Weather is thought to influence raptor reproduction through effects on prey availability, condition of adults, and survival of nests and young; however, there are few long-term studies of the effects of weather on raptor reproduction. We investigated the effects of weather on Northern Goshawk (Accipiter gentilis; henceforth goshawk) breeding rate, productivity, and fledging date in south-central Idaho and northern Utah, USA. Using data from 42 territories where we found evidence of breeding attempts in ≥1 yr from 2011–2019, we analyzed breeding rates using 315 territory–season combinations, analyzed productivity for 134 breeding attempts, and analyzed fledging date for 118 breeding attempts. We examined 35 predictor variables from four categories: precipitation, temperature, wind, and snowpack. Of the variables we evaluated, April precipitation, previous year's April–July precipitation, April–May mean temperature, and March–May mean temperature were related to measures of goshawk reproduction. Greater April–July precipitation in the previous year and lower April precipitation in the current year were associated with higher breeding rates. Years with warmer average April–May temperatures were associated with increased goshawk productivity. Years with greater April–July precipitation during the previous year and lower mean March–May temperatures were associated with later fledging dates. Based on these relationships, we considered projected changes in weather in the northern Great Basin over the next 50 yr as a result of climate change (without directly accounting for habitat changes caused by climate change), and predicted that climate change will: (a) have no significant effect on goshawk breeding rate, (b) have a positive effect on goshawk productivity, and (c) cause a shift toward earlier goshawk breeding. Our results indicate that weather is significantly related to goshawk reproduction in the northern Great Basin, and we suggest that the relationship between raptor breeding and weather be further investigated to enable higher resolution predictions of how changes in the climate may influence their populations, particularly changes that may not have been captured by our study.

Ospreys (Pandion haliaetus) are adaptable fish-eating raptors that readily nest on artificial structures in heavily human-dominated areas. Although the Osprey is a well-studied species, few researchers have investigated the factors that influence nest success and productivity in an urban environment. We monitored Osprey nests from 2013 to 2017 in highly urbanized Pinellas County, located on the west coast of central Florida, USA. We used logistic exposure models to assess the effects of timing of nesting, nest attributes (nest substrate, height), and landscape-level variables (inter-nest distance, distance to water, and surrounding habitat type) on daily survival rate (DSR) of Osprey nests. The number of active nests (i.e., nests with eggs) in the study area ranged from 53 in 2013 to 79 in 2016, with an overall total of 329 during the 5-yr study. Although most nests produced at least one young near fledging age, 131 of the nests failed. We attributed 45% of nest failures to storm events and 50% to unknown causes. The best logistic exposure model specification included only two variables: the discrete variable representing the date incubation started and the nominal variable indicating the year 2015. Osprey nests initiated earlier in the season were more likely to survive, and later nests (initiated after 22 April) averaged only one fledgling each. Osprey nests in 2015 had the highest DSR and relatively few failed due to storms. Our results supported previous research indicating that early nesters were more successful than late nesters. Our results also indicate that storms may play a role in nest success of Ospreys in Florida. Other variables, such as the amount of urbanized land surrounding Osprey nests did not appear to influence nest survival, indicating that Ospreys can be productive even in highly urban environments.

Estimating species density and abundance is challenging but important for establishing conservation and management strategies. Significant progress has been made toward estimating Golden Eagle (Aquila chrysaetos) abundance in the conterminous United States of America (USA) but much less is known about eagle abundance in Alaska. Here, we paired migration count and GPS-tracking data collected near Gunsight Mountain, Alaska, in a Bayesian framework to estimate the number of Golden Eagles in south-central Alaska. We estimated 1204 (95% credible interval: 866, 1526) potentially breeding (≥4 yr old) Golden Eagles annually moved through the Gunsight Mountain migration corridor and summered over an area of 150,325 km² in south-central Alaska, equating to a density of 0.80 potentially breeding eagles/100 km². By extrapolating across the species' nesting range in Alaska (1,180,489 km²) and incorporating published productivity and age-specific survival rates for eagles <4 yr old into our hierarchical model, we estimated 12,717 (95% credible interval: 9043, 16,349) Golden Eagles of all ages occur in Alaska, annually. We propose this as a conservative statewide population estimate because we used methods that likely underestimated population size. Even so, our estimate is three to five times larger than previous estimates and likely represents about one quarter of the USA's population.

