Lead poisoning occurs worldwide in populations of predatory birds, but exposure rates and population impacts are known only from regional studies. We evaluated the lead exposure of 1210 bald and golden eagles from 38 US states across North America, including 620 live eagles. We detected unexpectedly high frequencies of lead poisoning of eagles, both chronic (46 to 47% of bald and golden eagles, as measured in bone) and acute (27 to 33% of bald eagles and 7 to 35% of golden eagles, as measured in liver, blood, and feathers). Frequency of lead poisoning was influenced by age and, for bald eagles, by region and season. Continent-wide demographic modeling suggests that poisoning at this level suppresses population growth rates for bald eagles by 3.8% (95% confidence interval: 2.5%, 5.4%) and for golden eagles by 0.8% (0.7%, 0.9%). Lead poisoning is an underappreciated but important constraint on continent-wide populations of these iconic protected species.

AbstractIn the United States, the Bald and Golden Eagle Protection Act prohibits take of golden eagles (Aquila chrysaetos) unless authorized by permit, and stipulates that all permitted take must be sustainable. Golden eagles are unintentionally killed in conjunction with many lawful activities (e.g., electrocution on power poles, collision with wind turbines). Managers who issue permits for incidental take of golden eagles must determine allowable take levels and manage permitted take accordingly. To aid managers in making these decisions in the western United States, we used an integrated population model to obtain estimates of golden eagle vital rates and population size, and then used those estimates in a prescribed take level (PTL) model to estimate the allowable take level. Estimated mean annual survival rates for golden eagles ranged from 0.70 (95% credible interval = 0.66–0.74) for first‐year birds to 0.90 (0.88–0.91) for adults. Models suggested a high proportion of adult female golden eagles attempted to breed and breeding pairs fledged a mean of 0.53 (0.39–0.72) young annually. Population size in the coterminous western United States has averaged ~31,800 individuals for several decades, with λ = 1.0 (0.96–1.05). The PTL model estimated a median allowable take limit of ~2227 (708–4182) individuals annually given a management objective of maintaining a stable population. We estimate that take averaged 2572 out of 4373 (59%) deaths annually, based on a representative sample of transmitter‐tagged golden eagles. For the subset of golden eagles that were recovered and a cause of death determined, anthropogenic mortality accounted for an average of 74% of deaths after their first year; leading forms of take over all age classes were shooting (~670 per year), collisions (~611), electrocutions (~506), and poisoning (~427). Although observed take overlapped the credible interval of our allowable take estimate and the population overall has been stable, our findings indicate that additional take, unless mitigated for, may not be sustainable. Our analysis demonstrates the utility of the joint application of integrated population and prescribed take level models to management of incidental take of a protected species.

We monitored 25 Golden Eagles in Montana, USA, from 2011 to 2015 over 3,601 days using tail-mounted satellite transmitters. Using the best available direct observation and circumstantial evidence, we surmise that only a single eagle (adult female floater) died during monitoring, resulting in a daily survival estimate of 0.9997 (SE = 0.0003) and an annual survival estimate of 0.905 (SE = 0.0907) for a mixture of adult and younger, resident and migrant, breeder and nonbreeder eagles of both genders living in relatively undisturbed regions of the western United States. Under this scenario, adult daily survival averaged 0.9996 (SE = 0.0004) and adult annual survival averaged 0.858 (SE = 0.132).

