Interannual Golden Eagle (Aquila chrysaetos) Nest-Use Patterns in Central Utah: Implications for Long-Term Nest Protection

Unintended effects of recreational activities in protected areas are of growing concern. We used an adaptive-management framework to develop guidelines for optimally managing hiking activities to maintain desired levels of territory occupancy and reproductive success of Golden Eagles (Aquila chrysaetos) in Denali National Park (Alaska, U.S.A.). The management decision was to restrict human access (hikers) to particular nesting territories to reduce disturbance. The management objective was to minimize restrictions on hikers while maintaining reproductive performance of eagles above some specified level. We based our decision analysis on predictive models of site occupancy of eagles developed using a combination of expert opinion and data collected from 93 eagle territories over 20 years. The best predictive model showed that restricting human access to eagle territories had little effect on occupancy dynamics. However, when considering important sources of uncertainty in the models, including environmental stochasticity, imperfect detection of hares on which eagles prey, and model uncertainty, restricting access of territories to hikers improved eagle reproduction substantially. An adaptive management framework such as ours may help reduce uncertainty of the effects of hiking activities on Golden Eagles.

In this chapter, we demonstrate the application of the various classes of thresholds, detailed in earlier chapters and elsewhere, via an actual but simplified natural resource management case study. We intend our example to provide the reader with the ability to recognize and apply the theoretical concepts of utility, ecological and decision thresholds to management problems through a formalized decision-analytic process. Our case study concerns the management of human recreational activities in Alaska’s Denali National Park, USA, and the possible impacts of such activities on nesting Golden Eagles, Aquila chrysaetos. Managers desire to allow visitors the greatest amount of access to park lands, provided that eagle nesting-site occupancy is maintained at a level determined to be acceptable by the managers themselves. As these two management objectives are potentially at odds, we treat minimum desired occupancy level as a utility threshold which, then, serves to guide the selection of annual management alternatives in the decision process. As human disturbance is not the only factor influencing eagle occupancy, we model nesting-site dynamics as a function of both disturbance and prey availability. We incorporate uncertainty in these dynamics by considering several hypotheses, including a hypothesis that site occupancy is affected only at a threshold level of prey abundance (i.e., an ecological threshold effect). By considering competing management objectives and accounting for two forms of thresholds in the decision process, we are able to determine the optimal number of annual nesting-site restrictions that will produce the greatest long-term benefits for both eagles and humans. Setting a utility threshold of 75 occupied sites, out of a total of 90 potential nesting sites, the optimization specified a decision threshold at approximately 80 occupied sites. At the point that current occupancy falls below 80 sites, the recommended decision is to begin restricting access to humans; above this level, it is recommended that all eagle territories be opened to human recreation. We evaluated the sensitivity of the decision threshold to uncertainty in system dynamics and to management objectives (i.e., to the utility threshold).

During a five‐year period, 1975–1979, a total of 2881 prey individuals of 65 prey species were collected at 162 golden eagle nests from northern Sweden and from the island of Gotland. In northern Sweden birds are taken in higher numbers than mammals but calculated as weight the two categories are of equal importance, The main prey during the breeding season are capercaillie, black grouse, willow grouse, ptarmigan, mountain hare and reindeer fawns which together form 91% of the total food biomass. The capercaillie and the black grouse are taken more in the southern part of the coniferous region than in the northern. In contrast, in northern areas, reindeer fawns are more preyed upon than in the South, Ptarmigan and willow grouse are the most commonly captured prey species in mountain areas. The total number of reindeer fawns taken (dead and/or alive) by the Swedish golden eagle population during one summer is estimated at 600 individuals. On Gotland the golden eagles take mammals more often than in its northern distribution area. Rabbit and hedgehog arc the most important species.

Species–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.

We examined regional and temporal variations in prey selection by Golden Eagles Aquila chrysaetos during the nestling period in Japan. We made direct video recordings of a pair of Golden Eagles in Akita prefecture as they delivered prey to the nest for two consecutive nestling periods. We also assembled data from previous studies in Japan, eventually obtaining 14 data sets with which we compared prey composition during nestling periods. Among them, four sets of data were recorded daily by video and used to investigate the temporal change in prey selection and the amount delivered to the nest. The prey item composition varied considerably among the data sets. Japanese Hares Lepus brachyurus were predominantly selected in three data sets, reflecting the lowest dietary breadths that were determined by prey composition. Data sets with higher dietary breadths consisted mainly of Japanese Hares, snakes and Copper Pheasants Syrmaticus soemmerringii. Temporal change in prey selection during nestling periods showed marked variation, but similarities were found in later deliveries of snakes and in total prey weights (83.7–89.9 kg) delivered to successfully fledged broods. Taken together, our results suggest that during nestling periods Golden Eagles in Japan specialized on Japanese Hare. Diet breadth increased through feeding predominantly on snakes, a temporarily available prey, to satisfy the breeding dietary requirement. Regionally varied temporal prey selection may be a key factor for sustaining Eagle populations in the forested mountain habitats of Japan, where prey and habitat conditions change dramatically during the breeding season.