Raptors face threats such as habitat modification, climate change, and environmental pollutants in many parts of the western USA, where rapid human population growth exacerbates such pressures. However, information about distribution of raptor nests at broad spatial scales that could inform conservation efforts is lacking. To provide a contemporary estimate of nest distribution of four raptor species of special conservation concern (Bald Eagle [Haliaeetus leucocephalus], Ferruginous Hawk [Buteo regalis], Golden Eagle [Aquila chrysaetos], and Prairie Falcon [Falco mexicanus]) throughout Colorado, we used a statewide database of raptor nesting locations to inform species distribution models for monitoring and management efforts. We used generalized linear models to identify the relationship between nest locations and explanatory covariates relating to land cover, temperature, topography, and prey distribution. We investigated the effect of different methods for selecting the sample of locations available to raptors, comparing four selection frames: sampling from the observed locations of the target-group (i.e., other raptor nests), sampling from within a spatial buffer around observed locations, sampling from outside of the same buffer, or complete random sampling of the background locations without respect to observations. Out-of-sample validation techniques indicated strong predictive accuracy of our models. Each raptor species was best represented by a different one of the four approaches to sample available locations, refuting our expectation that models accounting for bias would perform better than those that did not. Our findings were consistent with generally understood habitat associations of these species. These models can be used to identify hot spots with high relative probability of use by breeding raptors and to inform future monitoring practices that use a standardized, stratified sampling design.

Plumage pigmentation is fundamental to a bird's phenotype, with pigment deposition causing relative crypsis or conspicuousness, depending on the environmental context. Geographic variation in plumage melanin tends to be predictable, suggesting that aspects of climate cause local matching of plumage to environment via genetic adaptation. Ecogeographic rules describe this predictability: Gloger's rule predicts that populations in wetter and warmer environments will be more pigmented; Bogert's Rule predicts more pigmentation in cold environments. The Great Horned Owl (Bubo virginianus) exhibits extensive geographic variation in the degree of melanin-based pigmentation. We examined fine-scale spatial variation in owl plumage melanism along environmental gradients in southwestern North America. We tested whether variation is explained by either of two non-mutually exclusive hypotheses: (1) a history of allopatric divergence between subspecies or (2) in situ local adaptation consistent with ecogeographic rules. The allopatric divergence hypothesis predicts a bimodal distribution of plumage melanism, with a geographic cline across a zone of secondary contact, whereas the local adaptation hypothesis predicts that climate explains variation independently of geography. Using a colorimeter, we measured coloration in 101 museum specimens of breeding-season Great Horned Owls that had been obtained from variable environments and elevations. Specimens previously identified as separate subspecies were distinguishable by colorimetry. Plumage lightness, however, was continuously distributed, rather than bimodal. While accounting for males having reduced pigmentation relative to females, linear models revealed that lighter plumage was associated with low latitude, low elevation, high temperature, and low precipitation. These findings suggest that variation in Great Horned Owl plumage pigmentation is best understood as continuous ecogeographic variation, consistent with ecogeographic predictions, and currently maintained in situ along multiple environmental gradients that characterize the “sky island” topography of the southwestern USA.

The endangered Tasmanian Wedge-tailed Eagle (Aquila audax fleayi) is the focus of continued research and conservation efforts. A tool for accurate and efficient identification of the sex of individuals would be a valuable aid to research and management. However, plumages are monomorphic between the sexes, making sex identification difficult without molecular analyses. Our aim was to assess whether Tasmanian Wedge-tailed Eagles of different age classes could be sexed accurately using morphological measurements. We took measurements of 25 live late-stage eagle nestlings and 108 carcasses of free-flying birds found opportunistically throughout Tasmania. Sex of all individuals was confirmed via genetic analyses. Free-flying birds were larger than nestlings; thus, we used age-specific statistical tools to distinguish the sexes. For both nestlings and free-flying birds, females were significantly larger than males, but overlap between the sexes prevented accurate sex identification using any single measurement. We used stepwise linear discriminant function analyses to select morphometric measurements necessary for accurate sex identification. Free-flying birds could be sexed with 97.6% accuracy using a combination of measurements of the forearm length, tarsus width (i.e., lateromedial width), and hallux length. Late-stage nestlings (9–10 wk old) could be sexed with 95.4% accuracy using measurements of the hallux width (i.e., lateromedial width), hallux breadth (i.e., anteroposterior width of hallux), and tarsus breadth (i.e., anteroposterior width of the tarsometatarsus at the narrowest point). The discriminate functions we present also allow the identification of sex in cases where morphological sex identification may be in doubt and molecular analyses should be prioritized. These equations provide a valuable research tool for studies of sexual differences in behavior and causes of mortality of this endangered subspecies.

