Golden Eagles (Aquila chrysaetos) can prey on a wide variety of species, but population persistence is often thought to depend on the abundance of a few key prey species. We investigated Golden Eagle prey remains at 254 nesting sites in north-central Utah, USA, from 1970–2014. We hypothesized that variation in observed prey at the nesting site could be predicted by ecoregion or localized (6.4-km radius) environmental factors. We identified 147 prey species representing a minimum of 26,734 individuals, with the majority of species occurring at low frequencies. Golden Eagle prey remains were dominated by black-tailed jackrabbits (Lepus californicus), with cottontails (Sylvilagus spp.), rock squirrels (Otospermophilus variegatus), and yellow-bellied marmots (Marmota flaviventris) also found frequently, and occasionally in large numbers per nesting site. We found natural groupings of prey species by multivariate analyses. Nonmetric multidimensional scaling (NMDS) identified three prey assemblages typical of sagebrush (Artemisia spp.)steppe, wetland, and mountain ecosystems. Canonical correspondence analysis (CCA) and permutational multiple analysis of variance (PERMANOVA) suggested that prey assemblages were associated with environmental variables, including: (1) forest cover and elevation vs. sagebrush and pinyon pine (Pinus spp.) cover; and (2) alfalfa (Medicago sativa), crop, and wetland cover vs. elevation and forest, sagebrush, and pinyon pine cover. Observed prey were better predicted by measured environmental factors than biogeographic boundaries. The abundance of the four most frequently recorded prey species was influenced primarily by habitat, and to a lesser degree by overall diversity of prey remains, precipitation, and time trend variables, as suggested by Poisson regression models. Our analyses indicate that Golden Eagle prey varied within and between ecoregion boundaries, and that prey were more strongly predicted by localized environmental factors than by climate or time.

Habitat suitability for breeding birds is defined at scales ranging from the landscape to individual nesting sites. Nesting site characteristics that govern exposure to inclement weather may affect breeding success, although attempts to understand this effect for Arctic breeding raptors have yielded ambiguous results. Further, breeding adults incur substantial costs from incubating eggs and brooding nestlings, and it is possible that greater site exposure results in increased nest attendance rates, increasing their cost of breeding. We quantified nesting site characteristics of Gyrfalcons (Falco rusticolus) and assessed how breeding parameters and nest attendance rates varied by protective site qualities on Alaska's Seward Peninsula, 2014–2019. The degree of physical exposure in the horizontal plane correlated negatively with the probability of hatching and fledging (provided hatch occurred), as well as overall productivity. The negative effect of horizontal exposure on the probability of fledging and productivity was greatest at nesting sites that were also more exposed in the vertical plane, although this interaction did not affect the probability of hatching. Early breeding pairs had higher productivity and tended to select more protected nesting sites. Additionally, nest attendance rates were higher in more horizontally exposed nesting sites, particularly when nestlings were approximately 2 wk old. The increased nest attendance and concurrent decreased productivity associated with greater nesting site exposure demonstrated that nesting site characteristics can have direct and indirect effects on Arctic breeding raptors and also highlight the importance of small-scale variables when evaluating habitat suitability.

Conservation of predators requires a comprehensive understanding of their life history and ecology, including the delineation of temporal and spatial dietary habits. Gyrfalcons (Falco rusticolus), Willow Ptarmigan (Lagopus lagopus), and Rock Ptarmigan (L. muta) are Arctic specialists, strongly linked in a dynamic predator-prey relationship, and facing similar conservation threats. We studied Gyrfalcon predation of ptarmigan on Alaska's Seward Peninsula and investigated whether species-specific contributions to diet reflected preferential selection or exploitation of the more abundant prey species. Additionally, we examined how the sex ratios of ptarmigan in Gyrfalcon diet varied throughout the breeding season. We collected ptarmigan prey remains from in and around occupied Gyrfalcon nesting sites in 2017, and identified species and sex by molecular techniques. We compared proportions of the two ptarmigan species in Gyrfalcon diet to proportions of the Rock and Willow Ptarmigans' preferred habitat around Gyrfalcon nesting sites (n = 205 skeletal remains from 12 nests), and compared sex ratios of ptarmigan prey remains temporally (n = 252 skeletal remains from 12 nests). We found that prey remains were more likely to be Rock Ptarmigan when areas around Gyrfalcon sites had greater slope and higher elevation (i.e., they better matched the habitat preferences of Rock Ptarmigan), which may suggest Gyrfalcon diet tracked ptarmigan availability without preference for species. Ptarmigan remains were biased toward male birds during June, when most female ptarmigan are incubating on concealed nests. Although we recommend additional analysis of these topics, our findings further our understanding of Gyrfalcon and ptarmigan ecology as the Arctic faces rapid changes to its climate and landscape.

