James W. Watson

ANNUAL MIGRATIONS OF BALD EAGLES TO AND FROM CALIFORNIA

ABSTRACT We fitted four nestling Bald Eagles (Haliaeetus leucocephalus) with Doppler-based satellite Platform Transmitter Terminals (PTTs) in northern California in 1997–1999. We also fitted immature and adult Bald Eagles with apparent origins in Canada with PTTs on their wintering grounds in central and southern California in 1997–2002. Post-fledging California eagles moved northward in their first summer, three to coastal and near-coastal central British Columbia and one to Great Slave Lake in Canadas Northwest Territories (ca. 1200–1400 and 2200 km by straight line, respectively). Three eagles with still-functioning PTTs returned to California between October and April. In subsequent years, the California-fledged eagles returned to or near their original northern summer areas in British Columbia or Northwest Territories annually for as many as 2 yr. Migrations of one young California eagle to and from Great Slave Lake were geographically similar to those of adult and immature Bald Eagles we studied concurrently that spent the breeding season in Canada and wintered in California, but timing of movements differed. In migrations subsequent to their first year, California eagles departed California later (late May to late July) than wintering migrants of all ages (mid-February to mid-March), and returned as early as September, while the winter migrants did not arrive in California until December–January.

Focal Activity of Nesting Golden Eagles near Unused Nests

ACTIVIDAD FOCAL DE INDIVIDUOS DE AQUILA CHRYSAETOS ANIDANDO CERCA DE NIDOS SIN UTILIZAR La protección de los nidos usados por individuos de Aquila chrysaetos y la aplicación de zonas de amortiguamiento que minimicen los efectos de las actividades humanas asociadas son prácticas de conservación aceptadas. La necesidad de proteger y de crear zonas de amortiguamiento para nidos no utilizados de águilas es menos clara. Analizamos la intensidad de los comportamientos funcionales, o actividad focal, de 14 individuos adultos de A. chrysaetos rastreados por telemetría en nidos usados y sin uso en relación a sus ámbitos de hogar completos en el este de Washington y Oregón entre 2005 y 2013. La actividad focal de las águilas en áreas con nidos sin uso fue variable y típicamente menor que la que ocurrió cerca de los nidos usados, pero casi todos los nidos sin uso se ubicaron dentro de las zonas núcleo de las áreas de acción de las águilas. Los nidos sin uso se ubicaron en zonas de alto uso de los ámbitos de hogar, incluso cuando estuvieron separados por >1 km de los nidos utilizados y aparentaron haber estado sin uso por varios años. Las águilas pueden haber sido atraídas a las áreas cercanas a nidos sin uso debido a la preferencia de perchas o de condiciones de vuelo, o la actividad focal cerca de los nidos sin uso puede haber desempeñado una función territorial. Debido a que las águilas se mudaron a nidos ubicados hasta a 2.5 km de los nidos ya utilizados, no pudimos identificar nidos que no se beneficiarían de la zona de amortiguamiento protectora y concluimos que todos los nidos sin utilizar ameritan zonas de amortiguamiento protectoras.

Comparative Diets of Nesting Golden Eagles in the Columbia Basin Between 2007–2013 and the Late 1970s

