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Golden eagles inhabit a wide range of habitats across western North America and exhibit complex, large-scale patterns of movement and migration. Conservation planning for golden eagles–whether focused on siting development of renewable energy resources, prioritization of areas for compensatory mitigation actions, or resource management on public lands–is therefore reliant on spatially explicit predictive models of golden eagle distribution and density. Working with a host of collaborators from federal, state and tribal wildlife agencies, research institutions, and private industry, the U.S. Fish and Wildlife Service (Service) developed and tested a series of species distributional models to provide a consistent spatial foundation for golden eagle conservation in the western United States.
The regional-scale distribution and density of golden eagles is influenced by three overlapping life history stages; breeding, dispersal and migration, and overwintering. The size and life history composition of the golden eagle population in a landscape may change seasonally. For example, a given landscape may support only scattered breeding eagles in summer, serve as a corridor for hundreds of migrating eagles in fall, and then contain many migrant and dispersing eagles during winter; in addition to the resident breeding pairs. Conservation planning for golden eagles must therefore consider life history stages and seasonal variation in eagle distribution and density. Our modeling framework therefore sought to reliably predict the relative density of golden eagles throughout the western conterminous United States during breeding, seasonal dispersal and migration periods, and overwintering.
Our models are intended for application in regional-scale conservation planning and proactive risk assessments (“desk-top analyses”) in support of development siting and prioritization of areas for management action or protection. Model resolution may not be appropriate for applications at finer scales, such as siting individual turbines within a project area. Models available on ServCat are considered final versions. Revision and refinement of these models may occur in the future as new data generated from surveys, telemetry studies, and field application become available.
Golden eagle breeding territories are occupied by the most demographically valuable segment of their populations (territorial adults) and serve the critical function of supporting all reproduction. Territorial golden eagles in the western contiguous United States are largely year-round residents, extending the importance of breeding areas to eagle fitness beyond the breeding season. Understanding and accurately predicting the distribution and density of suitable breeding sites is therefore a fundamental component of conservation planning for golden eagles. To address this need, the Service worked with research partners and numerous collaborators throughout the West to develop predictive models of golden eagle breeding habitat encompassing all or portions of 17 states.
Breeding habitat models were based on golden eagle nest records obtained from state, federal, tribal, and private entities. To ensure that our sample was broadly representative of regional environmental conditions, we supported or conducted new surveys to identify nest locations in geographic areas where nest records were lacking. We accounted for regional variability in habitat availability by partitioning the eagle’s range based on CEC Level III ecoregions, and developed separate models for each ecoregion. We used literature review and input from eagle experts to identify appropriate spatial scales to evaluate and a broad range of candidate variables including terrain, land cover, human development, climate, and wind/uplift for evaluation in the modeling process.
Because our models are intended to directly support eagle conservation and management actions such as siting of energy development and prioritization of areas for mitigation or protection, we rigorously evaluated the performance of each ecoregional model and provide the evaluation results to end users. Model results are predictions of relative nest density and are accurately scaled to actual nest density rather than “simply” discriminating nest from non-nest sites. That is, the models have the ability to determine that one area, for example, has 12 times the predicted density of breeding sites as another area; as opposed to “more” nests.
Models available on ServCat are considered final versions. Revision and refinement of the models, particularly for ecoregions with low sample sizes, may occur in the future as new data from surveys and field application become available.
Seasonal variation in golden eagle distribution and density poses a challenge for development of effective conservation strategies for the species. Breeding areas are often prioritized in eagle conservation and management, but the distribution of golden eagles may differ substantially between breeding and nonbreeding seasons. In winter the western coterminous U.S. receives a large influx of migrant golden eagles from Canada and Alaska, resident adult eagles may move beyond breeding-season ranges seeking carrion or other food resources, and many juvenile and subadult eagles make regional-scale dispersal movements to winter ranges. These shifts in golden eagle distribution during winter are an important component of risk assessments and conservation planning, but have not been systematically described.