Степной орёл в Алтае-Саянском регионе – результаты исследований 2019–2023 годов

Changes in the distribution and behavior of pathogens and parasites associated with climate change are creating emerging threats for wildlife. These threats have created an urgent need for conservation strategies to manage wildlife. Conservation strategies could provide reliable and cost-effective compensatory mitigation options for protected species affected by renewable energy production, such as golden eagles (Aquila chrysaetos). We used nest camera data to assess survival and cause of death for golden eagle nestlings in southern Idaho, USA. Together, poultry bugs (Haematosiphon inodorus), a blood-sucking ectoparasite that lives in golden eagle nests, and trichomonosis, a fatal disease that is transmitted through the consumption of rock pigeons (Columba livia) caused ~ 27% of nestlings to die per year. From 2022-2023, we treated trichomonosis-infected nestlings with an anti-protozoan drug and developed a protocol for reducing poultry bug densities in eagle nests, then we projected the effects of disease and parasite treatments on population growth using simulation models. We collected pre-treatment information on nestling health and survival, and then, after young fledged, we applied 1 of 3 experimental parasite treatments to eagle nests: permethrin and diatomaceous earth, diatomaceous earth only, or water - a control, and measured effects on eagle health and survival the following year. Ten eagle nestlings with trichomonosis, that otherwise would have died, were successfully treated and lived to fledge from the nest. The permethrin and diatomaceous earth treatment significantly reduced poultry bug densities in eagle nests in the subsequent breeding season and created measurable improvements to nestling health and survival. Nestlings had significantly higher hematocrit, female nestlings had higher mass, and, on average, more nestlings (0.70) successfully survived to fledge compared with control- and diatomaceous earth-treated nests. Further, treatment of disease and parasites was projected to increase population growth rates by 4% and 8%, respectively. In total, we estimate saving 17.5 nestlings, which equates to 10.2 adult eagles, through disease and parasite treatments in two years. In areas with dense concentrations of poultry bugs or where eagles consume rock pigeons, disease and parasite treatments could be an effective compensatory mitigation option or management tool with population-level impacts on eagle populations.

Rapid loss of native shrubs and expansion of invasive annual plants like cheatgrass (Bromus tectorum) have altered North American shrub-steppe systems across extensive areas. Predators, like Aquila chrysaetos (Golden Eagle) that forage on shrub-reliant prey, may abandon historically occupied territories or increase their territory size to cope with degraded habitat. We used a multiseason Bayesian occupancy model that accounted for imperfect detection to investigate the associations between landscape cover, fire history, conspecific neighbor density, and occupancy of 36 A. chrysaetos territories in southwestern Idaho and the Morley Nelson Snake River Birds of Prey National Conservation Area, USA from 1986 to 2022. The probability of A. chrysaetos occupancy at historically occupied territories decreased 25% from 1986 to 2022 (0.83–0.58). Once territories became vacant for 5 yr, they tended to remain vacant, suggesting that they were no longer suitable for eagles, or that no new eagles were recruiting into the population. Territory occupancy was positively associated with shrub cover (β: 0.90, 95% CrI: 0.12 to 1.71) and negatively (albeit weakly) associated with annual herbaceous cover (β: –0.63, 95% CrI: –1.32 to 0.05). Territories closer to other occupied territories had a lower probability of occupancy than territories with distant neighbors (β: –3.89, 95% CrI: –4.61 to –3.14), likely because eagles compensated for degraded habitat by expanding their territories. Years since the territory last burned had a slightly positive effect on occupancy with high uncertainty and a credible interval that overlapped 0 (β: 0.28, 95% CrI: –0.26 to 0.87). The probability of detecting eagles in an occupied territory was high (0.90) and improved in surveys conducted earlier in the day and later in the breeding season. Shrub conversion to invasive grasslands has negative bottom-up consequences on A. chrysaetos territory occupancy, which may decrease the local carrying capacity for eagles in this area.