In 1991, the Golden Eagle (Aquila chrysaetos) was identified as a candidate for state listing in Washington as a result of concerns about this species’ population status. Concurrent with the designation has been a continued widespread conversion of shrub-steppe habitats to agriculture (Vander Haegen and others 2000) and potential for associated changes in eagle prey. In the late 1970s, Marr and Knight (1983) examined food habitats of Golden Eagles on 38 territories in eastern Washington and found nearly equal numbers of avian and mammalian prey, ,1% of jackrabbits (Lepus californicus and Lepus townsendi) and ground squirrels (Urocitellus spp.), and 42% Yellow-bellied Marmots (Marmota flaviventris), which was unusually high (Knight and Erickson 1978). It is unknown whether these species are representative of current diets of nesting Golden Eagles in the Columbia Basin. In this paper we provide a dietary analysis of nesting eagles based on prey collected throughout the Columbia Basin from 2007–2013 and compare the results to diets from the late 1970s. Habitat in the Columbia Basin is characterized by open expanses of shrub-steppe and grasslands along major rivers (Vander Haegen and others 2000). Fruit orchards and irrigated farmland surround much of the native habitat used by eagles, especially where terrain is level enough to be farmed. Golden Eagles most often nest along cliff faces above basins and forage along open hillsides and in draws (Watson and others 2014). These eagles also nest in mature and over-mature Ponderosa Pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) trees at higher elevations along the foothills away from the drainage basins. We collected prey remains in and below the Golden Eagle nests throughout the Columbia Basin (Fig. 1). Prey were collected once at each nest in 2007–2013, from July to August, after young eagles fledged. When prey were limited or absent in the nest on the initial visit, we visited and resampled the nest in a subsequent year. Marr and Knight (1983) used a similar sampling protocol in the 1970s and visited nests once per season, with some nests visited multiple years. We also resampled 2 nests where we installed trail cameras (Reconyx Rapidfire) for 1 season between May and July to test their efficacy in assessing diets and to compare frequencies of relatively large (.1 kg) prey and small prey documented by the 2 methods. Large prey may be overrepresented in raptor diets that are assessed by collecting prey during only 1 nest visit (Marti and others 2007). We prioritized visits to nests sampled by Marr and Knight (1983), most of which were in north-central Washington (Fig. 1), but were only able to sample nests on 5 of the same territories. Most territories (68%) studied in the 1970s were unoccupied during our study, and 34% have been unoccupied since the 1980s (Washington Department of Fish and Wildlife, Wildlife Survey Data Management Database, G Blatz, 600 Capitol Way N, Olympia, WA 98501). The rest of the territories were not visited primarily because of a lack of permission to trespass, or unsafe climbing conditions. Thus, we limited prey comparisons between the 2 studies to a general comparison of frequencies of major taxa with a chi-square contingency test rather than testing for prey changes on specific territories. From each prey sample, which included prey remains and pellets, we derived the minimum number of individuals down to the most specific taxa possible through identification of major bones and bone fragments (Searfoss 1995; Elbroch 2006) matched with fur and feathers (Moore and others 1974; Scott and McFarland 2010). We computed prey biomass derived from frequency and published mass values for adult and young prey species. For GENERAL NOTES

Lead, Mercury, and DDE in the Blood of Nesting Golden Eagles in the Columbia Basin, Washington

Plomo, Mercurio y DDE en la Sangre de Individuos Reproductores de Aquila chrysaetos en la Cuenca de Columbia, Washington La toxicosis ocasionada por la ingestion de plomo (Pb) es una preocupacion creciente para las poblaciones de Aquila chrysaetos a lo largo del oeste de America del Norte. Analizamos muestras de sangre para Pb, mercurio (Hg) y compuestos organoclorados (COs) de 17 individuos adultos de A. chrysaetos capturados entre 2005 y 2013 en la Cuenca de Columbia, en el este de Washington. La mayoria (65%) de las aguilas presento niveles elevados de Pb, incluyendo un 24% con niveles que indican una exposicion cronica al Pb que podria producir efectos clinicos. Se detectaron niveles bajos de Hg y COs. Sugerimos que existen motivos de preocupacion sobre los posibles efectos de la ingesta de Pb en esta poblacion reproductora de A. chrysaetos y sospechamos que la fuente mas probable de Pb en esta region es la carrona generada por caceria con balas que se encuentra ampliamente disponible para las aguilas...

Spatial and Temporal Patterns in Golden Eagle Diets in the Western United States, with Implications for Conservation Planning

Abstract 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.

Golden Eagles (Aquila chrysaetos) Build New Nest Below Cliff and Provision Fallen Nestling

