We used radiotelemetry to study space use and habitat selection of 16 Northern Spotted Owls (Strix occidentalis caurina) on the eastern slope of the Cascade Mountains, Washington, U.S.A., in 1989–1990. We used a geographical information system (GIS) and aerial photo interpretation of digital orthophotos to assign owl locations a value for vegetation type, topographic position, amount of edge, and distance to water. We compared owl relocations and random locations within 95% fixed kernel (FK) home ranges to determine each owl's selection of cover types, using logistic regression and generalized estimating equations (GEE) to estimate an exponential resource selection function likelihood. Minimum convex polygon (MCP) home ranges (SE) averaged 2858 ha (712 ha) for males and 1883 ha (249 ha) for females. Individual 95% FK home ranges averaged 1980 ha (229 ha) for males and 1649 ha (163 ha) for females. Pair home ranges averaged 3419 ha (826 ha) for MCP and 2427 ha (243 ha) for 95% FK. Nonbreeding season home ranges averaged approximately 3.5 times larger than breeding season home ranges for both males and females. Our best habitat model indicated that owls selected closed-canopy forests with a component of large (≥50 cm dbh) trees for roosting and foraging. In a given cover type, owls foraged lower on the slope. Management circles centered on nest areas—commonly used as a surrogate for home ranges—can be relatively poor representations of actual ranges used by pairs. However, an alternative for managing Spotted Owl home ranges is not readily available. Maintaining sufficient closed-canopy forest to provide habitat for Spotted Owls in the dry, fire-prone forests on the eastern slope of the Washington Cascades will be a challenge because forestry methods used to reduce the risk or severity of fire generally reduce the prevalence of structural features that characterize good Spotted Owl habitat.

Competitive interactions with Barred Owls (Strix varia) are an important factor contributing to the decline of the Northern Spotted Owl (Strix occidentalis caurina) population. Understanding the degree of similarity in fine-scale habitat associations for Spotted Owls and Barred Owls will help land managers evaluate whether there are specific vegetation conditions that could favor Spotted Owls over Barred Owls. From March 2004 to September 2006, I tracked 14 radio-tagged Barred Owls in the Okanogan-Wenatchee National Forest in the eastern Cascade Range, Washington. I analyzed forest structure characteristics from 170 plots sampled within areas used by the radio-tagged owls. I identified three forest types present within the Barred Owl home ranges, including: (1) open ponderosa pine (Pinus ponderosa), (2) simple-structure Douglas-fir (Pseudotsuga menziesii), and (3) complex-structure grand fir (Abies grandis). I compared individual forest structure characteristics and the three forest types to the intensity of Barred Owl use based on repeated measures of seasonal utilization distribution values at each plot using hierarchical mixed-effects models. Intensity of Barred Owl use during the breeding season was higher in areas with greater abundance of grand fir trees, taller and more diverse tree heights, more total trees per ha, more trees 12.7–22.9 cm dbh, more tree canopy >4.9 m, and less ground-cover vegetation <0.6 m. During the nonbreeding season, intensity of Barred Owl use was higher in areas with more trees 12.7–22.9 cm dbh, more total trees per ha, gentle slopes, and increased tree species diversity. Barred Owls used the structurally diverse grand fir forest type more intensively than the other two types during the breeding season. Intensity of use did not differ across the types during the nonbreeding season. Forest structure characteristics used by Barred Owls in this study were within the range of conditions reported to be used by Spotted Owls in the eastern Cascade Range.

Urban ecosystems are attractive to several raptor species, including the Mississippi Kite (Ictinia mississippiensis). To better understand the niche filled by urban-nesting Mississippi Kites, we observed nesting kites at 10 nests for a total of 269 hr during the breeding seasons of 2010 and 2011. We assessed prey delivery rates and prey use within and between years, evaluated the influences of nestling age, time of day, day of year, and local atmospheric conditions on delivery rates, and examined provisioning rates by male and female kites. A 62% decrease in the prey delivery rate, measured by the number of prey deliveries, from 2010 to 2011 was likely attributable to extreme heat and drought during the 2011 breeding season. However, total biomass of identified deliveries increased 38.9% in 2011 due to an increase in the percentage of avian prey (from 1% to 16% of identified deliveries). We suspect that differences in weather conditions between years influenced the type of prey delivered, and our modeling efforts indicated that year, nestling age, time of day, and temperature best explained the number of prey deliveries made per hour. On average, females delivered more prey items than males, but variability among nests suggested additional factors may influence parental effort. Our results suggest that Mississippi Kites exhibit prey switching under differing conditions.