One of the central goals of the field of population ecology is to identify the drivers of population dynamics, particularly in the context of predator–prey relationships. Understanding the relative role of top‐down versus bottom‐up drivers is of particular interest in understanding ecosystem dynamics. Our goal was to explore predator–prey relationships in a boreal ecosystem in interior Alaska through the use of multispecies long‐term monitoring data. We used 29 years of field data and a dynamic multistate site occupancy modeling approach to explore the trophic relationships between an apex predator, the golden eagle, and cyclic populations of the two primary prey species available to eagles early in the breeding season, snowshoe hare and willow ptarmigan. We found that golden eagle reproductive success was reliant on prey numbers, but also responded prior to changes in the phase of the snowshoe hare population cycle and failed to respond to variation in hare cycle amplitude. There was no lagged response to ptarmigan populations, and ptarmigan populations recovered quickly from the low phase. Together, these results suggested that eagle reproduction is largely driven by bottom‐up processes, with little evidence of top‐down control of either ptarmigan or hare populations. Although the relationship between golden eagle reproductive success and prey abundance had been previously established, here we established prey populations are likely driving eagle dynamics through bottom‐up processes. The key to this insight was our focus on golden eagle reproductive parameters rather than overall abundance. Although our inference is limited to the golden eagle–hare–ptarmigan relationships we studied, our results suggest caution in interpreting predator–prey abundance patterns among other species as strong evidence for top‐down control.

Management of emerging pathogen and parasite threats could provide cost‐effective compensatory mitigation options for protected species, such as golden eagles ( Aquila chrysaetos ). Golden eagle nestlings are vulnerable to infestations of poultry bugs ( Haematosiphon inodorus ), a blood‐sucking ectoparasite that lives in nest material and trichomonosis, a highly lethal disease caused by the protozoan Trichomonas spp. We aimed to develop effective treatment protocols for poultry bugs and trichomonosis and project whether nestling parasite and disease management would have population‐level effects in this long‐lived apex predator. We collected pre‐treatment data on poultry bug loads in eagle nests; then, we applied 1 of 3 experimental parasite treatments to empty eagle nests in late summer months: a combination of permethrin and diatomaceous earth, diatomaceous earth‐only or water—a control, and measured effects on poultry bugs and nestlings the following year. During nestling exams, we treated trichomonosis‐infected nestlings with an anti‐protozoan drug. Then, we projected the effects of treatments on population growth using simulation models. The permethrin and diatomaceous earth nest treatment significantly reduced poultry bug densities in the subsequent breeding season and improved nestling health and survival. Nestlings had significantly greater haematocrit; female nestlings had greater mass, and, on average, 0.70 more nestlings successfully survived to fledge compared with control‐ and diatomaceous earth‐only‐treated nests. Ten eagle nestlings from 27 nests that likely would have died from trichomonosis lived to fledge from the nest after treatment. Over 2 years, we estimate saving 17.5 nestlings, which equates to 10.2 adult eagles. We projected that treatments of poultry bugs and trichomonosis could increase local eagle population growth rates by 8% and 4%, respectively. Synthesis and applications . For sensitive or at‐risk bird species, treating parasites and disease can improve nest productivity and support population growth, making it a valuable conservation tool. In areas with high concentrations of poultry bugs or where eagles consume avian vectors of Trichomonas spp., pathogen and parasite treatments may serve as an effective mitigation strategy with population‐level benefits for eagles.

Detailed information on diets and predatory ecology of Golden Eagles (Aquila chrysaetos) is essential to prioritize prey species management and to develop landscape-specific conservation strategies, including mitigation of the effects of energy development across the western United States. We compiled published and unpublished data on Golden Eagle diets to (1) summarize available information on Golden Eagle diets in the western U.S., (2) compare diets among biogeographic provinces, and (3) discuss implications for conservation planning and future research. We analyzed 35 studies conducted during the breeding season at 45 locations from 1940–2015. Golden Eagle diet differed among western ecosystems. Lower dietary breadth was associated with desert and shrub-steppe ecosystems and higher breadth with mountain ranges and the Columbia Plateau. Correlations suggest that percentage of leporids in the diet is the factor driving overall diversity of prey and percentage of other prey groups in the diet of Golden Eagles. Leporids were the primary prey of breeding Golden Eagles in 78% of study areas, with sciurids reported as primary prey in 18% of study areas. During the nonbreeding season, Golden Eagles were most frequently recorded feeding on leporids and carrion. Golden Eagles can be described as both generalist and opportunistic predators; they can feed on a wide range of prey species but most frequently feed on abundant medium-sized prey species in a given habitat. Spatial variations in Golden Eagle diet likely reflect regional differences in prey community, whereas temporal trends likely reflect responses to long-term change in prey populations. Evidence suggests dietary shifts from traditional (leporid) prey can have adverse effects on Golden Eagle reproductive rates. Land management practices that support or restore shrub-steppe ecosystem diversity should benefit Golden Eagles. More information is needed on nonbreeding-season diet to determine what food resources, such as carrion, are important for overwinter survival.

