberian golden eagle (Aquila chrysaetos homeyeri) with no history of trauma, presented with acute opisthotonus, left head tilt and circling, anisocoria, positional nystagmus, and ataxia. The main differential diagnosis were hypovitaminosis B or E and intracranial disease due to trauma, infection, toxins or masses. A computed tomography (CT) of the head was performed with an 8-slices scanner and evidenced a hyperdense (63–65 HU) non-enhancing homogeneous well delineated round area in the midbrain, with 6 mm in its highest diameter. The attenuation values and the non-enhancing nature of the lesion strongly suggested the diagnosis of acute intraparenchymal haemorrhage, which was histologically confirmed after necropsy.ConclusionsIn birds with a central neurological dysfunction, the diagnosis of acute brain haemorrhage should be considered when the CT evidences a non-enhancing, homogeneous, well circumscribed hyperattenuated round area.

Origins of lead in populations of raptors

AbstractAlthough poisoning from anthropogenically derived lead threatens wildlife of many species, routes of lead exposure are unclear and rarely empirically tested. We used blood lead concentration and isotope ratio (207Pb/206Pb) data from populations of four species of raptors from across North America to test hypotheses associated with lead exposure via inhalation versus ingestion. Mean variation in blood lead concentration among cohort siblings was non‐zero at nests of ferruginous hawks Buteo regalis and osprey Pandion haliaetus (P &lt; 0.001 and P &lt; 0.001), indicating exposure via episodic ingestion. However, within‐nest variation in blood lead concentration was not significantly different from zero among cohort siblings at nests of bald eagles Haliaeetus leucocephalus and golden eagles Aquila chrysaetos (P = 0.014 and P = 0.023), consistent with exposure via continuous inhalation. Isotope ratio data corroborated the lead concentration data and within‐nest average and variance of blood lead concentrations were positively correlated (r = 0.70 to 0.94), indicating episodic ingestion. This study provides some of the first empirical population‐level data to evaluate mechanisms of lead exposure and demonstrates the importance of lead ingestion to avian predators and scavengers.

Rehabilitation of an Injured Golden Eagle (Aquila Chrysaetos): A Case Study

Rehabilitation of an Injured Golden Eagle (Aquila Chrysaetos): A Case Study

Status of Golden Eagle Aquila chrysaetos in Britain in 2015

ABSTRACTCapsule: A complete survey of Golden Eagles Aquila chrysaetos in Britain in 2015 found that the population had increased by 15% since 2003 to 508 territorial pairs.Aims: The survey aimed to investigate the population size, distribution and breeding success of Golden Eagles in Britain, and to compare results with similar surveys since the early 1980s.Methods: Every home range was visited on a minimum of three occasions between January and August 2015. First, to look for eagles or signs of their presence (January–March), then to look for evidence of breeding or further checks for occupation (April–June) and finally to record productivity of nesting pairs (July–August).Results: The figure of 508 territorial pairs represents a 15% increase in the population from 442 pairs in 2003. The proportion of home ranges occupied was 70%. The largest increases in the proportion of occupied home ranges were in south-central Highlands (71%), northern moors and flows (38%) and northwest Highlands (29%), with modest increases of up to 10% in the other regions. Productivity was lower in 2015 than in 2003, and there was significant variation in breeding success between regions.Conclusion: The British Golden Eagle population has increased since 2003, although the species is absent from England and Wales. The population now meets the abundance target identified to define favourable conservation status in Scotland, and while home range occupancy has increased there is regional variation, with some regions falling below the target levels. A combination of increased annual monitoring and tagging of eagles, as well as the introduction of new legislation, may serve as effective deterrents against persecution of eagles thus facilitating this population increase. However, concerns remain over low levels of home range occupancy particularly in the east Highlands, but also the proportion of sub-adult pairs holding territory in that region and in the south-central Highlands. Persecution associated with grouse moor management has been highlighted as a particular population constraint in both of these areas.

Identifying Bald Versus Golden Eagle Bones: A Primer for Wildlife Biologists and Law Enforcement Officers

Abstract Remains of bald eagles Haliaeetus leucocephalus and golden eagles Aquila chrysaetos are regularly encountered in avian mortality surveys and wildlife crime investigations. These species exhibit well-documented plumage differences, allowing identification in most instances when feathers are present. However, skeletal remains are much more difficult to identify and may be the only material available after mortality events (e.g., decomposed remains associated with power lines or wind turbines). Eagle bones are also sometimes incorporated into crafted items without other associated remains. I describe and illustrate shape-based osteological characters that have been determined to be reliable for distinguishing most major bones of bald versus golden eagles. Using the annotated photographs provided as a guide, nonspecialists will be able to identify eagle skeletal remains with high accuracy. This information will be of interest to wildlife law enforcement officers; state, federal, and tribal wildlife biologists documenting avian mortality; and anthropologists and archaeologists.

