Alan R. Harmata

Movements and survival of bald eagles banded in the greater yellowstone ecosystem

Movements and survival of immature bald eagles (Haliaeetus 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 1997 to determine movements, survival, and role of Yellowstone National Park in the ecology of GYE bald eagles. Of 344 bald eagles banded, 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-banded 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 states 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 bald eagles 3-5 years old experienced the highest mortality. Kaplan-Meir analysis of detections of radiotagged bald eagles indicated first-year survival of 87%, followed by a constant decrease in survival rate over 7 years. Survival estimates determined by radiotracking were consistent with band 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.

NUMERICAL AND FUNCTIONAL RESPONSES OF MIGRANT BALD EAGLES EXPLOITING A SEASONALLY CONCENTRATED FOOD SOURCE

Abstract 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.

A COMPARISON OF BLOOD LEAD LEVELS IN BALD EAGLES FROM TWO REGIONS ON THE GREAT PLAINS OF NORTH AMERICA

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.

LEAD, MERCURY, SELENIUM, AND OTHER TRACE ELEMENTS IN TISSUES OF GOLDEN EAGLES FROM SOUTHWESTERN MONTANA, USA

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).

Encounters of Golden Eagles banded in the Rocky Mountain West

Abstract 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 mo, 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 92.95°. 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.

Natal Dispersal Distance of Bald and Golden Eagles Originating in the Coterminous United States as Inferred from Band Encounters

Abstract We reviewed band encounter data for Bald Eagles (Haliaeetus leucocephalus) and Golden Eagles (Aquila chrysaetos) 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. DISTANCIA DE DISPERSIóN NATAL DE HALIAEETUS LEUCOCEPHALUS Y AQUILA CHRYSAETOS ORIGINADA EN ESTADOS UNIDOS CONTIGUO INFERIDA A PARTIR DE ENCUENTROS DE ANILLOS Examinamos datos de encuentros de anillos de Haliaeetus leucocephalus y Aquila chrysaetos para estimar las distancias de dispersión natal para ambas especies en Estados Unidos contiguo (EEUU). Filtramos datos de recuperación de anillos para enfocarnos en individuos anillados cuando eran pichones, encontrados a edades suficientes como para estar reproduciéndose y encontrados en épocas del año cuando pueden estar en o cerca de sitios de reproducción o de sitios de prospección de reproducción. Nuestro grupo de datos final incluyó 96 individuos de A. chrysaetos y 878 individuos de H. leucocephalus. Las distancias entre los sitios de anillado y los de encuentro subsecuente para ambas especies presentaron una distribución log-normal. Utilizamos tanto métodos de análisis tradicionales como bayesianos y obtuvimos resultados similares con ambos métodos. El análisis bayesiano de los datos de anillado sugiere una distancia de dispersión natal mediana de 69.2 (95% de intervalo de densidad mayor [IDM]  =  63.5–73.1) km para H. leucocephalus y 46.4 (IDM  =  36.0–55.2) km para A. chrysaetos. La distancia de dispersión natal mediana para hembras de H. leucocephalus fue 78.3 (IDM  =  35.4–128.6) km más grande que para los machos; faltaron datos suficientes para analizar la dispersión natal por sexos para A. chrysaetos. La distancia de dispersión natal mediana de H. leucocephalus no difirió entre ocho poblaciones regionales, pero se encontró evidencia de una tendencia hacia un incremento de la distancia de dispersión natal de este a oeste en EEUU contiguo. Nuestros resultados son compatibles con los datos de dispersión natal en la literatura para ambas especies. El Servicio de Pesca y Vida Silvestre de EEUU usa la distancia de dispersión natal estimada para H. leucocephalus para determinar una de las escalas geográficas en la cual se evalúan los efectos de los permisos que autorizan la colecta (remoción del estado silvestre). Nuestros análisis sugieren que la elección del valor de dispersión natal en el rango del 50°–90° cuartil de la distribución como un área de modelado o de evaluación para ambas especies de águila es razonable. Para A. chrysaetos, este rango es de 46–175 km y para H. leucocephalus es de 69–346 km.

