Resumen El empetrolado de las aves puede tener consecuencias importantes a nivel individual y poblacional. Aunque la mayoria de los ejemplos publicados sobre empetrolado se refieren a la exposicion a fuentes antropicas de hidrocarburos, el empetrolado puede ocurrir naturalmente. Describimos cuatro casos de empetrolado natural de siete pollos de Aquila chrysaetos asi como nuestra intervencion para mitigarlo. En todos los casos, el aceite en estas aves provino casi seguro de sus presas, en su mayoria ardillas terrestres (Otospermophilus beecheyi), aportadas por aguilas adultas en cantidades mayores de las que los polluelos podian consumir. Algunos pollos solo fueron empetrolados levemente. Otros fueron empetrolados tanto que la funcion de las plumas se vio comprometida a un nivel en el que, sin nuestra intervencion, la supervivencia de estos pollos de aguila seguramente hubiera sido afectada. Hasta donde sabemos, este es el primer informe publicado sobre empetrolado de rapaces como consecuencia de un sobre ...

Raptors are exposed to a wide variety of human-related mortality agents, and yet population-level effects are rarely quantified. Doing so requires modeling vital rates in the context of species life-history, behavior, and population dynamics theory. In this paper, we explore the details of such an analysis by focusing on the demography of a resident, tree-nesting population of golden eagles (Aquila chrysaetos) in the vicinity of an extensive (142 km2) windfarm in California. During 1994-2000, we tracked the fates of >250 radio-marked individuals of four life-stages and conducted five annual surveys of territory occupancy and reproduction. Collisions with wind turbines accounted for 41% of 88 uncensored fatalities, most of which were subadults and nonbreeding adults (floaters). A consistent overall male preponderance in the population meant that females were the limiting sex in this territorial, monogamous species. Estimates of potential population growth rate and associated variance indicated a stable breeding population, but one for which any further decrease in vital rates would require immigrant floaters to fill territory vacancies. Occupancy surveys 5 and 13 years later (2005 and 2013) showed that the nesting population remained intact, and no upward trend was apparent in the proportion of subadult eagles as pair members, a condition that would have suggested a deficit of adult replacements. However, the number of golden eagle pairs required to support windfarm mortality was large. We estimated that the entire annual reproductive output of 216-255 breeding pairs would have been necessary to support published estimates of 55-65 turbine blade-strike fatalities per year. Although the vital rates forming the basis for these calculations may have changed since the data were collected, our approach should be useful for gaining a clearer understanding of how anthropogenic mortality affects the health of raptor populations, particularly those species with delayed maturity and naturally low reproductive rates.

Abstract During 1987–89, we placed VHF transmitters and colored identification bands on 15 nestling Bald Eagles (Haliaeetus leucocephalus) in central Arizona to determine the direction and extent of their post-fledging migration. Thirteen of the juveniles fledged successfully, and one transmitter failed; 11 eagles survived the post-fledging, premigration period which ranged from 18 to 65 d (mean  =  44 d). One eagle was lost by trackers after departure, but 10 monitored eagles traveled north from 925 km to 1955 km before stopping for extended periods or until weather prevented further tracking. Habitats varied among stopping locations and included interior reservoirs and lakes, open ranchland, and the Pacific marine coast. Food at inland destinations included spawning fish (cutthroat trout [Salmo clarki]) and fish carrion (common carp [Cyprinus carpio] and white suckers [Catostomus commersoni]). At least nine of 13 fledged juveniles survived ≥1 yr (69%), and a minimum of six (46%) survived to breeding age.