Diet and Breeding Performance of the Golden EagleAquila Chrysaetosat the Eastern and Western Extremities of the Pyrenees: an Example of Intra-Population Variability

Summary. Diet and breeding performance show variations across species' range and between different habitats. In the present paper, we report data on the diet and breeding performance of Golden Eagles Aquila chrysaetos monitored during a ten-year period in two semi-natural landscapes located at the eastern and western extremities of the Pyrenees mountain range. In the Mediterranean area of the Corbieres, the diet was dominated by the Rabbit Oryctolagus cuniculus (31.5% of the prey items). In the Atlantic area of the Basque Country, the diet was more diverse, with the highest proportion of intra-guild predation and the highest diet breadth ever recorded for the species (Levins index of diet breadth: 12.14 vs 6.81 in the Corbieres). The proportion of successful breeding attempts was significantly higher in the Corbieres (60%) than in the Basque Country (38.5%). The same was true for mean productivity, with 0.70 and 0.45 fledglings per territory and year, respectively. These differences were partly related to...

The energy landscape predicts flight height and wind turbine collision hazard in three species of large soaring raptor

Summary Collisions of large soaring raptors with wind turbines and other infrastructures represent a growing conservation concern. We describe a way to leverage knowledge about raptor soaring behaviour to forecast the probability that raptors fly in the rotor‐swept zone. Soaring raptors are theoretically expected to select energy sources (uplift) optimally, making their flight height dependent on uplift conditions. This approach can be used to forecast collision hazard when planning or operating wind farms. Empirical investigations of the factors influencing flight height have, however, so far been hindered by observation error. We propose a two‐pronged approach. First, we fitted state‐space models to z‐axis GPS tracking data to filter heavy‐tailed observation error and estimate the relationship between vertical movement parameters and weather variables describing the energy landscape (thermal and orographic uplift potential). Second, we fitted a mechanistic model of flight height above ground based on aerodynamics and resource selection theories. The approach was replicated for five GPS‐tracked Andean condors Vultur gryphus, eight griffon vultures Gyps fulvus, and six golden eagles Aquila chrysaetos. In all individuals, movement parameters correlated with thermal uplift potential in the expected direction. In all species, collision hazard was lowest for high thermal uplift potential values. Species specificities in the presence of a peak in collision hazard for medium values of thermal uplift potential could be explained by differences in wing loading and aspect ratio. Synthesis and applications. Our fitted models convert weather data (thermal uplift potential) into a prediction of collision hazard (probability to fly in the rotor‐swept zone), making it possible to prioritize different wind development projects with respect to the relative hazard they would pose to raptors. However, our model should be combined with post‐construction monitoring to document, and eventually account for turbine avoidance behaviours in collision rate predictions.

Experimental evidence that a large raptor can detect and replace heavily damaged flight feathers long before their scheduled moult dates

Because many species of large birds must remain capable of flight during moult and breeding, complete replacement of all flight feathers often takes two or more years, with the result that their plumage normally includes many faded, worn and sometimes even broken feathers. It seems adaptive for such birds to have the ability to quickly replace severely damaged feathers. In search of such a feather replacement mechanism, we cut rectrices on a captive Golden Eagle Aquila chrysaetos and found that feathers cut in their first year of use were replaced, on average, after 11.4 months, whereas uncut feathers before and during the experiment were moulted, on average, after 24 months of use. Feather cutting advanced moult, on average, in excess of a year and thereby demonstrates the existence of a previously undescribed neurophysiological mechanism for preferentially replacing damaged feathers.

Parental investment in two large raptors breeding in a high prey density area

We investigated the breeding behaviour of Bearded Vulture Gypaetus barbatus and Golden Eagle Aquila chrysaetos between 2008 and 2011 in the Stelvio National Park (the Alps, Italy), which harbours one of highest densities of wild ungulates in the Alps. Parental care behaviours (incubation and chick brooding, nest attendance, changeover, food provisioning and nestling feeding) were recorded at nests of both species (four Bearded Vulture and 14 Golden Eagle pairs). Differences in investment between sexes and periods were found in both species: the time spent in incubation and nest attendance was higher in females and decreased with the progress of the breeding season (from incubation to post-hatching and to pre-fledging). A significant effect of the interaction between sex and period was also found. Compared to the literature, our results suggest a lower contribution by Bearded Vulture males, whereas Golden Eagle males spent more time in incubation and nestling brooding than reported. The higher investment shown by Golden Eagle males in our study area may be due to the high availability of live prey and ungulate carrion, which could allow males to spend less time in hunting, resulting in more time at the nest. Most changeovers for both species took place in the central hours of the day. No difference in food provisioning was observed between the sexes of the two species, consistent with information available for Bearded Vultures, but not for Golden Eagles. The patterns we found revealed a female-biased investment (unexpected for the Bearded Vulture), although males significantly contributed to nest behaviour, especially during the incubation period (unexpected for Golden Eagles). The large amounts of natural prey and carrion in the study area may contribute to the nest behaviour of these large raptors.