Studies deploying Platform Transmitter Terminals (PTTs) or Global System for Mobile Communications-GPS (GSM) packages on Golden Eagles have typically used backpack harnesses for attachment despite evidence indicating potential significant negative effects on reproduction and survival. Retention, safety, and utility of tail-mounted PTTs were tested on a sample of Golden Eagles in southwestern Montana. Argos satellite-tracked PTTs of two configurations were attached dorsally or ventrally to the central rectrices of 27 Golden Eagles to study survival. Sixteen packages were known to have been molted or removed (i.e., shed) by the eagle and 13 recovered. Of recovered tail-mounts, six (46%) were forcibly removed by eagles; five by males and one by a female. All packages that were forcibly removed were 32-g ventral mounts. Females tended to retain tail-mounts longer than males and dorsally mounted PTTs tended to be retained longer than those mounted ventrally. Eagles tagged in winter retained PTTs the longest. The duration of tail-mounted PIT retention was adequate for analysis of survival and yielded an adult annual survival rate (86%) consistent with recent U.S. Fish and Wildlife Service estimates (87%). Eight of 13 (62%) territorial adults tagged with PTTs were known to attempt breeding the year they were tracked and six (46%) produced young, rates that did not differ (P > 0.23) from those of a larger sample of the population surveyed during the same period. Logistic regression analysis of cumulative range size by monitoring duration of four territorial adult eagles with tail-mounted GPS indicated that 99% of total range was recorded within 140 d of tracking.

We reviewed band encounter data for Bald Eagles (Haliaeetus leucocephalus) and Golden Eagles (Aquila chlysaetos) to estimate natal dispersal distances for both species in the coterminous United States (U.S.). We filtered band recovery data to focus on individuals banded as nestlings, encountered at ages old enough to be breeding, and encountered at times of the year when they may be at or near breeding or prospective breeding sites. Our final data set included 96 Golden Eagles and 878 Bald Eagles. Distances between banding and subsequent encounter sites for both species were lognormally distributed. We employed both traditional and Bayesian methods of analysis, and obtained similar results from both approaches. Bayesian analysis of banding data suggest a median natal dispersal distance of 69.2 (95% highest density interval [HDI] = 63.5-73.1) km for Bald Eagles and 46.4 (HDI = 36.0-55.2) km for Golden Eagles. Median natal dispersal distance for female Bald Eagles 78.3 was (HDI = 35.4-128.6) km greater than for males; we lacked sufficient data to analyze natal dispersal distance by sex for Golden Eagles. Median Bald Eagle natal dispersal distance did not differ among eight regional populations, but there was evidence of a trend toward increasing natal dispersal distance from east to west across the coterminous U.S. Our findings are compatible with natal dispersal data in the literature for both species. The U.S. Fish and Wildlife Service uses estimated natal dispersal distance of Bald and Golden eagles to set one of the geographic scales at which the effects of permits that authorize the "take" (removal from the wild) of eagles is evaluated. Our analyses suggest that choice of a natal dispersal value in the range of the 50th-90th quantile of the distribution as an effect-area for modeling or effect-assessment for both species of eagle is reasonable. For Golden Eagles, this range is 46-175 km, and for Bald Eagles 69-346 km.

Lead-based rifle bullets, used in game hunting and recreational shooting, fragment when striking bone and soft tissues. Lead fragments may be ingested by birds scavenging offal piles or nonretrieved carcasses and therefore pose a poisoning risk. We captured and sampled 74 Golden Eagles (Aquila chrysaetos) in southwestern Montana, USA, from 2008 to 2010 to evaluate levels of lead, mercury, selenium, and 13 other trace elements in blood and feathers. Lead was detected in blood of most (97%, n=70) eagles; mean blood level was 0.26 parts per million (ppm). Most eagles (65%) had background levels (<0.2 ppm), 29% had elevated levels (0.2–0.5 ppm), 13% had chronic levels (0.51–1.0 ppm), and 3% had acute levels (>1.0 ppm) in blood. Lead in blood decreased from winter to spring. Resident eagles had higher lead levels than eagles of unknown residency. Mercury was detected in few eagles, whereas selenium was detected in all, but at a low level (0.36 ppm). Other chemical elements in blood were at low or biologically appropriate levels. Lead in feathers (n=29) was correlated with blood lead (P=0.010), as was mercury in blood and feathers (n=48; P=0.003). Concentrations of lead and mercury in feathers were higher in adults than in juveniles and immatures (P<0.016) and both elements tended to increase with age. Selenium in feathers (n=48) appeared stable across plumage classes. Although detection rates of lead in blood of eagles captured in spring increased from 1985–1993 to 2008–2010, mean levels decreased (P<0.023) between periods, as did proportions of eagles exhibiting above background levels (>0.2 ppm; P<0.02).

