Climate and landscape change are expected to affect species' distributions and interactions, with potentially harmful consequences for specialist predators. Availability of optimal prey can affect reproductive success in raptors, especially in the Arctic, where dramatic differences in prey availability occur both within and between years. However, behavioral responses of dietary specialist, resident predators such as Gyrfalcons (Falco rusticolus) to changes in prey availability remain poorly understood. To improve understanding of how climate-driven changes in prey availability may affect diet of avian predators in the Arctic, we characterized Gyrfalcon diet on the Seward Peninsula, Alaska, in 2014 and 2015 from images representing 2008 prey items obtained by motion-activated cameras at 20 nests. We documented two important dietary shifts: the proportion of ptarmigan (Willow Ptarmigan [Lagopus lagopus] and Rock Ptarmigan [L. muta]) in the diet declined throughout the brood-rearing period in both years, and also differed between years. In both cases, ptarmigan were replaced by Arctic ground squirrels (Urocitellus parryii) in the diet. Despite shifts in prey composition, dietary breadth did not change, which revealed a facultative shift in prey use in which Gyrfalcons relied on prey of large size rather than prey of a particular taxon. We describe previously undocumented prey-use patterns during Gyrfalcon breeding, specifically an interchange between two prey species that are keystones in tundra ecology. These results are important for informing predictive models of climate change and adaptive species management plans. Further study of the interchange between prey types described in this study can strengthen insight into key ecosystem processes, and the cause and effect of potential decoupling of predator-prey interactions.

Burrowing Owls (Athene cunicularia) have a large geographic range spanning both North and South America and resident populations occur on many islands in the eastern Pacific Ocean and the Caribbean Sea. Many owl populations are isolated and disjunct from other populations, but studies on genetic variation within and among populations are limited. We characterized DNA microsatellite variation in populations varying in size and geographic isolation in the Florida (A. c. floridana), the Western (A. c. hypugaea), and the Clarion (A. c. rostrata) subspecies of the Burrowing Owl. We also characterized genetic variation in a geographically isolated population of the western subspecies in central Mexico (near Texcoco Lake). Clarion Burrowing Owls had no intrapopulation variation (i.e., fixation) at 5 out of 11 microsatellite loci, a likely outcome of genetic drift in an isolated and small population. The Florida subspecies had only polymorphic loci but had reduced levels of genetic variation compared with the more-widespread western subspecies that occurs throughout western North America. Despite the extensive geographic distribution of the Western Burrowing Owl, we found genetic differentiation between the panmictic population north of the Trans-Mexican Volcanic Belt and the resident Texcoco Lake population in central Mexico.

The Near Threatened Grey-headed Fish-Eagle (GHFE, Ichthyophaga icthyaetus) has undergone a moderately rapid population decline due to habitat degradation. We studied population density and nest-site characteristics of the GHFE at Noakhali, Bangladesh, between November 2015 and January 2016. We used distance sampling along eight line transects to estimate GHFE breeding density. At each nest, we recorded height and crown density of nesting tree, and distances from nearest human settlement, waterbodies with commercial fisheries (hereafter, commercial waterbodies), and waterbodies without commercial fisheries (hereafter, noncommercial waterbodies). We estimated 0.27 (95% CI: 0.15–0.49) GHFE nests or 0.54 individuals per km². We detected a total of 26 nests, with 85% built on siris (Albizia spp.) trees. All nests were built on the tallest tree within the vicinity of the nesting site, with an average height of 12.5 ± 1.5 m, and on trees with open (69%, n = 18) canopy structure. We found that 76.9% of nests were located within 100 m of human settlements (χ² = 4.13, df = 1, P= 0.04) and 73.1% were located closer to a commercial waterbody than a to noncommercial waterbody (χ² = 13.4, df = 1, P= 0.0002). Total area of commercial waterbodies within 500 m of nests was higher than that of noncommercial waterbodies (W= 507, P= 0.001). These results indicate that GHFEs do not require undisturbed or natural waterbodies and can survive well in some human-modified landscapes if adequate food (e.g., commercial fisheries) and tall trees for nesting are available; thus the species may be less vulnerable to environmental changes than previously thought.

We studied the prevalence of a louse fly (Olfersia fumipennis) in a dense breeding colony of Ospreys (Pandion haliaetus) at San Ignacio Lagoon, Baja California Sur, Mexico. We determined fly prevalence and infestation intensity of 45 nestlings (age 32–59 d). We found louse flies in 65% of the nests sampled (n = 34). Louse fly prevalence in nestlings (n = 45) was 56%, the highest rate reported for any raptor species. Male and female nestlings showed similar levels of fly prevalence and infestation, possibly because the numbers of each sex in this population were similar. We found that louse flies had a spatially dispersed distribution, such that the proximity of any nest to any other within the colony did not influence the prevalence of louse flies nor the louse fly load. The productivity of nests with parasitized young (1.3 ± 0.5 young/nest) was similar to that of nests with young that were not parasitized (1.4 ± 0.6 young/nest; P > 0.05). In terms of spatial location, the overall productivity (number of young per successful nest) of the colony was affected by louse fly prevalence. The condition of coloniality (i.e., high density of nests) likely caused high overall louse fly prevalence. A high prevalence of parasitism might be part of the cost of nesting in colonial conditions. Additional studies on the prevalence of louse flies and the health and body condition of nestlings are needed to evaluate the health of Osprey populations.