Accurate estimations of adult mortality are essential for understanding population dynamics and achieving efficient management actions that are directed toward long-lived species. Several noninvasive methods may be used to monitor endangered long-lived birds like raptors, but their performance in real-world scenarios remains poorly studied. We used eight Bonelli's Eagle (Aquila fasciata) breeding pairs (1) to compare the efficiency of direct observations with binoculars and telescopes (2004–2016), camera trapping (2012–2016), and feather genetic analysis (2004–2015) for detecting and identifying individuals over time, (2) to conduct a cost-benefit analysis of methods, and (3) to evaluate the accuracy of the direct observation method for estimating survival by comparing it with camera trapping and feather analysis. Both the feather genetic analysis and camera trapping approaches allowed us to successfully identify individuals and to detect replacements that we did not notice during direct observations. The classic direct observation method overestimated adult survival, which could hamper an accurate understanding of the demographic dynamics of this population. Feather analysis gave a low detection rate of individuals (47%), probably due to difficulties in finding feathers in the rugged habitat of this species. However, identification success at the individual level with this method was 96%. Remote camera surveys had both a high detection rate (100%) and identification success (93%). Given that costs associated with camera surveys were lower than the costs of genetic procedures, we concluded that camera trapping is the most efficient indirect method to assess adult survival in this and other raptors with external features that make individual identification possible. However, because no method showed complete efficiency, genotyping of feathers collected at the end of the breeding season could be a useful additional method, especially when camera trapping is not possible or when it fails.

Studying species that nest underground, such as the Burrowing Owl (Athene cunicularia) is challenging. Ecological and behavioral information about Burrowing Owls is often limited to activities occurring aboveground or to insights gained from live viewing using downhole cameras and burrow scopes with limited recording capacity. Although automated monitoring systems may enhance underground observations, such systems need to be self-powered to support research conducted in remote areas. We describe a self-powered (off-grid) digital video recording system developed in 2014 to monitor nesting Burrowing Owls at Rio Bosque Wetlands Park in El Paso, Texas, USA. We used solar panels, infrared cameras, and digital video recorders to create a self-contained system for monitoring two artificial Burrowing Owl nest sites. From 2014 to 2018, we collected high-resolution video recordings of Burrowing Owl nesting ecology and behavior in their underground artificial burrows and nest boxes in remote areas. We provide detailed instructions and recommendations for the design, construction, installation, and maintenance of this system. Although our system required some initial material and labor costs, it required less on-site work than traditional behavioral observations, while also providing high-quality video images of an understudied aspect of Burrowing Owl ecology. Key ecological insight gained included nest initiation dates, clutch sizes, incubation dates, hatching sequences, prey items delivered to the nest, and predators of Burrowing Owls in the El Paso area. We encountered substantial technical problems but recommend the overall design of our system.

The American Kestrel (Falco sparverius) is in general decline across its North American distribution. In contrast to widespread patterns of decline, kestrel populations appear stable in the southern Great Plains region. Historically, this region had a very low occurrence of kestrels, and their current abundance is highly likely due to vegetation and structures associated with settlement by people of European descent. To determine prey use by breeding kestrels, we placed motion-activated video cameras at preexisting kestrel nest boxes located in the Southern High Plains in 2017. We recorded over 4200 prey deliveries during 1748 hr of observation at five nests over the 4-wk brood-rearing period. On basis of frequency, these deliveries were dominated by reptiles (74.8%), with invertebrates (18.2%), mammals (4.4%), birds (2.9%), and unidentified (1.2%) prey used to lesser extents. Prey delivery rates were high relative to other studies; across the brood-rearing period we recorded an average of 2.3 deliveries/hr, equating to an average of 0.49 deliveries and 3.85 g of prey/nestling/hr. Because invertebrates dominate the diet reported in most kestrel food habit studies, the volume of reptiles captured as prey was unexpected. Even more unanticipated was the number of large prey captured, including juvenile eastern cottontails (Sylvilagus floridanus) and ground squirrels (Ictidomys tridecemlineatus, Xerospermophilus spilosoma). We suspect the proportion of vertebrate prey captured during the nesting season may explain the local high rates of nesting success and number of young fledged.

