We studied habitat use and spatial distribution of Common Buzzards (Buteo buteo) in Schleswig–Holstein, northern Germany during the autumn of 2000, to assess the raptors' territoriality and its consequences for their use of space. For this purpose, we performed point counts covering an area of 20 km² during each of 20 continuous days and recorded 1537 observations of Common Buzzards and 109 of Rough-legged Hawks (Buteo lagopus). Applying multivariate Poisson regression combined with randomization tests, we detected that Common Buzzards showed a preference for areas with a larger distance from nesting sites of the previous spring (P  =  0.019; n  =  290 grid units of 250 × 250 m in all three cases), a high density of vole holes (P < 0.001), and a low density of perch-sites (P  =  0.005). These preferences regarding vole holes and perches were also valid when only grid units far from the nesting sites were considered. Indirectly, the buzzards were also affected by the amount of grassland and by the amount of dry land, as these parameters were strongly related to vole-hole density. The distributions of the sympatric wintering species Rough-legged Hawk and Common Buzzard did not affect each other. Our study indicated that territorial sedentary breeding pairs displaced nonbreeders and wintering birds into suboptimal habitats, and it offers valuable clues on the constraints for Common Buzzards in areas where they occur in high abundance during late autumn and winter.

Release methods used in species restoration can affect the success of establishment and survival of released animals. We evaluated the effect of age at release and sex on the length of the dependence period of hacked captive-bred juvenile Harpy Eagles (Harpia harpyja). Between 2002 and 2007, we released 34 (19 males and 15 females) young eagles in Panama and Belize. To test the effect of age, these eagles were divided into two age classes: younger age class 1 (5–7 mo old) and older age class 2 (18–22 mo old). Survival (hacking success) was lower for the younger release age (70%) compared to the older release age (100%; Z  =  −2.05, P  =  0.040). This difference in hacking success was attributed to the extended period of dependence on provisioned food by the younger (18.9 ± 1.3 mo [SE]) compared to older eagles (1.5 ± 0.8 mo). Between-sex comparisons showed that the average length of the dependence period was longer for males of age class 1 (males  =  21.8 mo vs. females  =  14.3 mo) and for females of age class 2 (females  =  2.7 mo vs. males  =  0 mo). Cox regression models indicated that the interaction of age at release and sex had a significant effect on the dependence period, and that age at release was the most influential variable. Eagles released at 18 mo or older showed increased survival and shorter dependence periods. Hacking can be used to successfully release captive-bred Harpy Eagles into the wild, but this technique was more efficient when delayed from fledging age (when falconers traditionally hack falcons) to nearer the Harpy Eagle's age of independence.

Bald Eagles (Haliaeetus leucocephalus) were one of the upper-trophic-level avian predators on the Channel Islands, California, prior to their extirpation by 1960 caused in part by large amounts of DDT discharged into the Southern California Bight. From 2002 to 2006, 61 Bald Eagles were reintroduced onto the northern Channel Islands, as part of a 5-yr feasibility study conducted under the auspices of the Montrose Settlement Restoration Program. In December 2005, a yearling Bald Eagle female was found on Santa Rosa Island with a broken wing and elevated lead levels in her blood of 52.2 ug/dl (0.522 ppm). This incident raised concerns that lead poisoning could be a potential threat to the restoration effort and prompted further investigation. Femurs from five female and two male Bald Eagles reintroduced to the northern Channel Islands were collected postmortem for analyses of lead and other metals. Lead levels detected in femurs of these birds ranged from 0.2 to 55.0 ppm (dry weight). Lead levels in liver were also determined for two of the seven Bald Eagles. Analysis of Bald Eagle movement data from satellite telemetry transmitters suggested that eagles that spent the most time on Santa Rosa Island had the highest lead levels. The results of this study suggested that spent ammunition containing lead found in carrion (offal and entire carcasses) from deer and elk hunting on Santa Rosa Island may have been a primary source of contamination. The on-island hunt program converted to nontoxic bullets in 2007 and ended in late 2011.