Raptors are wide-ranging, vagile avian predators whose populations can be difficult and costly to monitor on their breeding or winter range. However, monitoring raptors during their annual northbound or southbound migration is a cost-effective and efficient alternative to time-intensive, single-species breeding surveys. In 2010, we observed numerous Swainson’s Hawks (Buteo swainsoni) and Red-tailed Hawks (Buteo jamaicensis) migrating through the Hayden Valley in central Yellowstone National Park, prompting an investigation into raptor migration patterns in the park. Our objectives were to monitor annual autumn raptor migration in Hayden Valley from 2011 to 2015 and to determine the relative role of this undocumented migration site by comparing our observations to simultaneously collected migration data from three other sites in the Rocky Mountain Flyway. From 2011 to 2015, we observed 6441 raptors of 17 species across 170 d and 907 h of observation. Red-tailed Hawks, Swainson’s Hawks, and Golden Eagles (Aquila chrysaetos) accounted for 51% of the total individuals observed over five years. Overall counts from Hayden Valley were comparable to counts from the three migration sites in the Rocky Mountains, although abundance of individual species varied by site. Data from this study suggest that Hayden Valley may serve as a stopover site for migrating raptors and presents an opportunity for future research. By improving our understanding of where raptors migrate and the characteristics of stopover areas in the Rocky Mountains, land managers may develop effective strategies for protecting raptor populations and habitat from threats including development and climate change.

SUMMARYThe relative stability of breeding density in the Peregrine and Raven in certain inland districts is examined in relation to population limiting factors. Problems of cenus‐making are considered, particularly the use of alternative nesting places. Breeding populations of the Raven have not fallen below 15% of the maxima since 1945. While the Peregrine now shows signs of local decline, it had numeral stability equal to the Raven during the preceding period, and this is the state under consideration.Of possible controlling factors, food supply is unlikely to be directly limiting. For breeding to occur, cliffs suitable in altitude, vertical height, cover and presence of ledges are necessary. Alternative cliffs and ledges are used if available but are not essential to ensure regular occupation of a territory. Availability of suitable cliffs controls nesting density at the lower levels, but does not impose an upper limit.The Golden Eagle is a dominant competitor for nesting cliffs and perhaps for food, and when nesting space is limited Peregrines and Ravens may compete with each other for cliffs. Deliberate persecution can deplete adult populations temporarily and reduce breeding success, especially in the Peregrine, but does not limit breeding density over a period, except in unsuitable terrain. For both species, breeding success and/or migration are sufficient to maintain numbers in the study regions. When breeding success is high, no increase in nesting populations follows. The Raven has non‐breeding surplus populations during the breeding season but this is less certain for the Peregrine.Although direct evidence for its existence as defence of an area is scanty, territorialism is regarded as the factor controlling maximum nesting density by producing a “proximity tolerance limit” between adjacent nesting pairs. It is believed that such territorialism is not itself an ultimate limiting factor but has evolved in relation to food supply so that the numbers of predators are permanently balanced against this factor.

Eagles as indicators of ecosystem health: Is the distribution of Martial Eagle nests in the Karoo, South Africa, influenced by variations in land-use and rangeland quality?

Many bird species breeding under optimal temperature conditions show higher reproductive success. However, less information can be found about how the reproductive output differs within one population and one breeding season. To find inter and intra-seasonal differences in several aspects of breeding ecology and breeding output we monitored 223 breedings of the White-throated Dippers within the three river basins of northern Slovakia (Central Europe) in 2010–2018. We registered the beginning of egg laying, clutch size, nest success and the proportion of second clutches. There were significant differences in egg-laying commencement between breeding seasons. The mean February and March temperature significantly influenced the first egg day (20 February–18 March), median laying date (8 March–6 April), the interval between the first and the last first egg in all clutches in one breeding season (37–50 days) and the proportion of second clutches (0.77%–0.95%). However, the differences were found not only between different seasons. The egg-laying initiation of individual nests within each season was considerable affected by the altitude and the proportion of second clutches of particular nests was significantly influenced by their timing of egg laying.