There have been no detailed studies of predator or non-predator causes of mortality and failure at nests of the Red-shouldered Hawk (Buteo lineatus), and identification of such causes has been largely speculative. There is ample information about rates of nest success, defined as the fledging of ≥1 nestling from a nest, but this measure of reproductive rate is limited in its scope. Fledging success, measured by quantifying total nestlings lost or fledged is a more informative assessment of reproductive success, but is not often reported. We used video monitoring of suburban Red-shouldered Hawk nests to identify causes of mortality or failure. Eight of 25 nests failed completely (32%), and 17 were successful (68%). However, nine of the 17 successful nests experienced some nestling mortality, and the fledging success of individual nestlings (n  =  67) was only 58%, as 28 nestlings (42%) died before fledging. Causes of mortality or nest failure included depredation of an incubating female parent at one nest and of nestlings at multiple nests by Great Horned Owls (Bubo virginianus), depredation of nestlings by raccoons (Procyon lotor), disturbance by eastern gray squirrels (Sciurus carolinensis), unexplained disappearance of female parents, starvation of nestlings, and nestlings falling from the nest. These results provide a thorough and accurate account of reproductive success, and valuable identification of predator and non-predator causes of nestling mortality or nest failure throughout the nesting period.

We examined factors that potentially influenced reproductive success in Ferruginous Hawks (Buteo regalis) in the Uintah Basin, Utah, and determined whether oil and gas well development was one of those factors. For three breeding seasons (2002–2004), we measured the number of nestlings, fledglings, and dispersed young that were produced by pairs of Ferruginous Hawks nesting within 2365 km² managed by the Bureau of Land Management. We hypothesized that reproductive success would be influenced by nesting substrate, abundance of prey, distance to the closest occupied raptor nest, and distance to the closest active well. Although the Uintah Basin experienced a drought during our entire study, reproductive success was within the range of estimates reported in other studies in the Intermountain West. Each nesting pair produced an average of 1.9 nestlings, 1.3 fledglings, and 0.9 dispersed young. During our study, 17 nestlings and 14 fledglings died; 55% were due to avian predators, 16% to mammalian predators, 10% to unknown predators, 16% to natural causes, and 3% to unknown causes. Avian depredation may have resulted from increased competition among avian predators for scarce prey resources, or from increased use of juvenile Ferruginous Hawks as an alternative prey source by Golden Eagles (Aquila chrysaetos) in years of low lagomorph abundance. Our results suggest that the level of oil development that occurred during this study did not have an adverse effect on Ferruginous Hawk reproduction; the effect of a higher level of oil development was beyond the scope of this study.

Knowledge of the habitat characteristics that influence the distribution of raptors in the neotropics is vital for their conservation. I used logistic regressions (General Linear Models; GLM) to model habitat distribution for eleven raptor species occurring in the Cerros de Amotape National Park, the Tumbes National Reserve, and surrounding areas in northwestern Peru. Between May and December 2008 and 2009, raptors were surveyed along transects, and associated habitat data collected in 70 randomly allocated 1-km² plots. Ten habitat variables were selected for modelling. Spatial autocorrelation in the distribution of species was measured through Moran's I and later habitat models were ranked using Akaike's Information Criterion corrected for small sample sizes (AICc). The most important variables that influenced the presence of species included the percentage of vegetation cover at different strata and elevation. The presence of the tree species, ceibo (Ceiba trichistrandra) and guasima (Guazuma ulmifolia), were also important. The percentage of vegetation cover from 5–15 m appeared in all models for Turkey Vulture (Cathartes aura), Crane Hawk (Geranospiza caerulescens), Great Black Hawk (Buteogallus urubitinga), and Harris's Hawk (Parabuteo unicinctus). These findings suggest that vertical structure of forested areas is of particular importance for raptors at the study site, including those of conservation concern. I recommend that forested areas north of the Cerros de Amotape National Park and close to Ecuador should be protected.

I studied breeding ecology of White-rumped Vultures (Gyps bengalensis) in Himachal Pradesh, northern India, 2009–2012. Twenty-four breeding colonies of White-rumped Vultures were found, mainly in the Shahpur, Nurpur, and Kangra regions of Kangra District. In 2011–2012, the colonies contained a total of 102 nests, at which 81 pairs bred successfully. Nest success increased slightly from 56.1% in 2009–2010 to 79.4% in 2011–2012. All the nests of White-rumped Vultures were built in pine trees (Pinus roxburghii), at an average height of 15.4 m. In 2011–2012, approximately 65% of the nests were newly built, possibly indicating a high percentage of intra-colony movements. The number of adult and immature birds counted at the nesting colonies during the breeding season ranged from 13.3–27.3 individuals/colony; the ratio of immatures/adults varied from 0.44–0.97. Disturbance due to human activity and roads is a cause of concern for most of the breeding sites of White-rumped Vultures in Himachal Pradesh.

