We document concentrations of total mercury (THg) in feathers of Peregrine Falcons (Falco peregrinus; hereafter peregrines) collected during autumn migration at South Padre Island, Texas, and Assateague Island, Maryland, from 2009–2015. We detected THg in all sampled fourth primary (p4; range=0.44–37.46 µg/g) and axillary feathers (range=0.09–62.68 µg/g). We found no significant difference in THg concentrations between hatch-year (HY) peregrines by study site. Mean THg concentrations were greater in both feather types of after-hatch-year peregrines than of HY peregrines, but concentrations in p4 feathers of second-year peregrines (mean = 14.9 µg/g) were significantly greater than those of after-second-year individuals (mean = 8.5 µg/g). Pooling samples from HY birds across both sites and all years, we found no significant differences between the concentrations in the axillaries of females (mean = 2.4 µg/g) vs. males (mean = 2.2 µg/g), nor between the two feather types. The concentration associated with toxic effects in peregrines is unknown; however, peregrines have recently experienced broad population expansion across the presumed breeding area of the birds we sampled, and the THg concentrations we measured were lower than those in an apparently healthy breeding population in the southwestern USA. We documented widespread THg exposure in peregrines migrating from the northern latitudes of North America, but additional research is needed to assess trends of mercury exposure in the face of increasing global anthropogenic release of mercury into the environment and the release of long-term sequestered mercury in melting permafrost because of climate change.

Scientific study of raptors often requires the use of a lure to capture individuals for marking or collecting various data and samples. Live lure owls in the genus Bubo are commonly used with mist nets or dho-gazas to trap nesting raptors, but the use of these live lures presents ethical, logistical, and financial challenges. Although owls mounted by taxidermists and mechanical owls have been used in place of a live bird, the success of these types of lures varies widely. We created a more realistic mechanical owl with a greater range of motion than previous models, and then tested the owl on six raptor species in a variety of habitats. For all but one species, capture rates using our mechanical owl were similar to or slightly higher than those reported in studies using live lure owls or previously designed mechanical owls. Time to capture of Northern Goshawks (Accipiter gentilis) was, on average, 8 min faster when using our mechanical owl compared to a live owl. Cost analysis revealed that both the initial expense and long-term maintenance of a mechanical owl were less than that of a live lure owl. Mechanical owls can be a useful tool for capturing raptors. Although there are some drawbacks to using a mechanical owl, our results suggest that mechanical birds are comparable to live lure owls and we believe the benefits of using a mechanical owl often outweigh the costs.

Studies of cliff-nesting raptors can be challenging because direct observations of nest contents are difficult. Our goals were to develop a protocol for installing motion-activated trail cameras at Golden Eagle (Aquila chrysaetos) nests to record diet information and productivity, and to estimate prey detection probability using different diet study methods. In 2014 and 2015, we installed cameras at 12 Golden Eagle nests with 18–42-d-old nestlings. Following installation, we monitored adult behavior using direct observation and post-installation image review. At two nests, adult eagles did not return to nests or exhibited behaviors suggesting avoidance of the cameras, but returned to the nests after cameras were removed. We visited the 10 remaining nests every 4 d to collect prey remains and pellets to generate prey-specific detection estimates for both images, and prey remains and pellets. Compared to inspection of prey remains and pellets, cameras recorded twice the number of prey (622 vs. 316), were more likely to detect the smallest and largest prey, and cost half as much. Cameras recorded productivity, fledging dates, and in one case, a nestling death. Trail cameras may be a reliable and cost-effective option to address clearly defined research goals and obtain required information about eagle behavior and nest contents. However, cameras should be used judiciously because installation creates a persistent manipulation at the nest. Camera appearance should be minimized, and post-installation monitoring that allows for timely responses to nest-avoidance behavior by adult eagles is important to prevent adverse effects on nesting success.

Golden Eagles are a long-lived, wide-ranging bird of conservation concern in North America. To create a comprehensive conservation strategy, managers and researchers need to know the primary causes of mortality and must have reliable survival estimates. We monitored nesting Golden Eagles in a 2700 km² area of south-central Montana from 2010–2017. As part of our effort, we fitted 16 adult and 13 nestlings with platform terminal transmitters for satellite telemetry. We determined causes of mortality from recovered Golden Eagles and, using multi-state models in program MARK, we estimated monthly and annual survival probabilities. We confirmed five total mortalities, including two cases of lead toxicity, one occurrence of intraspecific aggression, and two mortalities with unknown cause. The monthly survival estimate of adult Golden Eagles in our study area was 0.994 and the annual adult survival probability was 0.930. The monthly survival probability estimate from birds transmittered as nestlings was 0.991 and the annual survival estimate was 0.897. Lead toxicity and intraspecific aggression are known causes of Golden Eagle mortality, but the birds we tracked died from lead toxicity at a higher rate than would be expected based on results from other studies. The survival probability estimates from the Golden Eagles we monitored were higher than reported estimates from other locations. Further, the information we provide can assist with the development of population matrices and increase our knowledge on causes of Golden Eagle mortality.

