Local- and large-scale effects of climate change on Pygoscelis penguin habitat and demography

Climate change around Antarctica is coincident with shifts in the distribution and abundance of Pygoscelid penguins, understanding this link between penguins and climate is the motivation behind this dissertation. I conducted two studies at Palmer Station, located along the rapidly warming West Antarctic Peninsula (WAP). First, I examined foraging behaviors of tagged Adelie and gentoo penguins while an autonomous underwater vehicle simultaneously measured Antarctic krill (penguins' main prey) distributions. We detected krill aggregations within the horizontal and vertical foraging ranges of both species. Adelie and gentoo penguins had spatially and vertically segregated foraging habitats, a strategy that may limit competition for food. This reveals that these recently sympatric penguin species were unlikely competing for food, which agrees with recent studies showing that krill biomass is not in decline. This is a notable finding because past studies hypothesized that WAP penguin population declines are mainly driven by increased competition and decreased krill biomass, related to large-scale changes in sea ice concentration (SIC) and sea surface temperature (SST). Second, I found that interannual variability in Adelie penguin chick fledging mass was related to large-scale climate and local weather; chicks weighed less in cold, wet and windy years, suggesting there could be increased thermoregulatory costs for wet chicks. The mass of a chick before fledging the colony is thought to be an important indicator because heavier chicks are more likely to recruit into the breeding population. This direct impact of climate on chicks illustrates that climate change may affect penguins through pathways that are unrelated to sea-ice influenced food webs.;I also conducted two continent-wide studies to understand spatiotemporal changes in Adelie, gentoo and chinstrap penguin breeding habitats throughout each species entire geographic range using SIC and SST from past satellite observations (1981-2010), and for Adelie penguins, I also used global climate model projections (2011--2100). During the contemporary period, predicted habitat suitability largely agreed with population trends and declining Adelie penguin populations experienced more years with warm sea surface temperature compared to populations that are increasing. An ensemble of global climate models suggests one-third of current Adelie penguin colonies may be in decline by 2060 but refugias may exist in parts of the continent beyond 2099, especially in the Ross and Amundsen Seas. I was not able to determine the mechanism relating austral-summer SST and SIC to penguins. SIC and SST may be an indicator of the quality of terrestrial nesting habitats and chick mass, through the high covariation between oceanic and atmospheric conditions, or related to the availability or quality of food resources. This dissertation demonstrates that local and large-scale studies can provide insights into species habitat use, indicators of penguin population trends and ultimately, a greater understanding of the consequences of climate change in the Southern Ocean.