Owls can be difficult to detect due to their secretive behavior, typically low calling rate, and low density on the landscape. Low detection probability during surveys can result in an underestimation of the presence and abundance of a species. Thus, optimizing detection probability of surveys targeting owls is necessary to accurately address ecological questions. We used datasets collected in South Carolina, USA, and Alberta, Canada, to investigate how survey detection can be optimized for Barred Owls (Strix varia). We examined seasonal effects on the detection probability of Barred Owls as determined by playback surveys and autonomous recording unit (ARU) surveys, and whether daily patterns of Barred Owl vocal activity could be used to improve the efficiency of ARU surveys. For each survey method, we estimated the number of survey days needed to obtain a seasonal detection probability ≥ 90% of Barred Owls. We found detection probability with playbacks increased as the breeding season progressed. The effect of seasonality on detection probability with ARUs was dependent on the way encounter history was defined. Barred Owl vocal activity peaked twice per night, with one vocalization peak occurring immediately after sunset and another 7–9 hr after sunset. By targeting these vocalization peaks during surveys, we found that we could reduce ARU survey time by 50% and still retain .82% of the original site detections, thereby reducing survey processing time. Although playback surveys were more efficient than ARU surveys at detecting Barred Owls, ARUs have numerous advantages, such as reducing survey effort and disturbance to the target animal. Ultimately, survey designs are dictated by the budget, personnel capacity, study region, and research objectives, but our findings will help researchers plan studies that optimize detection probability and minimize survey cost and effort.

Audio playback of vocalizations by conspecifics is commonly used to elicit calls when surveying birds of prey. Methods for call surveys vary widely in their use of silent listening periods, and usually range from 3–15 min in length. We aimed to refine this approach for detecting Great Horned Owls (Bubo virginianus) in Arctic Alaska, which is the northernmost limit of their breeding range. We used two playback protocols: protocol 1 entailed uninterrupted playback, whereas protocol 2 interspersed silent listening periods with playback during 12-min surveys. In playback surveys consisting of 166 point counts during the 2017 and 2018 breeding seasons, the probability of detecting a Great Horned Owl was 0.46 (95% CI ¼ 60.09) with protocol 1 and 0.35 (95% CI ¼ 60.12) with protocol 2 (P ¼ 0.18). The probability of detection rose with the length of the playback: of all owls detected during the 12-min surveys, 23% (95% CI ¼ 66.4%) responded within the first 3 min, 52 6 7.6% within the first 6 min, and 80 6 6.1% within 9 min. Including silent listening periods was not necessary for detecting Great Horned Owls during call surveys. We found no correlation between probability of detection and either cloud cover or wind speed (P ¼ 0.60 and P ¼ 0.28, respectively). However, we found a negative correlation between temperature and probability of detection (P ¼ 0.02). From these surveys, we calculated the density of Great Horned Owls in the Middle Fork Koyukuk Valley, Alaska (approximately 67.589°N, 149.789°W) was 4.2 6 2.6 owls/km² during the winters of 2017 and 2018, which represents the first estimate of density at the northern breeding limit of the species.

Bald Eagle (Haliaeetus leucocephalus) populations throughout North America have increased considerably since the ban of DDT in 1972 and eagles now inhabit suburban areas in large numbers. To better understand the ecology of urban populations living in south-coastal British Columbia, we compared nest-site characteristics, reproductive rates, and diets of more than 150 breeding pairs of rural-, suburban- and urban-nesting eagles in the Greater Vancouver area. Three-quarters of the nests were located within 230 m of buildings and roads, or within 31 m of a potential source of disturbance. Urban eagles nested in live, taller trees that were close to the edges of patches, whereas rural eagles used shorter trees and occasionally human-made structures such as transmission towers. Eagles at nests located close to patch edges and in areas with greater human land use had higher reproductive rates than those at isolated nests or in remote rural habitat. Waterfowl and gulls (family Laridae) were common in the diet across the study area, but urban eagles also used alternative sources such as C-O sole (Pleuronichthys coenosus), Bufflehead (Bucephala albeola), and Band-tailed Pigeon (Patagioenas fasciata). Eagles in the Vancouver area have adapted to human-altered landscapes; management strategies should focus on maintaining edge habitat, monitoring population expansion in urban areas, and protecting nest sites.

