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.

We investigated Golden Eagle ( Aquila chrysaetos ) diet on the Seward Peninsula, Alaska, at 35 and 30 occupied eagle nest sites in July 2014 and 2015, respectively. We used 52 prey remains and 456 regurgitated pellets collected from nest and perch sites to identify 727 individual prey items representing 18 prey categories. Golden Eagles in our study area primarily consumed Arctic ground squirrels ( Urocitellus parryii ; 52% of total biomass), ptarmigan ( Lagopus spp.; 20%), and waterfowl (15%). Dietary breadth differed between years. We detected 13% more ptarmigan and 12% fewer ground squirrels at perch sites compared to nest sites. Our results suggest that Golden Eagles have a relatively broad dietary niche in western Alaska during the first half of the breeding season.

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.

The Short-eared Owl ( Asio flammeus ) is a widespread raptor whose abundance and distribution fluctuates in response to the varying amplitudes of its prey, which are predominately microtines. Previous efforts to describe the seasonal movements of Short-eared Owls have been hindered by few band recoveries and the species' cryptic and irruptive behavior. We attached satellite transmitters to adult Short-eared Owls at breeding areas in western and interior Alaska in June 2009 and July 2010, and tracked their movements for up to 19 mo. Owls initiated long-distance southward movements from Alaska and most followed a corridor east of the Rocky Mountains into the Prairie provinces and Great Plains states. Four owls followed a coastal route west of the Rocky Mountains, including one owl that crossed the Gulf of Alaska. Completed autumn migration distances ranged from 3205–6886 km (mean = 4722 ± 1156 km [SD]). Wintering areas spanned 21° of latitude from central Montana to southern Texas, and 24° of longitude from central California to western Kansas. Subsequent seasonal migrations were generally northward in spring and southward in autumn; these movements were comparatively short-distance (mean = 767.5 ± 517.4 km [SD]) and the owls exhibited low site fidelity. The Short-eared Owls we tracked from two relatively local breeding areas in Alaska used a patchwork of diverse open habitats across a large area of North America, which highlights that effective conservation of this species requires a collaborative, continental-scale focus.