Adelie penguin (Pygoscelis adeliae) colonies in off the western Antarctic Peninsula (WAP) are undergoing changes in population size that have been correlated with climate-driven alteration of the marine and terrestrial environment. Climate-associated changes in the environment may affect chick growth processes which are important because large chicks are more likely to recruit to the breeding population and Adelie penguin population dynamics can correlate with fledging mass. In this study, coupled individual-based models that simulate Adélie penguin chick growth and adult foraging behavior during the chick growth period were developed and used to explore factors associated with climate variability that influence chick fledging mass and adult foraging energetics off the WAP.

Chick growth model simulations tested the influence on penguin chick fledging mass of variability in 1) timing of Antarctic krill (Euphausia superba) spawning, 2) chick diet composition [Antarctic silverfish (Pleuragramma antarcticum) combined with Antarctic krill compared to an all-Antarctic krill diet], 3) provisioning rate; and 4) the extent to which chicks become wet (from rain or melting snow). Simulations coupling the adult-foraging and chick growth models investigated the influence on adult mass, foraging energetics, and chick growth of variability in 1) prey-availability characteristics (prey ingestion rate and distance between colony and prey), 2) the extent to which adults prioritize self-maintenance over chick provisioning, 3) adult digestion rate while foraging (a poorly studied physiological rate), and 4) adult diet composition [Antarctic krill combined with Antarctic silverfish (50% female) compared to all-Antarctic krill (50% and 100% female)].

Shifting the peak Antarctic krill spawning from early January to mid-February, an environmental stress that results in more than a 4% reduction in provisioning rate, or wetting of just 10% of the chick's surface area decreased fledging mass enough to reduce the chick's probability of recruitment. Introducing a minimal amount of third-year age class (AC3) Antarctic silverfish to an Antarctic krill diet increased Adélie penguin fledging sufficiently to increase recruitment. The negative effects of reduced provisioning and wetting on chick growth can be compensated for by an increase in AC3 Antarctic silverfish in the chick diet. The foraging model simulations found that increasing adult ingestion rate, decreasing distance to prey, increasing adult digestion rate, feeding only on female Antarctic krill, and including Antarctic silverfish in the diet increased the range in prey-availability characteristics over which adults can raise full-sized chicks.

Results suggest that future studies should be directed at improving our knowledge of the energetic and physiological constraints on adult Adelie penguin foraging and chick growth. Overall, results suggest that the loss of Antarctic silverfish from the diets of Adelie penguins in some parts of the WAP may have limited the ability of adults to compensate for the negative effects of climate-related changes in the marine (reduced Antarctic krill abundance) and terrestrial (increased wetting of chicks) environment.