We studied food habits, mechanisms of prey acquisition, and the effects of reservoir drawdown and fisheries management in a population of Bald Eagles (Haliaeetus leucocephalus) nesting on Shasta (Lake) Reservoir, a large impoundment in northern California used intensively for irrigation and recreation. Prey deliveries at seven nests were mostly bass (Micropterus sp., 55% of total prey biomass) and salmonids (14%), and all principal fish prey species were either introduced or regularly stocked. Carrion and moribund fish, mostly bass, accounted for > 75% of successful foraging attempts. Fish mortality was related to spawning stress, disease, and catch-and-release angling; fish fatalities associated with bass fishing provided carrion throughout the breeding season. The proportions of fish species in the eagles' diet, as measured by prey deliveries to the nest, were positively correlated with those found in live-fish sampling and carrion surveys; all were predominantly bass. Benefits associated with seasonal and long-term reservoir drawdown included exposing spawning and foraging fish to eagle predation, and the likely release of nutrients and food for rapid fish growth upon re-inundation. Probable disadvantages of extended drawdown included loss of eagle foraging habitat and reductions in the standing crop of fish, likely resulting in competition among eagle pairs. Bald Eagle productivity was at or above average during the 2-yr study, a relatively wet period following along drought and associated low pool levels, and we found a positive relationship between historic spring reservoir levels and Bald Eagle productivity from 1979-1999. Effects of fish introductions on trophic relationships and species composition warrant careful examination of eagle foraging requirements; however, past and present fisheries management appears to be currently benefiting the opportunistic eagles.

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 Canada's 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.

We studied the breeding success of resident Bald Eagles (Haliaeetus leucocephalus) over a 20-year period along the Pit River drainage in northern California. In 258 nesting attempts at 10 intensively studied nesting territories, 0.31 to 1.65 young were produced per year per occupied territory (mean = 0.97), with average nesting success of 62%. Nineteen individually banded breeding adult Bald Eagles produced from zero to 36 young during their lifetimes, and birds remained on their territories for 1–16 years following capture as adults. We calculated a 90% annual survival rate for breeding adults from our sample of 19 birds, with longevity of one banded eagle at 22 years. Eagles that bred on a territory for a greater number of years did not produce a greater number of young annually on average than other breeding birds. Larger males, as evidenced by body mass at capture, produced significantly more young over their lifetimes than smaller males. This same relationship did not hold for females, however. Seven banded pairs of adults remained together on their territories for 3–15 years. Reproduction decreased significantly following replacement of a breeding adult on a territory, and this effect continued for 2–3 years following replacement.

We trapped and translocated golden eagles (Aquila chrysaetos) from the Channel Islands off the southern California coast between 1999 and 2003 in an ongoing effort to mitigate a catastrophic decline in three subspecies of island fox (Urocyon littoralis). As of August 2003, we had removed 31 (70%) of 44 known eagles from Santa Cruz and Santa Rosa Islands. Translocated eagles were released in areas of suitable habitat in northern California from 275–880 km from the islands. Eaglets removed from nests were either fostered into mainland golden eagle nests or hacked into the wild. Eleven of the released eagles (seven adults, three subadults, one juvenile) were tracked with combination satellite and conventional VHF transmitters to determine if they would return to the islands. The satellite transmitters operated for an average of 13.6 months (range 0–28). We obtained 1,568 satellite locations of class 3, 2, or 1 (est. accuracy of <150 – <1,000 m). Locations were plotted and analyzed with the geographic information system ArcGIS 8.0. Released birds ranged over areas of 1,366–256,413 km. The most proximal location obtained was 304 km NNE of Santa Cruz Island. Sensor data suggested that five eagles (45%) shed their transmitters or died within 1–7 months. Six birds were still alive and wearing their transmitters when transmissions ceased (5–28 months post-release). None of the radioed eagles returned to the islands during tracking and no banded golden eagles have subsequently been observed on the islands. Since the onset of eagle removal efforts, annual island fox survivorship on Santa Cruz Island has risen to near pre-decline levels. We conclude that translocation of golden eagles is an effective non-lethal method of reducing the island golden eagle population and their potential impact on island fox recovery.

ABSTRACT.---Inland nesting Bald Eagles (Haliaeetus leucocephalus) in northern California preyed on both native and introduced freshwater fish species, primarily brown bullhead (Ameiurus nebulosus), Sacramen- to sucker (Cat0st0mus occidentalis), common carp (Cyprinus carpio) and tui chub (Gila bicolor). At most locations, eagles ate mainly fish; however, birds, principally American Coots (Fulica americana) and Mal- lards (Anas platyrhynchos), were more important than fish at sites isolated from large rivers. Fish species taken by eagles varied between major drainages: Sacramento sucker were most common,in eagle diets