The effects of weather on an individual can often alter the population dynamics of a species. Knowledge of how weather influences individual behavior is therefore essential in understanding its full impact in the context of population ecology. Snowy Owls (Bubo scandiacus) exhibit expensive long-distance migrations in winters following population irruptions. During irruptive movements, many owls migrate past the southernmost extent of their traditional wintering grounds, the mechanism for which is still debated. We propose and test the “milder climate” hypothesis; Snowy Owls wintering in lower latitudes are better able to meet their metabolic demands due to higher temperatures and lower snow cover. During the Snowy Owl irruption of 2014–2015, we examined this hypothesis by assessing the influence of local weather variables on foraging success, frequency of prey capture attempts, and overall activity budgets in a sample of wintering Snowy Owls in New York, USA. We used eBird, an online citizen science resource, to help locate Snowy Owls, which we observed from an automobile. We found that none of the weather variables tested affected foraging success. However, the lack of effect of snow depth on foraging success may suggest that hearing is more important for hunting in Snowy Owls than previously thought. Hunting frequency decreased with increasing temperatures, suggesting Snowy Owls were better able to meet their metabolic demands in higher temperatures. We thus offer support for the milder climate hypothesis; Snowy Owls wintering in lower latitudes may be able to offset the energetic expenses of long-distance movements.

We estimated occupancy and population abundance of the Andaman Serpent-Eagle (Spilornis elgini) and Crested Serpent-Eagle (Spilornis cheela) in the Andaman Islands, India. We divided the islands that were . 100 km² into a grid of 84 cells, of which we used 34 cells (5 km 3 5 km each) for surveys of two populations in the districts of (1) the North and Middle Andaman Islands, and (2) the South Andaman Islands, which includes Little Andaman Island. We performed single-season, single-species occupancy modeling independently for both regions and single-season, two-species occupancy modeling for co-occupancy in the surveyed landscapes. The estimated abundance for the Andaman Serpent-Eagle and the Crested Serpent-Eagle was 4–5 and 7–8 individuals per 25 km², respectively. The Andaman Serpent-Eagle is commonly distributed in both regions and has a high detection probability (detection probability, P ¼ 0.8). The Crested Serpent-Eagle is widely distributed in the South Andaman Islands with a low detection probability (P ¼ 0.5). The single-season, two-species occupancy model showed that the endemic Andaman Serpent-Eagle occupied only 22% of the area and did not co-occur with the Crested Serpent-Eagle. It also indicates the possible avoidance or exclusion of the Crested Serpent-Eagle by the Andaman Serpent-Eagle. We encountered both serpent-eagles in all the identified habitat types. The Crested Serpent-Eagle's habitat use was not restricted to the coastal forests, as previously reported, and the Crested Serpent-Eagle is probably dominating the Andaman Serpent-Eagle in the co-occupied areas. We further conclude that the occupancy dynamics and competition for space between these two Spilornis species might significantly affect the distribution and population of the vulnerable and endemic Andaman Serpent-Eagle in the future.

Most raptor populations are declining and nearly a fifth are threatened with extinction; thus there is a need to increase collaboration to ensure efficient and effective research, management, and conservation. Here, we introduce the Global Raptor Impact Network (GRIN; www.globalraptors.org), a tool to enhance collaboration and conservation impact of the raptor research community. We provide an overview of the history and current state of GRIN, including plans for expansion. Predecessors to GRIN include The African Raptor DataBank, which was launched in 2012 to ascertain the conservation status of raptors across Africa; and the Global Raptor Information Network, which was launched in the late 1990s as a website to provide information regarding diurnal raptors and facilitate communication among researchers. GRIN expands the data collection and storage capabilities of the African Raptor DataBank to a global scale via mobile application. We have implemented data-sharing rules to ensure the safety of sensitive species, and users of the GRIN mobile app can designate their records as confidential. GRIN staff and partners are developing analyses of species' population trends and geographic distributions to aid in conservation assessments. GRIN is also developing systematic reviews, detailed bibliographies, and online accounts that will summarize the state of knowledge for each raptor species. We hope that GRIN will benefit the entire raptor research community and aid in the collaboration necessary to help raptor populations thrive in the Anthropocene.