Forecasting disturbance effects on wildlife: tolerance does not mitigate effects of increased recreation on wildlands

There is widespread evidence that human disturbance affects wildlife behavior, but long-term population effects can be difficult to quantify. Individual-based models (IBMs) offer a way to assess population-level, aggregate effects of disturbance on wildlife. We created Tolerance in Raptors and the Associated Impacts of Leisure Sports (TRAILS), an IBM that simulates interactions between recreationists and nesting raptors, to assess the effect of human disturbance on raptor populations and test if changes in tolerance to disturbance could mitigate negative consequences. We used behavioral and demographic data from golden eagles Aquila chrysaetos, and recreation activity data to parameterize TRAILS and simulate the effects of pedestrian and off-highway vehicle (OHV) recreation on the likelihood of territory occupancy, egg-laying and nest survival of eagles over 100 years. We modeled eagle populations in the absence of recreation, with stationary 2014 levels of recreation, and with annual increases in recreation. Furthermore, we simulated eagles that developed tolerance to disturbance randomly, through natural selection, habitat imprinting, or habituation. In the presence of recreation, simulated eagle populations had significantly lower and more variable growth rates, population sizes and territory occupancy. Annual increases in recreation of 1–2% greatly exacerbated population declines. Though both habituation and natural selection lead to more tolerant eagle populations, neither buffered eagle populations from detrimental effects of recreation. These results suggest that long-lived species that experience encroachment from human activities may not adapt to human disturbance at a rate that compensates for changes in disturbance. This project illustrates the usefulness of IBMs for evaluating non-lethal threats, forecasting population changes and testing theoretical feedbacks in system processes.

Habitat selection by adult Golden Eagles Aquila chrysaetos during the breeding season and implications for wind farm establishment

ABSTRACTCapsule: Global Positioning System (GPS)-tagged adult Golden Eagles Aquila chrysaetos breeding in forests in northern Sweden selected clear-cuts, coniferous forests with lichens and steep slopes during the breeding season but avoided wetlands and mixed forest.Aims: To investigate the habitat selection patterns of tree-nesting Golden Eagles, and identify how potential conflicts with wind farm development could be minimized.Methods: The study is based on GPS tracking data from 22 adult eagles. We estimated home range sizes using a biased random bridge approach and habitat selection patterns using resource selection functions following a use-availability design.Results: Core home range size among adults was variable during the breeding season (5–30 km2). Individual movement extents were variable, but sexes did not significantly differ in their scale of movement. At the landscape scale, individuals selected for clear-cuts and coniferous forest with ground lichens, whereas wetland, water bodies and mixed forest were avoided. Steeper and south facing slopes were selected for, whereas, north facing slopes were avoided.Conclusions: Potential conflicts between eagles and wind energy establishment can be reduced if wind farms are placed away from steep slopes, minimizing areas that are clear-cut during construction, and locating turbines within dense, young and other less favoured forest habitats.

Итоги проекта «Оценка влияния воздушных линий электропередачи средней мощности на орнитофауну Мангистауской области (Республика Казахстан)»

The article highlights the project results on the assessment of the impact of middle voltage overhead power lines (PL) on avifauna of Mangistau region of the Republic of Kazakhstan. On repeated examination of 440 km of PL there was determined a fact of death of 123 birds belonging to 29 species. In particular, 23 birds died from injuries because of collision with wires, and 100 birds were electrocuted. Among the latter, about 60 % are eagles (Steppe Eagle Aquila nipalensis, Golden Eagle Aquila chrysaetos, Imperial Eagle Aquila heliaca). There is the dependence of a number of electrocuted birds on the engineering design of PL. There was an extrapolation of the bird electrocution survey results on the whole territory of Mangistau region.

The Bald and Golden Eagle Protection Act, Species-Based Legal Protection and the Danger of Misidentification

The Bald and Golden Eagle Protection Act of 1940 bestows legal protection on two North American eagle species in the United States of America. The Act was originally aimed at the legal protection of only one species: the Bald Eagle Haliaeetus leucocephalus, the national symbol of the USA. Later the Act was amended to extend protection also to the Golden Eagle Aquila chrysaetos. The Bald Eagle was an Endangered Species, but the Golden Eagle was not formally listed as Endangered nationwide in the USA. One of the reasons for extending legal protection to the Golden Eagle under the Act was to strengthen the legal protection of the Bald Eagle, because immature Bald Eagles were being misidentified as Golden Eagles and shot. Additional factors relating to Golden Eagle mortality also made legal protection of the Golden Eagle desirable. The danger that a rare and legally protected species can be misidentified and mistaken for a more common and unprotected species can therefore serve as a reason for bestowing legal protection on the more common species as well. Other factors may also indicate that legal protection of the more common species is desirable, making the case more compelling. If this line of reasoning is applied in respect of South African birds of prey, a strong case can be made in favour of extending legal protection under the national biodiversity legislation to more species than the small number of species currently enjoying such protection. Species that are listed as Vulnerable under South African national biodiversity legislation may be misidentified as species that are not subject to such protection. Additional factors are also present that make such an extension of legal protection desirable. &#x0D;