Penguins in the Coal Mine: Unraveling Sentinel Species Responses to Human-Caused Stressors

Abstract

Thesis (Ph.D.)--University of Washington, 2025Given the urgent need to understand the rapid changes in marine systems, seabirds can serve as effective sentinel species, offering valuable insights into marine conditions and food webs across a range of spatiotemporal scales. I explore the use of seabirds—specifically Magellanic penguins (Spheniscus magellanicus) at the large, but declining breeding colony of Punta Tombo, Argentina—as sentinel species in multiple contexts. First, I examined the effects of extreme heat on Magellanic penguin adults and chicks. Due to climate change, extreme weather events are becoming more frequent and severe, leading to an increase in direct, adverse thermoregulatory impacts on wildlife. I document the magnitude of an unprecedented, single-day, heat-related mortality event of Magellanic penguin adults and chicks. Mortality rates of adults were unevenly distributed across the colony, suggesting that the presence of microclimates or easier beach access were important factors to penguin survival. Next, I examined how intrinsic traits, specifically sex and body size, affect the foraging success of adult Magellanic penguins, before examining how extrinsic factors, like commercial fishing impact their foraging success. Many seabird species are sexually size dimorphic, with males and females often displaying different foraging behaviors. Sex-specific differences in foraging are often attributed to sexual size dimorphism, yet few have quantified the foraging success of males and females and/or of large and small conspecifics. We found males brought back 38% more food than females and males were more efficient foragers than females, bringing back 69% more food per day. Size did not influence foraging success or foraging efficiency suggesting sex-specific foraging behaviors or roles during breeding are driving differences in foraging success and efficiency. Understanding competition between fisheries and seabirds is critical for developing ecosystem-based management strategies that balance fisheries harvest and conservation goals. I assessed the effect of commercial fishing hours on the foraging success and foraging efficiency of chick-provisioning Magellanic penguins. We found that (1) as the average number of fishing hours increased within the penguins' foraging area, adult foraging efficiency decreased, and (2) both adult sex and the timing of fishing effort relative to chick age influenced this effect. When adults were feeding small chicks, an increase in the number of fishing hours within the foraging range was associated with reduced foraging efficiency, especially for males. When adults were raising large chicks, however, foraging metrics had no relationship to fishing hours, likely because adults can leave larger chicks for longer and are thus less spatially and temporally constrained in their foraging efforts. These results indicate fishing may not be affecting the amount of food breeding adults acquire on a foraging trip, but the rate at which they acquire it