To address this need, the Service worked with research partners and numerous collaborators throughout the West to develop predictive models of the winter distribution and relative density of golden eagles in western North America. Our winter distribution models are based on satellite telemetry data from ~ 800 individual golden eagles, provided by a North America-wide network of more than 30 cooperators. Because our objective was to identify habitats used by overwintering golden eagles (as opposed to actively migrating or dispersing), we differentiated between transiting (rapid, directional movements) and sedentary (irregular, non-directional movement) behaviors, and developed models using only sedentary locations occurring between November and March. We related these locations to variables such as terrain, land cover, human development, climate, and wind/uplift to create winter habitat models. We accounted for regional variability in habitat availability by partitioning the eagle’s range based on The Nature Conservancy’s ecoregions, and developed separate models for each ecoregion.
Our model predictions may be interpreted as relative density of use by golden eagles during winter, and are appropriate for use in eagle conservation and management actions such as siting of energy development and prioritization of areas for mitigation or protection. Models available on ServCat are considered final versions. Revision and refinement of the models, particularly for regions with low sample sizes, may occur in the future as new data from ongoing telemetry studies become available.
Golden eagles exhibit a broad range of seasonal movement behaviors, influenced by geographic origin, age, breeding status, and annual variation in prey resources. Populations inhabiting boreal and arctic regions are obligate migrants (all age classes migrate long distances), whereas many/most individuals in more southerly temperate regions do not migrate. The resulting seasonal variation in density and composition of golden eagles occupying western landscapes presents a challenge for appropriate siting of development projects, and for wildlife managers assessing the risks posed by development proposals. To address this challenge, the Service worked with research partners and numerous collaborators to develop predictive models of golden eagle “movement habitat” encompassing western North America.
Our movement models are based on satellite telemetry data from ~ 800 individual golden eagles, provided by a North America-wide network of more than 30 cooperators. Because our objective was to identify landscape and climate features associated with dispersal and migration by golden eagles, we differentiated between transiting (rapid, directional movements) and sedentary (irregular, non-directional movement) behaviors, and used only transiting locations for movement modeling. We then related movement locations to variables such as terrain, land cover, human development, climate, and wind/uplift to create movement habitat models.
Because our sample of telemetry data represented both long-distance migration and local movements by golden eagles, we developed seasonal models at two scales: western North America, and western conterminous U.S. Our western North America-scale models of spring and fall transiting are more general, and are intended to highlight consistent large-scale patterns of movement habitat. Models constrained to the conterminous U.S. are intended to identify specific areas that are of varying value to transiting eagles, at a scale appropriate for site planning or conservation prioritization.
Our model predictions may be interpreted as relative density of use by migrating and dispersing golden eagles, and are appropriate for use in eagle conservation and management actions such as siting of energy development and prioritization of areas for mitigation or protection.
Models available on ServCat are considered final versions. Revision and refinement of the models, particularly for regions with low sample sizes, may occur in the future as new data from ongoing telemetry studies become available.
Occupancy and reproduction at breeding territories are important components of golden eagle population demography, and are a primary focus of the species’ conservation and management. To this end, protections are typically focused on buffering occupied nests from disturbance. Territorial golden eagles may, however, exhibit behavioral and physiological responses to disturbance and habitat alteration at a variety of spatial scales surrounding their nest sites. Two spatial scales commonly used in evaluation of animal space-use are home ranges and core areas. During the breeding season, territory defense and nest tending serve to anchor territorial eagles to disproportionately used ‘core areas’ surrounding their nest sites. The size and spatial configuration of home ranges, on the other hand, are influenced by the distribution of prey and their habitats in the landscape and are subsequently larger and more variable in size. Published estimates of golden eagle home range and core area sizes are available for some areas, but their application in eagle management is limited by small sample sizes, wide variation in estimation methods used and seasonal range of data analyzed, and ecological differences between study animals or populations.
To address this issue, the Service and numerous collaborators analyzed telemetry data from 142 territorial adult golden eagles distributed across North America. We used a consistent methodology to estimate home range and core area sizes, and evaluated geographic and seasonal differences in space-use estimates. The resulting estimates of golden eagle core area and home range sizes are intended for use in evaluating potential effects of disturbance and habitat alteration in the vicinity of golden eagle breeding sites, and establishing appropriate buffers to avoid or minimize effects of proposed projects on territorial golden eagles.