ABSTRACT 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.

ABSTRACT 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.

The identification of breeding habitat is essential for the implementation of conservation efforts for threatened species. Using seven natural and anthropogenic variables, and based on 27 nesting attempts over 17 yr, we created a species distribution model for Harpy Eagle ( Harpia harpyja ) breeding habitat across 5636 km 2 in the Pacific Region of Darien Province, Panama. Highly suitable habitat had high forest cover, low elevation, and a relatively low distance to rivers. We identified specific breeding habitat associations for Harpy Eagles and found that 34% of the area analyzed contained highly suitable breeding habitat. At the regional level, highly suitable habitat was found predominantly in the northern portion of the study area in the four watersheds occurring there, and along the Pacific Coast. The Juradó watershed in the south contained relatively little habitat, owing to a high amount of mountainous terrain. Among three protected areas in the region, Darien National Park contained an equal amount of habitat as the relatively smaller and neighboring Chepigana Forest Reserve and Serranía de Bagre Biological Corridor, a fact that highlights the importance of northern forests for the conservation of Harpy Eagles in Darien. Generally speaking, areas with the greatest amount of human influence were associated with greater forest loss and less suitable habitat. We therefore propose that community-based strategies for sustainable resource management are needed to mitigate forest disturbance levels in areas where the Harpy Eagle coexists with humans. Considering the high importance of the breeding habitat for the Harpy Eagle in the Serranía de Bagre Biological Corridor and Chepigana Forest Reserve, we recommend a revision of the legislation that governs the extractive use of the natural resources in these two protected areas. Resumen Un Modelo Predictivo de Hábitat Revela Especificidad en Harpia harpyja , Una Rapaz Forestal Ampliamente Distribuida La identificación del hábitat reproductivo es esencial para la implementación de esfuerzos de conservación en especies amenazadas. Usando siete variables naturales y antropogénicas y basados en 27 intentos de anidación a lo largo de 17 años, creamos un modelo de distribución de especies para el hábitat de cría de Harpia harpyja a través de 5636 km 2 en la Región del Pacífico de la Provincia de Darién, Panamá. El hábitat más adecuado tuvo una alta cobertura de bosque, una baja altitud y una proximidad relativamente cercana a ríos. Identificamos asociaciones de hábitat reproductivo específicas para H. harpyja y encontramos que el 34% del área analizada incluyó hábitat reproductivo muy adecuado. A escala regional, el hábitat más adecuado fue encontrado predominantemente en las cuatro cuencas presentes en la porción norte del área de estudio y también a lo largo de la costa del Pacífico. La cuenca del Juradó, en el sur, presentó relativamente poco hábitat adecuado, debido a una alta cantidad de terreno montañoso. De las tres áreas protegidas en la región, el Parque Nacional Darién incluyó una cantidad similar de hábitat comparada con las vecinas y relativamente menores Reserva Forestal Chepigana y Corredor Biológico Serranía de Bagre. Esto resalta la importancia de los bosques del norte para la conservación de H. harpyja en Darién. En términos generales, las áreas con mayor cantidad de influencia humana estuvieron asociadas con mayor pérdida de bosque y menos hábitat adecuado. Por ende, proponemos la necesidad de estrategias comunitarias para la gestión sostenible de los recursos y mitigar los niveles de disturbios forestales en áreas donde H. harpyja coexiste con humanos. Considerando la gran importancia del hábitat reproductivo para H. harpyja en el Corredor Biológico Serranía de Bagre y la Reserva Forestal Chepigana, recomendamos una revisión de la legislación que gobierna el uso extractivo de los recursos naturales en estas dos áreas protegidas. [Traducción de los autores editada]

Species considered raptors are subjects of monitoring programs, textbooks, scientific societies, legislation, and multinational agreements. Yet no standard definition for the synonymous terms “raptor” or “bird of prey” exists. Groups, including owls, vultures, corvids, and shrikes are variably considered raptors based on morphological, ecological, and taxonomic criteria, depending on the authors. We review various criteria previously used to define raptors and we present an updated definition that incorporates current understanding of bird phylogeny. For example, hunting live vertebrates has been largely accepted as an ecological trait of raptorial birds, yet not all species considered raptors are raptorial (e.g., Palm-nut Vulture [ Gypohierax angolensis ]), and not all raptorial birds are considered raptors (e.g., skuas [Stercorariidae]). Acute vision, a hooked bill, and sharp talons are the most commonly used morphological characters for delineating raptors; however, using those characters as criteria may cause confusion because they can be vague and exceptions are sometimes made. Old World vultures, for example, are in the family Accipitridae along with hawks and eagles, and thus are usually considered raptors despite their lack of sharp talons. We define raptors as species within orders that evolved from raptorial landbirds (Telluraves) in which most species maintained raptorial lifestyles. Raptors are therefore all species within Accipitriformes, Cathartiformes, Falconiformes, and Strigiformes. Importantly, we believe that seriemas (Cariamiformes) should also be considered raptors. Our definition combines phylogeny with morphology and ecology, and avoids ambiguity associated with owls, vultures, and shrikes. Establishing a common definition of raptors should improve interpretability across studies and lessen ambiguity of research and management recommendations.

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.