The Taita Falcon (Falco fasciinucha) is a globally vulnerable cliff-nesting, bird-eating raptor, sparsely distributed down the eastern side of sub-Saharan Africa. It seems to occur in small, isolated pockets of a few breeding pairs, clustered around localized patches of ideal habitat. One such pocket has been the Batoka Gorge system on the Zambezi River, immediately downstream of Victoria Falls on the border of Zimbabwe and Zambia. The species was first recorded here in the late 1950s, and subsequent observations over the next 40–50 yr established Batoka Gorge as an important location for this species worldwide. Regular and intensive surveys in the early to mid-1990s identified at least six breeding territories in the first 40 km of the gorge, and a strong likelihood of more pairs farther downstream. We surveyed this same section of the gorge in July 2013 and November 2014, accumulating >100 hr of observation time at previously occupied Taita Falcon sites. This was the first systematic search of the area for Taita Falcons in nearly two decades. Although we found similar numbers of cliff-nesting Peregrine Falcons (F. peregrinus) and Verreaux's Eagles (Aquila verreauxii) as in the earlier surveys, we did not record any Taita Falcons in the area. The reasons for this decline in numbers and the implications of this finding for the conservation status of this little-known species remain speculative.

We investigated the flight altitude of hunting Eleonora's Falcons (Falco eleonorae) around their colony near the island of Crete (Greece). We used a broadband marine surveillance radar positioned on the coast of Crete and detected the falcons’ movements during the breeding period. The birds were monitored using a Java application that enabled us to manually track radar targets directly on the radar screen and transfer the data into a GIS environment. Thirty hours of radar monitoring between 14 September and 22 September 2017 produced 4774 records of the species (1218 over inland and 3556 over the sea). Hunting falcons flew on average at 1292 ± 11 masl (range = 17–3475, median flight altitude 1156 m), though 70% of them were tracked flying between 17 and 1750 m. The range of flight altitude recorded was greater than that previously published, and was consistent with the prey selection during the nestling-rearing period, i.e., migratory passerines. Eleonora's Falcons hunted more frequently over the sea than over the mainland and at a higher altitudes during the morning than at midday or in the afternoon. The daily flight pattern probably reflected the higher intensity of passerine migration in the early morning and late afternoon, as well as an opportunistic prey shift from birds to insects during midday when passerine migration is weak. Compared to other techniques previously used for tracking this species, namely visual observations (1970s), optical range finder (1990s), and satellite telemetry (2000s), broadband marine radar is not limited by small sample size, geolocation error, weather conditions, or poor visibility at high altitudes.

We studied Northern Hawk Owls in Montana from 1994 through 2015. We report 36 breeding records, 18 of which included a known nest location. Owls reused one nest in subsequent years, but this nest was included only once in our analysis of nest-site characteristics. All nests were in moderate to severely burned forests from 1–11 yr post-burn. Nests were found in black cottonwood (Populus trichocarpa; n = 6), quaking aspen (P. tremuloides; n = 6), Engelmann's spruce (Picea engelmannii; n = 3), and western larch (Larix occidentalis; n = 2). Average nest tree height was 19.6 ± 3.4 m (95% CI, n = 17), average nest height was 14.1 ± 1.6 m (95% CI, n = 17), and average diameter at breast height was 43 ± 4 cm (95% CI, n = 17). Average measurements of nest tree height and nest height were larger than those reported from elsewhere in North America. Diet, based on 274 prey identified from pellets, was 88% voles, most frequently Microtus pennsylvanicus (51%, n = 140). Only 1 of 72 banded owls was recaptured or recovered over the course of this 22-yr study, suggesting a non-sedentary or nomadic population with low site fidelity. The lone recapture represents the first report of a philopatric Northern Hawk Owl in North America. Although this owl is still considered a rare breeder in the conterminous United States, we documented breeding records in 11 of the last 12 yr of this study. All but four known breeding records in Montana occurred within Glacier National Park.

We studied the diet and prey delivery behavior of Burrowing Owls (Athene cunicularia hypugaea) during the breeding season in the southeastern Chihuahuan desert, Mexico. The diet of the Burrowing Owl included 8 orders, 13 invertebrate families, and 5 genera of mammals, gastropods, reptiles, and birds. By frequency, invertebrates (Orthoptera, Coleoptera, Hymenoptera, and Hemiptera) were the most common prey, with vertebrates making up a much smaller proportion. However, by biomass, owls consumed mainly vertebrates (56.7%). Among invertebrates, the families Tenebrionidae and Acrididae accounted for 33.2% of the total consumed biomass. Females delivered more prey items than males (55.6% and 44.4%, respectively). Our observations contribute to our knowledge of the ecology of this owl in a region where it has been little studied.