Upper-trophic level piscivores, such as Bald Eagles (Haliaeetus leucocephalus), may be at risk of exposure to environmental contaminants in the western United States from coal-fired power plants and coal-bed methane wells. We collected 64 blood samples from nestling Bald Eagles in southeastern Montana and northwestern Wyoming during 2007-08 for analyses of heavy metals, trace elements, and organochlorine compounds. Mercury was detected in all blood samples and averaged (+/- SD) 0.28 +/- 0.20 ppm. Most nestlings (82.8%) had concentrations near expected background levels, but 7.8% had elevated (>0.7 ppm) mercury levels. Nestlings in Wyoming ((x) over bar = 0.37 +/- 0.22 ppm) had higher blood mercury concentrations than nestlings from Montana ((x) over bar = 0.22 +/- 0.17 ppm; t(31) = 3.151, P = 0.015). In Montana, nestlings sampled on Yellowstone River tributaries had lower blood mercury concentrations ((x) over bar = 0.12 +/- 0.10 ppm) than nestlings from the main stem of the Yellowstone River ((x) over bar = 0.28 +/- 0.21 ppm) and Wyoming ((x) over bar = 0.37 +/- 0.22 ppm; F-2,F-32 = 12.439, P < 0.001). Blood levels of mercury and selenium were positively correlated (r(s) = 0.281, n = 64, P = 0.024). Lead (<(x)over bar> = 0.07 +/- 0.08 ppm) was detected in 81.3% of nestlings, but only 11.5% of those were considered above background levels. The organochlorine p,p'-DDE ((x) over bar = 0.003 +/- 0.003 ppm) was detected in 69.6% of nestlings sampled. Compared to previous studies in the region, mercury contamination has become more widespread, whereas the prevalence of lead contamination was similar to that of the past. Based on this study, we suggest that some Bald Eagle nestlings may be experiencing adverse effects from mercury contamination, and recommend that additional monitoring take place as coal-fired power plants and the coal-bed methane industry continue to expand.

Abstract Blood and feathers of Bald Eagles (Haliaeetus leucocephalus) banded as nestlings (n  =  17), captured as free-flying (n  =  91), or submitted for rehabilitation (n  =  29) in southwestern Montana between December 2005 and April 2008 were sampled for mercury (Hg), selenium (Se), lead (Pb), seven other trace elements, and organochlorines. Hg concentrations in blood (hereafter “HgB”) did not differ between captured eagles and those submitted for rehabilitation, and HgB in both were higher than concentrations in nestlings (P < 0.01). Se concentrations in blood (“SeB”) were similar among groups. Pb concentrations in blood (“PbB”) were higher in captured eagles than in those submitted for rehabilitation (P  =  0.05). No bird submitted for rehabilitation exhibited toxic levels of PbB, but 9% of captured eagles did. HgB and PbB in captured eagles declined as date of capture advanced from autumn to spring. Hg and Se concentrations in feathers (“HgF”; “SeF”) tended to increase with age-class. HgB and SeB, and HgB and HgF were correlated in nestlings and captured eagles (P < 0.05) but not in birds submitted for rehabilitation. Birds captured in autumn during this study had higher HgB (P < 0.05) than birds captured in autumn in the early 1990s, but SeB did not differ. HgB and SeB in birds captured in spring during this study were similar to those of birds captured in spring in the early 1990s, but PbB was lower. Five eagles were recaptured and resampled for contaminants up to 18 yr after initial banding and sampling but no time-trends were detected in contaminant concentrations due to small sample size. Other trace elements and organochlorines if detected in blood were at very low concentrations.

