Weather can affect raptors occupancy (Beardsell et al. 2016), productivity (Mearns and Newton 1988, Anctil et al. 2014), phenology (Heath et al. 2012), prey availability (Robinson et al. 2017), and population size (Selonen et al. 2021). Accelerated Arctic climate change has resulted in significant warming (with seasonal variation), more extreme heat events, increased precipitation (including more frequent and severe storm events), and levels of change are approaching irreversibility (Trenberth et al. 2003, McCrystall et al. 2021, Constable et al. 2022). Among Arctic raptors, species-specific responses are likely, with important implications for the assemblage structure and function (Eeva et al. 2002, Terraube et al. 2017). For example, warmer temperatures may disproportionally benefit habitat generalists, such as Peregrine Falcons, Golden Eagles, or Common Ravens (Peck et al. 2018), giving them a competitive edge over specialists and altering the composition of the assemblage.

Here I propose delineating how contemporary weather patterns affect raptor demographics (Figure 1A) and use existing Gyrfalcon data to validate potential mechanisms including nestling daily survival and prey delivery rate (Figure 1B). Additionally, I will characterize changes in the frequency and severity of weather patterns these analyses reveal as important for raptor demography and forecast future weather changes based on existing climate models. In culmination, my findings should provide a relatively comprehensive assessment of the effects of weather on Arctic raptors and delineate mechanisms that facilitated these effects. Further, identifying future changes will help identify future conservation issues among the Arctic raptor assemblage as they continue to face accelerated change.  

 

1A. Delineating the effects of contemporary weather patterns on the Arctic raptor assemblage on the Seward Peninsula, Alaska.

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There are clear effects of weather on raptors but it remains unclear how species-specific responses are likely to affect assemblage composition and understanding these effects has recently been identified as a research priority (Martínez-Ruiz et al. 2023).  Here I aim to conduct a robust assessment of a variety of parameters to assess potential mechanisms for direct and indirect effects of weather on Arctic raptors, highlight differences among species, and identify specific time windows that have the greatest effects. In this section, I will focus on how weather affects occupancy, productivity, phenology, and prey availability for the Artic raptor assemblage. I will use nest occupancy to estimate the breeding population each year within our study area, correcting for imperfect detection (MacKenzie et al. 2003). Productivity is a critical parameter for population maintenance (Johnson and Geupel 1996) and phenology can affect raptor productivity (Callery et al. 2022), including Gyrfalcons on the Seward Peninsula (Henderson et al. 2021). Lastly, prey availability can decrease from inclement weather applying indirect effects on raptor productivity (Robinson et al. 2017) because prey availability is critical for raptor breeding success (Newton 1979). Ptarmigan are an important prey species for the Arctic raptor assemblage (Johnson et al. 2022), particularly for Gyrfalcons (Barichello and Mossop 2011), and seasonal weather patterns can influence ptarmigan abundance (Kobayashi and Nakamura 2013). Finally, I will delineate weather patterns within discrete annual stages because vulnerability of raptors to inclement weather varies seasonally (e.g., high vulnerability during early-nestling stage [Henderson et al. 2021]). In analyses, I will include various measures of weather because averages and totals can be an incomplete assessment of the impact of weather. For example, the frequency and severity of storm events likely has a greater effect on breeding success than average precipitation during the same period (Anctil et al. 2014).

            I will estimate occupancy, productivity, and phenology from multispecies, biannual surveys conducted from an R-44 helicopter (2005 – present, 550 sites, five species). We conduct occupancy surveys the second week of May to coincide with the incubation period of Gyrfalcons, Golden Eagles, and Common Ravens and the courtship/nest-building periods of Rough-legged Hawks and Peregrine Falcons. I will correct occupancy estimates for detection probability (Booms et al. 2010). We conduct productivity surveys the third week of June to count nestlings and estimate age based on feather development. Due to variable phenologies, I also aim to assess the relationship between nesting age at the time of surveys and the estimated probability of fledging for each species. I will establish this relationship by leveraging nests with known productivity (from nest camera data) to estimate how fledging probability increases with nestling age (80 % fledging ages [Steenhof et al. 2017]). To estimate ptarmigan abundance, we conduct 15, 16-km driving transects biannually. Extreme weather can disrupt ecosystem functions by affecting predators and prey (Schmidt et al. 2019) and in this section I hope to identify the most important effects for the raptor assemblage to better contextualize impacts of altered weather patterns as a result of climate change.  

 

1B. Delineating potential mechanism for the effects of weather on demography by focusing on the Arctic specialist Gyrfalcon.

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Here I delve deeper into the effects of inclement weather on Gyrfalcon nestling survival and prey delivery rate. I will focus on Gyrfalcons because specialists are more at risk to climate change (Hof et al. 2012) and existing data on nestling mortality and prey delivery rates allow me to validate important mechanisms of weather effects. Although nestling survival is an integral component of productivity (quantified in section 1B), delineating daily survival rates will allow me to identify storm characteristics that directly result in nestling deaths (e.g., storm severity and duration). Similarly, although I am assessing the effects of weather on prey abundance in section 1B, prey delivery rates can be more important than abundance (Ontiveros et al. 2005) and examining prey delivery rates can reveal whether inclement weather cause prey to take shelter and reduce their availability. Lastly, I will incorporate a covariate for protective nesting site characteristics that affect productivity (Henderson et al. 2021) because shielding nestlings from inclement weather can reduce metabolic costs (D'Alba et al. 2011).

To quantify daily nestling survival I will record nestling mortalities by viewing nest camera images taken every half hour (n = 70 nests, 2014 – 2022). Similarly, I will leverage detailed diet data from nest cameras (2014 – 2022). I have downloaded all weather data from Nome airport weather station (most complete data for Seward Peninsula), summarized the data by annual cycle stage, and visualized trends for various measures of temperature, precipitation, and wind speed (1900 – 2022). In general, temperatures appear to increase in all annual stages besides courtship. Trends were variable for precipiation with differences among measurement types and annual stages. For example, Figure 2 demonstrates recent changes in above average rain days (average is relative to each stage) and conveys clear differences between various annual stages. Average wind speeds appear to be declining, but it is possible that gusting wind speeds have increased, particularly during the brood-rearing period, which can affect breeding success (Hilde et al. 2016). This research should highlight mechanisms that facilitate effects of weather on raptor demography, which is important for developing any mitigation actions.