We studied migration of a female and male Red-tailed Hawk (Buteo jamaicensis) from southern California with satellite telemetry over 9.3 and 6.7 yr, respectively. Previous research suggested the migratory fraction of southern California's Red-tailed Hawk population was limited to juveniles and young adults, and that these hawks ceased migrating once they acquired a territory and mate, usually at 3 yr of age. Both hawks in this study ceased migrating at 3 yr of age, the year they both first nested, and did not migrate for the next 4 and 3 yr, respectively. However, both hawks resumed migrating in 2014, the year with the lowest recorded precipitation in California history. The male did not migrate in 2015, the last year we were able to track his movements, while the female switched between migrating (2015 and 2017) and residency (2016) over the next 3 yr. To our knowledge, our study is the first to document individual raptors displaying such switching behavior.

We examined Golden Eagle (Aquila chrysaetos) brood survival in relation to spring temperatures and exposure of nests to afternoon sun in southwestern Idaho from 1970 through 2012. Most (77%) nests classified as shaded in a subset of 96 nests had northwest to east aspects, and most (71%) nests classified as exposed had south to west aspects. We analyzed survival of 1154 Golden Eagle broods in 64 territories. Golden Eagle brood survival at shaded and exposed nests did not differ when the daily maximum temperature was <32.2°C. Survival in exposed nests declined as the number of days with maximum temperature ≥32.2°C increased, but survival in shaded nests did not change. All broods survived from hatching to fledging age in eight exposed nests with artificial shade structures installed over a 6-yr period. During the same period, 7 of 42 broods in nests without shade structures failed to reach fledging age, with two failures (29%) attributed to thermal stress. Use of artificial shade structures in exposed nests may reduce or prevent mortality caused by heat stress, and thus might be a potential tool for mitigation of “take” from anthropogenic structures and activities. Additional experimentation under an adaptive management framework could provide more information about the effectiveness of using shade structures to offset nestling mortality associated with increasing temperatures predicted by climate change models.

The Snowy Owl (Bubo scandiacus) is a rare resident species in Iceland and nests have been found intermittently. Nests are unusual because lemmings (Dicrostonyx spp. and Lemmus spp.), the primary prey of the Snowy Owl across much of its distribution, do not occur in Iceland. We studied summer diets by analyzing pellets from three areas in Iceland where owls were detected; breeding was confirmed at two of these sites. We identified 257 prey items (total mass of 73.6 kg) of at least 13 species. Birds made up most of the diet (96.5% by number). The Rock Ptarmigan (Lagopus muta) was the primary prey species (30.4%). Shorebirds were important prey (46.2%), and passerines (5.1%), as well as waterfowl (6.3%), were also taken. Wood mice (Apodemus sylvaticus; 2.7%) and Arctic fox pups (Vulpes lagopus; 0.8%) were taken occasionally. Adult prey birds made up 60.3% and nestlings 36.3% of the diet by number.

The Steppe Buzzard (Buteo buteo vulpinus), an eastern subspecies of the Common Buzzard (Buteo buteo), is a long-distance migrant raptor that breeds across eastern European and central Asian grasslands. The eastern European populations migrate through a geographic bottleneck in Israel and overwinter in eastern and southern Africa. To investigate how the metabolic demand of long-distance migration may affect their health, we trapped Steppe Buzzards (n = 28) at Eilat, Israel, during the spring migration of 2016 and 2017 and collected their parasitic lice (Insecta: Phthiraptera). We compared their louse infestation levels to published data on nonmigratory or short-distance migratory Common Buzzards (B. b. buteo). These Common Buzzards were divided into two groups, free-living birds (n = 59) and captive ones (n = 104). All the Steppe Buzzards we examined harbored 1–4 species of lice. The Amblyceran lice that feed partially on living tissues and are thought to be relatively more virulent (Laemobothrion maximum and Colpocephalum nanum) were significantly more prevalent on Steppe Buzzards than on Common Buzzards (either free-living or in captivity). In contrast, the less-harmful Ischnoceran lice (Craspedorrhynchus platystomus and Degeeriella fulva) were either similarly or less prevalent on Steppe Buzzards than on the nonmigratory Common Buzzards, either free-living or in captivity. We hypothesize that this difference may mirror the metabolic demands of long-distance migration or, alternatively, our Eilat sample of Steppe Buzzards might have been biased in favor of the heavily infested individuals. In the Steppe Buzzard sample, we also detected a formerly unknown negative correlation between the abundance of Laemobothrion maximum and Colpocephalum nanum.