Characterizing the migration strategies of Northern Saw-whet Owls (Aegolius acadicus) has proved difficult due to variation in movement patterns within and among regions. Such variation underscores the need for information from sites throughout the species' range. To elucidate regional patterns in Northern Saw-whet Owl migration ecology, I studied migration in northern Montana from 2001–06, banding a total of 668 owls between 30 August and 31 October. Capture rates varied greatly among years, as did age ratios. Capture rates peaked between mid-September and early October. Weather variables did not have detectable effects on migration magnitude, but capture rates decreased approximately 2% for every 10% increase in moon illumination. Two owls originally banded in Alberta were captured at my banding site during this study. Additionally, two owls banded during this study were encountered elsewhere: one found dead in southern Montana and the other recaptured in Massachusetts, approximately 3322 km east of my study site. Results were consistent with the hypothesis that high rates of breeding dispersal and density-dependent migratory responses yield annual, latitudinal migrations that vary in magnitude and have a nomadic component.

We studied reversed sexual dimorphism (RSD) and foraging behavior of Barn Owls (Tyto alba). Bill length, tarsus length, wing chord, tail length, and mass of Barn Owls showed RSD. Mass of the prey items brought by the males was significantly less than that brought by females, which may be attributed to the positive correlation between size of the owl and prey mass. However, male owls had a significantly higher frequency of visits with prey than did females. There was relatively little overlap in the species and mass of prey captured by males and females, suggesting that food-niche partitioning between the sexes may exist, possibly to reduce intersexual food competition. Further, because these differences were also observed between the male and female owls within each pair, our findings support reproductive role division as a possible explanation for RSD in Barn Owls.

Little is known about the habitat and ecology of suburban Barred Owls (Strix varia), a species sometimes considered the nocturnal equivalent of Red-shouldered Hawks (Buteo lineatus). We compared nesting habitat of Barred Owls to that of Red-shouldered Hawks nesting in suburban and urban areas, in and near the city of Cincinnati, Ohio, to determine whether any features distinguished owl nest sites from hawk nest sites. We characterized habitat and land-cover metrics in circular plots of 100 ha and 15 ha, centered on the owl and hawk nests, using ATtiILa software operating within a GIS environment. For the 100-ha plots, the primary cover type in the plots surrounding nests of both species was forest, 41.4 ± 3.4% for Barred Owl plots and 45.9 ± 3.4% for Red-shouldered Hawk plots, followed by low-density residential land: 29.8 ± 4.8% of the Barred Owl plots and 29.3 ± 3.7% of the Red-shouldered Hawk plots. Pasture composed <15% of the plot area for both species and the remainder of the cover types contributed even less. Values of land-cover percentages and metrics did not differ between the species (P > 0.05), for either the large plots or the small (15-ha) plots. Using stepwise binary logit regression analysis, we found that no variables discriminated owl plots from hawk plots. We concluded, based on our methodology, that habitat of suburban Barred Owls differed little from habitat of suburban Red-shouldered Hawks in southwestern Ohio.

Raptors are highly susceptible to poisoning by anticholinesterase drugs and pesticides, such as organophosphates and carbamates, due to their carnivorous and/or insectivorous diets. Measurement of plasma cholinesterase inhibition is a proxy indicator of exposure to these agents; however, prior knowledge of the normal plasma cholinesterase activity of healthy birds is required for interpretation of results. Such normal values have not yet been established for most species of neotropical raptors. We collected blood samples from 133 raptors, including eleven species of Falconiformes (n  =  45) and seven species of Strigiformes (n  =  88). The birds had no clinical signs or history of possible exposure to anticholinesterase drugs and were housed in rehabilitation centers (free-ranging animals) and zoos (captive animals) in the state of São Paulo, southeastern Brazil. We found that plasma cholinesterase activity, as measured by the Ellman method, had a logarithmic distribution with a median of 0.58 µmols/mL for Falconiformes (quartiles: Q1  =  0.43; Q₃  =  0.73) and 0.96 µmols/mL for Strigiformes (Q₁  =  0.78; Q₃  =  1.25). There were no significant differences between sex or age classes within Falconiformes or Strigiformes. Captive Strigiformes in zoos had lower plasma cholinesterase activity values than birds housed in the rehabilitation centers, a pattern that did not occur in Falconiformes. These results provide reference values of plasma cholinesterase activity for the future interpretation of suspected pesticide poisoning in neotropical raptors.