In 1998 and 1999, we determined the spatial distribution, foraging behavior, and reproductive success of ospreys ( Pandion haliaetus (L., 1758)) nesting along the upper Missouri River, Montana. We combined our data with that collected in the same area in 1981–1982 and 1990–1991 to investigate factors influencing settlement patterns. The study area was composed of four distinct habitats, three reservoirs and one free-flowing river section. Although number of occupied nests on each habitat increased from 1981–1982 to 1998–1999, the greatest percentage increases in nest density occurred on habitats previously hypothesized to contain the least prey. Osprey reproductive success was positively related to foraging rates, which differed across habitats, being highest on reservoirs and lowest on the free-flowing river. However, reproductive success was adequate for replacement on each habitat. Most fish consumed by ospreys on each habitat were suckers (Catostomidae), followed by salmonids and cyprinids. Fish density, determined from gill netting, was highest on the largest and shallowest reservoir. Over two decades, ospreys shifted their relative spatial use of the upper Missouri River such that reservoirs were occupied first and the free-flowing river section was occupied last. The degree to which presence of conspecifics, distribution of nest trees and prey, and dispersal affected settlement patterns probably varied by spatial scale.

--Adult Bald Eagles (Haliaeetus leucocephalus) (N = 15) wintering in the San Luis Valley (SLV), Colorado were radio-tagged with conventional tail-mounted transmitters between 1 January-18 March 1980 and 1981 to determine migration patterns and breeding areas. Migrating eagles were fbllowed primarily in a single vehicle with two trackers. In 1980, radio-tagged eagles (N = 4) left the wintering grounds within a 15-d span in March but departures in 1981 (N = 7) ranged fi:om mid-February to early April. Eagles initiated migration on days with higher temperature ranges, more clouds, and higher winds than other days during winter or spring. Subsequent travel paralleled the northward movement of the 2øC isotherm both temporally and spatially. Locations and pathways of migrating eagles were similar in both 1980 and 1981. All four eagles located on their summer range were within 102 km of each other in northeastern Saskatchewan and northwestern Manitoba. Mean distance fi:om the SLV wintering area to breeding or summer areas of Bald Eagles was 2019 km. Adult Bald Eagles apparently migrated alone in spring with mated males leaving first. Migration flights began between 1015-1045 H MST and ended between 1715-1745 H. Mean daily movement was 180 km. Migration flight speeds averaged about 50 km/hr. Altitude of flight ranged fi:om 30-4572 m above ground level (AGL), but most often was between 1500-3050 m.

Golden Eagles (Aquila chrysaetos) were banded as nestlings, migrants, wintering birds, and resident breeders in three states of the U.S. Rocky Mountain West between June 1973 and January 1999. To January 2000, 6.2% of 325 eagles banded had been encountered as dead or injured birds or live captures. Median age of all encounters was 2.25 yr. Sex ratio of Golden Eagles encountered was not different from sex ratio at banding. Eagles banded as migrants were encountered less frequently than those banded as nestlings, residents, or wintering eagles. Cumulative exponential distribution analysis of recoveries (dead eagles) by age indicated 50% of banded eagles were dead by 2 yr, 7 mo, 75% by age 5 yr, 1 me, and 95% by 11 yr, 1 mo, with a maximum predicted age of 33 yr, 10 mo. Distance from banding to encounter site was <90 km for 90% of encounters, and all encounters of eagles banded as nestlings were within 200 km of their natal nest. Mean vector bearing of all encounters was 92.95degrees. Rayleigh tests for uniformity indicated encounters showed no directional bias, but only 22% of all encounters were westward. No encounters occurred on the slope of the Continental Divide opposite from banding. The largest proportion (40%) of Golden Eagles encountered died of unknown causes, and eagles less than one-year old may suffer the highest mortality rate. Considering the minimal contribution of recent nestling banding to the understanding of Golden Eagle demography and natural history, conservation and management of the species may be better served by focusing on more productive methods of research (color-marking, radio-tagging) rather than simply banding nestlings.