MOVEMENTS AND MORTALITY OF FERRUGINOUS HAWKS BANDED IN MONTANA

Abstract 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 from the natal nest, but the remainder were recovered ≥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 from 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.

Environmental Contaminants in Nestling Bald Eagles Produced in Montana and Wyoming

Abstract 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 (  =  0.37 ± 0.22 ppm) had higher blood mercury concentrations than nestlings from Montana (  =  0.22 ± 0.17 ppm; t31  =  3.151, P  =  0.015). In Montana, nestlings sampled on Yellowstone River tributaries had lower blood mercury concentrations (  =  0.12 ± 0.10 ppm) than nestlings from the main stem of the Yellowstone River (  =  0.28 ± 0.21 ppm) and Wyoming (  =  0.37 ± 0.22 ppm; F2,32  =  12.439, P < 0.001). Blood levels of mercury and selenium were positively correlated (rS  =  0.281, n  =  64, P  =  0.024). Lead (  =  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 (  =  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. CONTAMINANTES AMBIENTALES EN POLLUELOS DE HALIAEETUS LEUCOCEPHALUS PRODUCIDOS EN MONTANA Y WYOMING Las especies piscívoras de un nivel trófico alto, como Haliaeetus leucocephalus, pueden estar en riesgo de exposición a contaminantes ambientales provenientes de plantas de generación eléctrica a carbón y pozos de metano de mantos carboníferos en el oeste de los Estados Unidos. Colectamos 64 muestras de sangre de pichones de H. leucocephalus en el sudeste de Montana y noroeste de Wyoming durante el 2007 y 2008 para análisis de metales pesados, oligoelementos y compuestos organoclorados. Se detectó mercurio en todas las muestras de sangre, el cual promedió (±DE) 0.28 ± 0.20 ppm. La mayoría de los pichones (82.8%) presentó concentraciones cercanas a los niveles de fondo esperados, pero 7.8% tuvo niveles elevados (>0.7 ppm) de mercurio. Los pichones de Wyoming (  =  0.37 ± 0.22 ppm) presentaron concentraciones de mercurio en sangre mayores que las de los pichones de Montana (  =  0.22 ± 0.17 ppm; t31  =  3.151, P  =  0.015). En Montana, los pichones muestreados en tributarios del Río Yellowstone presentaron concentraciones de mercurio en sangre menores (  =  0.12 ± 0.10 ppm) que las de los pichones del cauce principal del Río Yellowstone (  =  0.28 ± 0.21 ppm) y Wyoming (  =  0.37 ± 0.22 ppm; F2,32  =  12.439, P < 0.001). Los niveles en sangre de mercurio y selenio estuvieron positivamente correlacionados (rS  =  0.281, n  =  64, P  =  0.024). Se detectó plomo (  =  0.07 ± 0.08 ppm) en 81.3% de los pichones, pero sólo 11.5% de ellos fueron considerados como por encima de los niveles de fondo. El compuesto organoclorado p,p′-DDE (  =  0.003 ± 0.003 ppm) fue detectado en 69.6% de los pichones muestreados. Comparado con estudios previos en la región, la contaminación por mercurio se ha extendido, mientras que la prevalencia de contaminación por plomo fue similar a la del pasado. Basados en este estudio, sugerimos que algunos polluelos de H. leucocephalus pueden estar experimentando efectos adversos por contaminación con mercurio y recomendamos que se establezcan monitoreos adicionales mientras las plantas de generación eléctrica a carbón y la industria de pozos de metano de mantos carboníferos continúen su expansión.

Retention, Effect, and Utility of Tail-mounted Satellite-tracked Transmitters on Golden Eagles

Abstract 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 PTT 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.