Several lines of evidence support the hypothesis that abiotic and biotic factors directly or indirectly control species' distributions. Despite the importance of assessing the environmental factors governing species' distributions, it is not clear how such factors influence migratory species. We evaluated environmental factors related to the nonbreeding distribution (September through March) for Harlan's Red-tailed Hawks (Buteo jamaicensis harlani), using a maximum entropy (Maxent) approach. We evaluated records spanning the nonbreeding season from 1 September to 31 March, gathered from four different sources including online data and published literature; we used maximum and minimum temperatures, precipitation, solar radiation, wind speed, and cloud cover as abiotic factors. Based on the most influential environmental factors (determined using percent contribution, a measure representing the increase in likelihood associated with each environmental factor), we delineated the current winter distribution (December through February) and evaluated niche overlap. From December through February, we found that minimum temperature showed the highest percent contribution (62.2%, 55.9%, and 66.9% in each month, respectively). Response curves for minimum temperature were quadratic in shape in September, non-monotonic in shape in October, and sigmoid in shape in November, December, January, and February, with high suitability values for temperature ranging from 0–20°C and low suitability for temperature,0°C. However, habitat suitability decreased at higher levels of solar radiation (.6000 kJ m^–2 d^–1) during fall migration (September, October) and spring migration (March). Our revised winter distribution map, based on ecological niche modeling, includes areas of ecoregions not previously included in Harlan's Hawk range maps in the western USA, and northeastern Mexico.

The Cooper's Hawk (Accipiter cooperii) is often classified as a woodland species, but it exhibits marked plasticity by nesting successfully in what was previously thought to be atypical habitat such as urban areas and sparsely wooded grasslands, including the Little Missouri National Grassland in North Dakota. Forest expansion into North Dakota grasslands is likely due to the reduction of natural disturbances such as wildfires and grazing by bison (Bison bison). From the 1970s to 2001, forest cover increased in McKenzie County, North Dakota, by .1000%. From 1950 to 1972 there were two recorded instances of nesting Cooper's Hawks in McKenzie County. In 2001, we recorded 18 active nests, 13 of which were successful, four that failed, and one with unknown fate. Using the 2001 National Landcover Dataset (NLCD), we calculated that the mean proportion of forest cover in circular plots (18.1 km²) surrounding nests was 0.21. We found no relationship between nest fate and proportion of forest land cover. Additionally, we found no significant difference in proportion of forest cover between nest sites and randomly selected sites centered on forest land cover, indicating that Cooper's Hawks were using forest land cover in proportion to its availability. Understanding the relationship between the shifting landscape composition of North Dakota and its avifauna is important for monitoring and managing breeding Cooper's Hawks.

The Egyptian Vulture (Neophron percnopterus; Accipitridae) is a medium-sized scavenger distributed throughout most of the Indo-Pak subcontinent. Although the species has been listed as endangered on the IUCN Red List since 2007 due to rapid population decline, scientific data about the species' population trends and ecology in Pakistan are sparse. The present study was conducted in and around Poonch River Mahasheer National Park (PRMNP) in the northeastern part of Pakistan, covering an area of approximately 146 km². To monitor populations, we used the line transect method to survey 11 sites once per year from May 2013 to May 2019. Based on monitoring data at all 11 sites, the total number of vultures observed averaged 84 birds annually (n ¼ 7 yr, range ¼ 64–131), with the greatest number observed in 2019. Congregation sites of the vultures were closer to settlements (mean ¼ 239 m) and rivers (mean ¼ 1119 m) than to dump sites (mean ¼ 2975 m), though some roost sites were very near (,200 m) dump sites and roads. Roost sites included large pine (Pinus roxburghii) trees, electric pylons, rocks, and cliffs. To better understand population status and dynamics, we recommend studies extending across a larger area and including surveys of the nesting population.