Of 233 Ferruginous Hawks (Buteo regalis) banded as nestlings in three study areas of Montana over 16 years, 15 (6.4%) were recovered. Recovery rate increased with duration of study and cumulative number banded. Mean age at recovery, for all Ferruginous Hawks banded in Montana was 390 days. Analysis indicated 50% of banded hawks were dead by between 0.35 and 0.70 yr and 95% were dead by between 1.5 and 3 yr of age. Survival estimated at one year was higher if hawks recovered by radio-tracking were excluded. Mean distance from the natal nest of all recoveries of Ferruginous Hawks banded in Montana was 824 km, Eight recoveries were of recently fledged hawks <1 km fr om the natal nest, but tftr remainder were recovered greater than or equal to 1500 km from the natal nest. Recoveries that were outside natal 10-minute blocks (n = 7) occurred in northern Mexico, central New Mexico, southern California, and Texas; most (86%) were southeast of the natal nest. Six hawks died front unknown causes. five from predation, two from conflicts with power lines or towers, and two from injuries. Predation occurred more often within than outside natal 10-minute blocks. Recovery locations suggested that breeding populations of Ferruginous Hawks remain segregated during winter. Mortality from electrocution and collision may be important for some populations, especially those that winter in populated areas of California and Mexico.

Several techniques are available for areal analysis of animal locations but few are applicable to those that use linear (i.e., riparian) habitats. Bald Eagles (Haliaeetus leucocephalus) often are associated with rivers and concentrate perch sites near shorelines. Distribution of cumulative proportion of perches by distance from most recently active nest sites determined by radio tracking were used to compare spatial use among five adult Bald Eagles breeding along the Snake River, Wyoming. Spatial Use Indicators (SUIs) were developed from logistic regression parameters in attempts to: (1) understand and model underlying processes from which the data may have emerged, (2) compare with simple descriptive statistical techniques to evaluate utility for presenting a clear, accurate representation of spatial use differences among eagles, and, (3) relate measures of eagle spatial rise with long-term productivity of breeding areas. Distance Indicator (DI) was the distance from the nest including 50% of all detected perches used by a radio-tagged eagle and was representative of the size of the range. Slope Indicator (SI) was the slope of the fitted logistic regression curve at the DI (inflection point). SI was an indicator of linear dispersion of perch sites within the breeding area. Bald Eagles associated with more productive (>0.77 young per occupied nest over 11 years) breeding areas perched closer to nest sites (similar DIs) than eagles of their respective gender in a breeding areas of low productivity (<0.77 voting per occupied nest). Male Bald Eagles in highly productive breeding areas dispersed perch sites more evenly throughout the breeding area (flat SI) than a male in a low production breeding area, while the opposite was true for females. Spatial use profiles derived from analysis of mean and confidence intervals and median and Interquartile Ranges were not as descriptive or illustrative of individual or group similarities or differences as SUIs. Logistic analysis suggested Zone 11 (primary foraging zone) limits recommended in regional Bald Eagle management plans may need to be extended to maintain performance of highly-productive pairs nesting along rivers. SUIs derived front logistic regression models of distance of locations from important habitat components may be indirect indicators of habitat quality and useful tools for describing and comparing spatial use of linear habitats of other species.

We determined the numerical and functional responses of migrant Bald Eagles (Haliaeetus leucocephalus) feeding on spawning kokanee salmon (Oncorhynchus nerka) at Hauser Reservoir, Montana from 1991–1995. Number of Bald Eagles was positively correlated with the fluctuating number of salmon carcasses during four of five years. Immigration and emigration rates were similar across years and were facilitated by several behavioral and physical characteristics of eagles: group foraging, communal roosting, and keen eyesight. Number of subadult eagles showed closer synchrony with density of salmon carcasses than did adult eagles. Eagles scavenging for salmon exhibited a Type II functional response. Handling times of scavenging eagles remained constant across the range of salmon carcass densities, whereas daily attack rates increased. Functional responses of scavenging eagles differed between age groups; adults exhibited a Type I response, whereas that of subadults could not be characterized. Handling times of scavenging adults were constant, but those of subadults increased with salmon density. Attack rates of scavenging adults increased with salmon carcass density. Consumption rates differed between age groups and among eagles using foraging modes of scavenging, stooping, and pirating, which suggests that eagles viewed live and dead salmon as alternative prey types. Bald Eagle scavenging of kokanee salmon was inversely density dependent.