Enticed by the migratory irruption of 2007, we established three banding stations in northeastern Alabama, USA, to determine the prevalence of Northern Saw-whet Owls (Aegolius acadicus) in the state and subsequently examine the broader extent of migration patterns and demographics at latitudes ≤35°N. We captured 202 Northern Saw-whet Owls between 2007 and 2016, with annual totals ranging from 3 in 2014 to 64 in 2012. The proportion of hatch-year owls captured was 38.1% overall, which was considerably lower than levels reported at more northern stations. Morphometric estimates and a sex-specific discriminant function analysis table indicated 63.9% of all Northern Saw-whet Owls captured were female and 11.9% were males, with the remaining 24.2% of undetermined sex. Peak migration occurred during mid-November. We locally recaptured 44 individuals and determined that recaptures were bimodally distributed, with most owls recaptured 1 wk after initial banding and a second peak 10–13 wk afterward. We estimated 50% of owls emigrated from stations within 3 wk of initial banding. We encountered seven owls initially banded at northern stations; one of these had flown 1518 km from Whitefish Point Bird Observatory, Michigan to Hollins, Alabama. Of these encounters, three were intra-seasonal and represented owls that had migrated at an average rate of 36.2 km/night. Four owls banded in Alabama were encountered during subsequent seasons in the northern United States. Although limited, these data suggest owls follow the Appalachian Mountains and western Great Lakes migration routes into Alabama. Our findings indicate Northern Saw-whet Owls regularly overwinter in northeastern Alabama, although abundances probably vary annually with migration dispersion cycles. We recommend additional Northern Saw-whet Owl banding stations be established across the southeastern United States to further study this secretive species within the southern periphery of its winter range.

Vultures are crucial components of ecosystems as they perform important ecological and aesthetic functions. They provide sanitation services by feeding on carcasses, which would otherwise decay and possibly become a source of disease affecting the health of other animals. In the last few decades, populations have declined drastically, mainly due to the nonsteroidal anti-inflammatory drug diclofenac used in India, Pakistan, and Nepal. In the current study, we investigated the abundance of vultures inhabiting Pir Lasura National Park in Azad Jammu and Kashmir, Pakistan, from September 2015 to August 2016. We recorded three vulture species, including near-threatened Himalayan Griffons (Gyps himalayensis), endangered Egyptian Vultures (Neophron percnopterus) and critically endangered White-rumped Vultures (Gyps bengalensis), distributed across elevations ranging from 560–1530 masl. The Himalayan Griffons were the most common in the surveyed region (n = 128 individuals), followed by White-rumped Vultures (n = 48 individuals), and Egyptian Vultures (n = 41 individuals). Mean numbers of birds at roosts ranged from 7–20 for Himalayan Griffons, 14–26 for Egyptian Vultures, and 15–23 for White-rumped Vultures. We also identified a previously unknown roost of White-rumped Vultures that could be a potentially important area of conservation focus given the decline of this species in Pakistan. Due to declining populations in other parts of the world, the vulture populations we studied should be regularly monitored as a partial assessment of their conservation needs.

In northern California, USA, western Burrowing Owls (Athene cunicularia) use burrows in active California ground squirrel (Otospermophilus beecheyi) colonies for nesting and protection. Ground squirrels have well-developed, anti-predator alarm-calling behavior, but the potential benefits of such alarm calling to Burrowing Owls have not been examined. The objective of this study was to assess the rate and types of predator interactions experienced by Burrowing Owls and the extent to which they may benefit from alarm calls given by California ground squirrels. We studied interactions of California ground squirrels and Burrowing Owls at Moffett Federal Airfield in urban Santa Clara County, California, during two Burrowing Owl breeding seasons, in 2012 and 2013, using cameras and direct observations. We detected 177 approaches by predators, four of which resulted in predation events on owls. The rate of predator approach during diurnal periods, as determined by direct observation, was 0.93/hr. Ground squirrels called in response to predator approaches before owls did 66% of the time, which was approximately proportional to the abundance of ground squirrels and Burrowing Owls. When squirrels called first, an estimated 75% of owls exhibited alert responses, including alarm calling, running to the burrow, and scanning, indicating that owls benefited from ground squirrel alarm calls in response to approaching predators. Our research suggests that healthy ground squirrel populations may provide important predator alert services to Burrowing Owls, especially in the context of increasing populations of urban predator species.

