Date of Award

Spring 5-1-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Andrea Grunst

Second Advisor

Zuyi Gooley

Third Advisor

Rusty Gonser

Abstract

Arctic seabirds are facing increasing stress from climate change, yet the interactive effects of multiple stressors on behavior remain poorly understood. Adopting a multiple stressor perspective promises to advance understanding of avian behavioral responses to climate change, as climate change is exposing Arctic and subarctic animals to a complex set of stressors rather than a single stressor in isolation. Using the red-legged kittiwake (Rissa brevirostris) as a model, I examined how multiple stressors, including mercury (Hg) exposure, shifting wind conditions, and varying foraging conditions linked to sea surface temperature (SST) may interact to constrain behavioral plasticity and energetically expensive behavior (flight, long-distance foraging trips) during the breeding season on St. George Island, Pribilof Islands, Alaska. The Pribilofs are a subarctic archipelago in the southeastern Bering Sea near the continental shelf, where upwelling promotes high marine productivity. The islands host >75% of the global population of red-legged kittiwakes, allowing for an excellent study system to investigate how changes in Hg contamination, wind conditions, and SST combine to influence the behavior and breeding success of this range-restricted seabird. Previous research has shown that red-legged kittiwakes have blood Hg concentrations above proposed toxicological thresholds. High Hg concentrations in combination with energetically expensive flapping flight and a specialized diet consisting primarily of mesopelagic myctophid fish, may make them vulnerable to changing foraging landscapes and wind patterns. I investigated combined impacts of Hg contamination and environmental variables on kittiwake behavioral characteristics using detailed speed and turn GPS data, which allowed me to determine time activity budgets (TABs) based on three behavioral states: transit flight (high speed-low turn), area-restricted search (foraging high speedhigh turn, and resting (both low speed behaviors) and foraging trip characteristics including total trip duration, total trip distance, maximum distance from the colony, and trip direction. I assessed Hg concentrations in blood and feathers, utilizing feathers to evaluate carryover effects from winter stress. I hypothesized 1) climate change-associated challenges, such as higher SST and high winds, may reshape red-legged kittiwake activity budgets, 2) Hg contamination may constrain the capacity of seabirds to adjust to climate change-associated stressors, and 3) overwintering stress may constrain behavioral responses to climate change-associated stressors during breeding. Using GPS data from 27 adults (55 complete trips), I quantified time-activity budgets (TABs) and foraging trip metrics. Wind speed was the only significant positive predictor of trip duration, while SST, wind direction, sex, and Hg were not significant predictors of trip duration, total distance, or maximum distance. TABs showed a significant positive association between SST and time in transit flight (predicted increase of ~11% from a low of 6.79 °C to a high of 7.84 °C SST), while resting showed a weak negative trend and foraging was unchanged. Directional analyses indicated decreasing northness with increasing SST and a significant SST × wind-speed interaction. During my field season, under warmer SST conditions, red-legged kittiwakes tended to travel further south in relation to the colony and the strength of this shift depended on wind speed, demonstrating that birds adjust the direction of their trips in response to both wind conditions and changes in SST. Adult blood Hg averaged 2.11 μg/g and was significantly higher in males than females; head-feather Hg averaged 4.10 μg/g and did not differ by sex. Adult body weight was positively associated with blood Hg. No significant associations were detected between adult and chick Hg; chick blood Hg was negatively associated with chick body mass, suggesting a dilution effect in larger, faster-growing chicks. Spatial analyses showed high overlap between early and late season foraging areas, but late-season locations were farther from the colony. Overall, climate-related variables (SST and wind) explained variation in key behavioral metrics, whereas Hg did not interact with climate stressors to constrain trip behavior or activity budgets. These results suggest that climate variability may be a stronger driver of short-term behavioral shifts than Hg exposure, although Hg remains elevated above proposed toxicological thresholds and shows sex- and offspring-related patterns that could have longer-term fitness consequences. My results showed that climate variables do affect behavior and TABs, whereas Hg did not measurably constrain behavioral flexibility in response to changing environmental conditions. Carryover effects were not evident in behavioral responses, although the association between chick body mass and blood Hg concentrations points to growth-related dilution dynamics that may have fitness consequences. Ultimately, this research provides novel insights into behavioral and ecological constraints on red-legged kittiwake adaptation to climate variability and delineate critical foraging areas of conservation concern in a rapidly changing ecosystem.

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