Rates and timing of bird passage in the proposed Norris Hill Wind Resource Area (NHWRA) and vicinity in southwesteren Montana were investigated using two marine surveillance radars between August 1995 and August 1996. The scanning radar array displayed movements in a horizontal plane within 360 degrees while the vertical radar displayed altitudes of bir dr in and out of the NHWRA to the east and west. Radars were also used to record raptor movements within NHWRA in summer. Spatio-temporal profile of migration was determined by adjusting observed number of events by detection probability by radar, derived from point- and line-transect bird sampling techniques. Autumn migration was more protracted than vernal migration. Altitude of birds flying in and within 2 km east and west of NHWRA averaged 209 m in autumn and 388 m in spring. Higher altitudes in spring were a function of birds ascending after leaving Ennis Lake, whereas birds were descending to visit the lake in autumn. More birds passed over valleys and swales than high points. Passage rate decreased with declining barometric trend in autumn (headwinds), but the reverse was true in spring (tailwinds).

Movements and survival of immature Laid eagles (Haliacetus leucocephalus) beyond their first winter remain largely unknown, and lack of information may impede strategies for effective conservation. We analyzed encounters, sightings, and radio detections of bald eagles auxiliary marked as nestlings in the Greater Yellowstone Ecosystem (GYE) between June 1979 and July 1987 to determine movements, survival, and role of Yellowstone National Park in the ecology of CTE bald eagles. Of 344 bald eagles Landed, 17% were encountered to June 1998. Most (84%) were encounters of bald eagles >1 year old. Half of encounters were external to the GYE and occurred in 7 western states and 1 Canadian province. All sightings of color-landed bald eagles (n = 76) were of bald eagles >1 year old, and 76% occurred in the GYE. Location and timing of encounters and detections of radiotagged bald eagles indicated most (>90%) juveniles left the GYE in autumn, traveled as far west as coastal stales to winter, and returned to natal areas the following spring. Natal dispersal appeared female-biased, and bald eagles produced in the GYE recruited into breeding populations both in and out of the ecosystem. Mortality of 49 bald eagles recovered was from unknown causes (31%), electrocution or collision with power lines (20%), known or suspected poisoning (16%), and gunshot wounds (14%). Eighteen percent was distributed among 3 other causes. Recovery rates indicated Laid eagles 3-5 years old experienced the highest mortality Kaplan-Meir analysis of detections of radiotagged Laid eagles indicated first-lear survival of 87%, followed by a constant decrease in survival rate over 7 years. Survival estimates determined by radio-tracking were consistent Midi Land recovery results in illustrating low survival in 3- to 5-year-old age classes. Radiotracking of immature bald eagles suggested habitat in Yellowstone National Park was important in promoting survival of eventual recruits to the GYE population.

The connection between bald eagles (Haliaeetus leucocephalus) and the consumption of waterfowl, lead shotshell pellet ingestion, and subsequent lead exposure is well documented in the United States and is presumed also to be widespread in Canada. We compared blood lead concentrations in samples from bald eagles ranging in age from 0.5- to 1.5-yr-old at Galloway Bay, Saskatchewan, Canada (n = 97) during October–November, 1992–95 and Hauser Lake, Montana, USA (n = 81) during October-December, 1990–94, within the Great Plains region of North America. Abundant prey are available in the form of hunter-injured waterfowl in Saskatchewan and spawning salmon in Montana; both areas attract large numbers of mid-continent bald eagles during fall migration. Blood lead concentrations suggestive of recent lead exposure (>0.201 μg/ml) were found in 32% and 8% of eagles at Hauser Lake and Galloway Bay, respectively, when samples from each study area were analyzed independently at two laboratories. To determine if this difference was an artifact of interlaboratory variation, we determined a correction factor by reanalyzing 14 Saskatchewan blood samples at each laboratory and predicted blood lead concentrations from Hauser Lake had the samples been analyzed at the Canadian laboratory. Adjusted blood lead concentrations of samples from Hauser Lake indicated that 21% of eagles were recently exposed to lead, a proportion not significantly different from the proportion of the same exposure category at Galloway Bay. Our data do not support the supposition that a large proportion of bald eagles feeding on waterfowl in areas of high hunting pressure will be exposed to lead via consumption of lead shotshell pellets in waterfowl.