Apex predators are sensitive to human disturbance and persecution, often becoming the first losses in a declining urban wildlife community. A population of Crowned Eagles (Stephanoaetus coronatus) within eThekwini municipality, KwaZulu-Natal, South Africa, persists in a green space network called the Durban Metropolitan Open Space System (DMOSS). We used GPS–UHF telemetry to investigate the home range and habitat use of five breeding adult Crowned Eagles for 1 yr. We documented a mean annual home range for four birds of 13 km² (Minimum Convex Polygon [MCP] 100%), or 6.3 km² (Kernel Density Estimator [KDE], bandwith H_LSCV 95%), equating to small home ranges for this large eagle, compared with other large eagles. Habitat use within home ranges and correlation with DMOSS area underscored the importance of retaining forest patches in the urban mosaic landscape to encourage the persistence of this large raptor. Our study highlighted the importance of planning green space in future city expansion and land development. The spatial and habitat associations of Crowned Eagles may be used to inform urban planners who wish to support biodiverse communities that include apex predators in an urban landscape.

Peregrine Falcons (Falco peregrinus) on the Canary Islands are considered to be of the Barbary Falcon subspecies (F. p. pelegrinoides). Here we report on lost falconry birds present among the wild population of resident falcons, and provide rough approximations of their abundance for Tenerife, the largest island of the Canaries. We observed lost falconry birds breeding with natural wild falcons, with at least one mixed pair producing fledglings. Only 54.1% of the breeding adults that we studied on the island showed typical Barbary Falcon plumage. Some nest sites were systematically poached, affecting the overall productivity of the population. Our findings suggest that the original Canarian Barbary Falcon population could be suffering from genetic mixing due to the presence of individuals originating from outside the population and from illegal harvest of nestlings. We recommend that local authorities continue to assess the degree of genetic admixture that occurs in this population, modify the current falconry regulations, implement management actions to prevent new escapes, eradicate exotic raptors, and put a stop to illegal nestling harvests.

Hybridization in wild raptors is uncommon, but direct observations of successful hybridization exist. Subsequent introgressive hybridization (i.e., hybrid backcrossing), however, is less commonly reported in the raptor literature. We document (1) an interspecific Ferruginous Hawk (Buteo regalis) breeding attempt, and (2) introgressive hybridization within the genus Buteo. We found photographic evidence of a successful breeding attempt between a Ferruginous Hawk and Red-tailed Hawk (Buteo jamaicensis) in Wayne County, Utah, USA. Subsequent photographic observations in 2011 of adult and juvenile Ferruginous Hawk × Red-tailed Hawk hybrids indicate that this hybrid pair may have bred successfully multiple times. In 2017, we photographed an adult Ferruginous Hawk × Red-tailed Hawk hybrid breeding successfully with a Red-tailed Hawk near the same area where the original hybrid pair was documented. Our observations demonstrate that at least some Buteo hybrids are fertile and capable of reproduction; however, we do not know if the second-generation hybrids are fertile.

We documented two cases of polygyny in Eurasian Kestrels (Falco tinnunculus) and studied the behavior, morphology, age, relatedness, and heterozygosity of bigamous and monogamous individuals. Bigamous males tended to have shorter wing chords compared with monogamous males. The provisioning rate of bigamous males was almost twice that of monogamous males, and at the secondary nests was lower than that at the primary nests. Secondary females were smaller (in wing chord) and younger (<2 yr old) than primary and average monogamous females. The neutral heterozygosity of bigamous adults did not differ from that of monogamous adults. We observed minimal aggression between bigamous females, perhaps due to their relatedness. It is unclear why secondary females engaged in polygyny with less investment from the male; however, accepting the bigamous male allowed immature females the opportunity to mate.

The Austral Peregrine Falcon (Falco peregrinus cassini) is widely distributed in Argentina, although studies on its diet are limited. Here we report information on the diet of this falcon in southern Atlantic Patagonia, Argentina. During November and December in 2009 and 2010, we visited nest sites of Austral Peregrine Falcons to collect prey remains to investigate their diet during the breeding season. We identified 72 avian prey remains from seven eyries in 2009 and three eyries in 2010. We documented seven orders of nonpasserines (11 families representing at least 58 individuals [81% of total prey items]). For the order Passeriformes, seven families were represented by 14 individual birds (19% of total prey items). In all, we identified 52 prey remains (72% of total prey items) to the species level. Another 12 birds were identified only to genus and three only to family or subfamily. Body mass for avian prey identified to species (n = 51) ranged from 10.4 g (Troglodytes aedon) to 842 g (Mareca sibilatrix). Nonpasserines provided 96.2% of the estimated biomass of the prey. Although our sample size is limited, compared with previous reports conducted more than 30 yr ago or in recent years but limited to one pair, our observations for ten nests in 2 yr provide novel and current information on avian prey species of Austral Peregrine Falcons. Our study increased the number of prey species documented for these birds for a geographical region where diet information was almost nonexistent, and provided diet data for both the typical and pallid color morphs of this subspecies.