Investigating space use of wild birds provides important knowledge of bird behavior and ecology, which is crucial in the management and conservation of threatened species. In the present study, we used GPS satellite telemetry to investigate space use and movements of seven adult Eurasian Eagle-Owls (Bubo bubo) in Norway during breeding and post-breeding seasons. Breeding adults had a mean home range size of 42.9 km² (SD ± 35.1 km²; 95% kernel density estimation H_{ad hoc}), and five individuals performed long (>20 km) excursive movements away from their breeding territories during autumn. Such wide-ranging behavior has not previously been reported for adults of the nominate subspecies B. b. bubo. The study demonstrates the need to investigate seasonal movements of species, populations, and age groups even if they are considered residents, and provides valuable information for management and conservation of the Eurasian Eagle-Owl.

Anthropogenic lead intoxication is the most frequent cause of death of White-tailed Sea-Eagles (Haliaeetus albicilla) in Germany. Most lead fragments are ingested by eagles feeding on carcasses and viscera of game animals shot with lead-based ammunition left in the wild by hunters. We investigated how many regurgitated pellets contained metal fragments and hypothesized a correlation between the presence of metal fragments and (1) the hunting season, (2) the ban of lead in rifle ammunition, and (3) the frequency of specific prey animals in the pellets. We collected 273 regurgitated pellets, radiographed them for metal fragments, and analyzed the prey composition. The metal elements were identified using micro x-ray fluorescence. Metal particles were found in 9.2% of pellets; 24 fragments consisted of lead and one fragment was mostly copper. A higher proportion (14.3%) of contaminated pellets was detected during the hunting season from September through February. During the non-hunting season from March through August, 7.6% of the regurgitated pellets were contaminated. Furthermore, there was a significant positive correlation between the presence of mammalian remains in the pellets and metal contamination (general linear model, z=2.16, P=0.03). Our results indicate a correlation between the increased activity of hunters in winter and the occurrence of metal in regurgitated pellets of White-tailed Sea-Eagles.

The Osprey (Pandion haliaetus) experienced severe declines in Europe over the past centuries, including extirpations from large parts of its range. After Ospreys began naturally recolonizing Wales, United Kingdom (UK), in 2004, the Dyfi Osprey Project initiated an extensive ecological (ringing, satellite tracking, and nest video recordings) and genetic (microsatellite genotyping) monitoring program alongside artificial nest platform construction. From 2004 to 2019 there were 40 reproductive events (i.e., eggs laid in a nest) across six nests, resulting in a total of 95 fledglings and a yearly average of 2.35 ± 0.8 (SD) fledglings per nest-with-eggs. Video recording at one nest documented high hatching success and survival to the fledging and dispersal phases, as well as mate- and nest-fidelity across multiple years. Collectively these breeding parameters suggest high productivity associated with artificial nest structures and limited density-dependent effects for the Welsh population due to its small size and low density at this stage of recovery. Satellite tracking of four migrating individuals revealed that Ospreys used a western European migratory flyway and wintered in sub-Saharan western Africa. Genetic analysis of nestlings from five nests indicated single paternity in all cases, in agreement with evidence of social monogamy. Genetic analysis of geographical outgroups (Scottish, Swedish, and Latvian) provided preliminary evidence of cryptic population structure among UK (Welsh and Scottish) populations. The novel combination of loci show Welsh Osprey retain high levels of variation and more broadly direct reconsideration of the hitherto inferred genetic poverty of the species compared to other raptors. We recommend implementation of similar long-term ecological and genetic monitoring programs for other populations.

A secretive and cautious raptor, the Black Eagle (Ictinaetus malaiensis) is challenging to study. Its highly specialized foraging behavior makes it difficult to capture an individual for tracking. However, a tailless eagle provided an opportunity to describe the home range and movements of one bird for 3 yr from 2013 to 2016. A total of 43 independent photo records were provided by a bird photographers' community. The eagle regularly moved between summering and wintering habitats north and south of Taipei City, Taiwan; home range sizes were estimated as 54.1 and 47.1 km², respectively. This noninvasive case study provides the first estimates of home range size and movement patterns for the Black Eagle, and highlights the contribution of community science to research on endangered raptors.