Most known fatalities for both Bald Eagles (Haliaeetus leucocephalus) and Golden Eagles (Aquila chrysaetos) are associated with humans (e.g., collisions with vehicles and artificial structures). Notably, the risk of collisions between eagles and aircraft is an increasing problem at civil airports and military airfields. Of the 234 eagle collisions with civil and military aircraft reported to the Federal Aviation Administration, the U.S. Air Force, and the U.S. Navy during 1990–2013, 52% caused damage to the aircraft. During this 23-yr time period, Bald Eagle–aircraft collisions increased by 2200% and Golden Eagle–aircraft collisions increased by 400%. Eagle–aircraft collisions occur primarily during daylight hours (88%) and typically within the vicinity of the airfield itself; 82.6% of the Bald Eagle–aircraft collisions and 81.0% of Golden Eagle strikes occurred when the aircraft was at or below 305 m aboveground level. Although collision with aircraft is a very minor source of mortality for Golden Eagles, increasing and expanding Bald Eagle populations will likely result in more eagle–aircraft collisions. Currently, there are few mitigation tools and techniques available to reduce eagle–aircraft collisions. Development and evaluation of effective, publically acceptable methods of reducing eagle–human conflicts represent important areas for future research.

As part of the economic and population growth of Patagonia, several dust/gravel roads crossing well preserved Andean forests are being converted into paved highways. The potential effects of these changes on forest wildlife have been little studied. The Rufous-legged Owl (Strix rufipes) was dominant among road-killed birds in our survey of a 27-km section of highway running through forests of Nahuel Huapi National Park, in Argentine Patagonia. Fatalities were not evenly distributed along the surveyed length of the road, so we investigated whether landscape features, roadside slope on both sides of the highway, demography, and/or season explained the aggregation pattern. Patterns of distribution of the road-killed owls were explained by owl abundance and age-class, time of year, and hour, and were weakly related to canopy closure; roadside slope on both sides was unrelated to abundance of fatalities. Traffic-related deaths were likely the primary cause of non-natural mortality of Rufous-legged Owls (especially for young individuals) in the study area. Examination of carcasses indicated that most owls were killed by turbulence behind large vehicles and that deaths occurred early in the night. Semitrailer trucks capable of carrying large loads, which peak in numbers between dusk and midnight, likely caused most fatalities. A way to reduce owl mortality could be to schedule truck traffic outside the hours when owls are most active at hunting around paved roads crossing natural forests, at least during late winter and spring seasons. Because transportation networks encourage future development that will affect the environment in a variety of ways, it is critical to retain roadless and near-roadless (i.e., having only dirt or gravel roads with slow-moving traffic) portions of the southern Andes to preserve their natural landscapes.

Avian electrocutions on overhead power structures are a global conservation concern. Size is an important factor influencing whether a bird perched on an electric utility pole is at risk of electrocution, with larger species and larger individuals at greater risk. Ideally, electric poles should protect the largest species (typically Aquila or Haliaeetus species), but protection measures are expensive, making implementation a challenge when a utility's service area does not include eagles. In these cases, avian protection is sometimes omitted, leaving smaller species at risk because compromise recommendations are unavailable. Flesh-to-flesh distances are a primary determinant of electrocution risk because feathers are only slightly more conductive than air. Metacarpal-to-metacarpal dimensions are particularly important because they quantify the total horizontal distance which can be bridged by the flesh of a bird, but few studies describe metacarpal-to-metacarpal dimensions of at-risk species. Here, we report metacarpal-to-metacarpal and carpal-to-carpal dimensions of 230 raptors of 27 species undergoing rehabilitative care following injury in the wild. Carpal-to-carpal measures facilitate comparison with early efforts by the Avian Power Line Interaction Committee. Our maximum measurements for female Bald Eagles (Haliaeetus leucocephalus), Ferruginous Hawks (Buteo regalis), and Red-tailed Hawks (Buteo jamaicensis) exceeded the range previously reported. Wildlife resource managers and electric utility personnel should use metacarpal-to-metacarpal measurements when considering whether a utility pole poses electrocution risk to a particular species. Future research should include reporting these dimensions for at-risk species world-wide so retrofitting recommendations can be further defined beyond North America.