During the post-fledging dependence period, juvenile raptors, including Golden Eagles (Aquila chrysaetos; Kochert, Steenhof, McIntyre, and Craig 2002, in A. Poole and F. Gill [EDS.], The birds of North America, No. 684, The Academy of Natural Sciences, Philadelphia, PA and The American Ornithologists’ Union, Washington, DC U.S.A.), that fledge from elevated nests and are grounded are often provisioned by the adults while they develop their flight skills. Less certain is the fate of nestling raptors that are displaced from nests prematurely and survive the fall to the ground. We are unaware of reports that document successful rearing of displaced raptor nestlings on the ground and report here on such an occurrence at a Golden Eagle nest. The Toroda Creek Golden Eagle nest territory (Washington Department of Fish and Wildlife [WDFW] occurrence record # 144) contains two nests on east-facing cliffs. The WDFW monitored this nest territory for 15 of 28 yr between 1979–2006; Golden Eagle occupancy was verified in 9 of the 15 yr, and 8 juveniles were produced in 6 yr. On 6 April 2006, using binoculars and a spotting scope from ground-based vantage points, we observed an adult Golden Eagle in incubation posture on one of the nests. On 30 May 2006, we rechecked the nest and within 30 min observed the pair of adult Golden Eagles deliver several sticks and green-needled branchlets of Douglas-fir (Pseudotsuga menziesii) to the talus directly below the cliff nest. We also observed an apparently uninjured nestling, 4–5 wk old (Hoechlin 1974, Western Birds 7:137–152), standing on the talus adjacent to the newly delivered sticks and branches. No other young were present on the ground or in the cliff nest that remained intact. We suspect that the juvenile had accidentally fallen out of the cliff nest, survived the fall to the ground, and that the adults were provisioning it on the ground and building a new nest on the ground next to the nestling. We rechecked the nest on 16 June 2006 and observed the nestling standing in a newly constructed nest near the highest point in the talus, ca. 30 m below the cliff nest (Fig. 1). On 20 June 2006, we observed the nestling in the new ground nest; the nestling was nearly totally feathered with dark contour feathers and appeared to be about 8 wk old (Hoechlin 1974). On 7 July 2006, we visited and photographed the new, but empty, ground nest. The nest contained a few green conifer sprigs, some fecal whitewash, and several fresh prey remains, including a leg of a deer fawn, miscellaneous bird feathers, and tarsi and metatarsi possibly from a Dusky Grouse (Dendragapus obscurus). We did not observe a juvenile in the nest or in the nearby area during our short (,1 hr) visit to the nest; however, we observed one adult Golden Eagle flying overhead. Our repeated observations confirmed that the adults built a new ground nest and provisioned the nestling for at least 3 wk, and likely to fledging age.—Dana L. Base and Steve Zender (email address: BaseDLB@dfw.wa. gov), WDFW, 2315 N. Discovery Place, Spokane Valley, WA 99216 U.S.A.; and James W. Watson, WDFW, 600 Capitol Way N., Olympia, WA 98501 U.S.A.

Prevalence and Risk Factors of Trichomonas Gallinae and Trichomonosis in Golden Eagle (Aquila chrysaetos) Nestlings in Western North America

Abstract Avian trichomonosis, caused by the protozoan Trichomonas gallinae, affects bird-eating raptors worldwide. Raptors can develop trichomonosis by feeding on infected prey, particularly Rock Pigeons (Columba livia), which are a reservoir for T. gallinae. Raptors may be particularly vulnerable to T. gallinae infection in degraded habitats, where changes in resources may cause raptors to switch from foraging on native prey to synanthropic avian species such as Rock Pigeons. Golden Eagles (Aquila chrysaetos) typically forage on mammals; however, habitat across much of their range is experiencing degradation through changes in land use, climate, and human encroachment. In 2015, we examined the prevalence of T. gallinae infection in Golden Eagle nestlings across western North America and conducted an intensive study on factors associated with T. gallinae infection and trichomonosis in southwestern Idaho. We found T. gallinae infection in 13% (12/96) of eagle nestlings across 10 western states and in 41% (13/32) of nestlings in southwestern Idaho. At the Idaho site, the probability of T. gallinae infection increased as the proportion of Rock Pigeons in nestling diet increased. Nestlings with diets that consisted of ≥10% Rock Pigeons had a very high probability of T. gallinae infection. We compared historical (1971–81) and recent (2014–15) diet data and incidence of trichomonosis lesions of nestling eagles in Idaho and found that the proportion of Rock Pigeons in eagle diets was higher in recent versus historical periods, as was the proportion of eagle nestlings with trichomonosis lesions. Our results suggested that localized shifts in eagle diet that result from habitat degradation and loss of historical prey resources have the potential to affect Golden Eagle nestling survival and supported the hypothesis that land use change can alter biologic communities in a way that might have consequences for disease infection and host susceptibility.

Patterns of Spatial Distribution of Golden Eagles Across North America: How Do They Fit into Existing Landscape-scale Mapping Systems?

Abstract Conserving wide-ranging animals requires knowledge about their year-round movements and resource use. Golden Eagles (Aquila chrysaetos) exhibit a wide range of movement patterns across North America. We combined tracking data from 571 Golden Eagles from multiple independent satellite-telemetry projects from North America to provide a comprehensive look at the magnitude and extent of these movements on a continental scale. We compared patterns of use relative to four alternative administrative and ecological mapping systems, namely Bird Conservation Regions (BCRs), U.S. administrative migratory bird flyways, Migratory Bird Joint Ventures, and Landscape Conservation Cooperatives. Our analyses suggested that eagles initially captured in eastern North America used space differently than those captured in western North America. Other groups of eagles that exhibited distinct patterns in space use included long-distance migrants from northern latitudes, and southwestern and Californian desert residents. There were also several groupings of eagles in the Intermountain West. Using this collaborative approach, we have identified large-scale movement patterns that may not have been possible with individual studies. These results will support landscape-scale conservation measures for Golden Eagles across North America.