Factors affecting adult foraging and chick growth of Adelie penguins (Pygoscelis adeliae) off the western Antarctic Peninsula: A modeling study

FACTORS AFFECTING ADULT FORAGING AND CHICK GROWTH OF ADÉLIE PENGUINS (PYGOSCELIS ADELIAE ) OFF THE WESTERN ANTARCTIC PENINSULA: A MODELING STUDY Erik W. Chapman Old Dominion University, 2009 Director: Dr. Eileen E. Hofmann Coupled individual-based models that simulate Adélie penguin (Pygoscelis adeliae) adult foraging behavior and chick growth from hatching to fledging were developed and used to explore factors that influence adult foraging energetics and chick fledging mass off the western Antarctic Peninsula (WAP). Adélie penguin colonies in this region are undergoing changes in population size that have been correlated with climate-driven alteration of the marine environment. Simulations were selected to highlight possible linkages between these population changes and climate variability, adult foraging, and chick growth processes. Simulations using the chick-growth model 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 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)]. In the chick-growth model simulations, shifting peak Antarctic krill spawning from early December to early March reduced fledging mass by 12%, enough to reduce a 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 mass by 5%. 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. The negative effects of reduced provisioning and wetting on chick growth can be compensated by an increase in AC3 Antarctic silverfish in the chick diet. Results from the coupled models showed 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. Overall, results highlight many opportunities for future observational and modeling studies. They also suggest that a shift in the timing of krill spawning, which is linked with climate-driven processes that determine the availability of phytoplankton biomass, may be having important consequences for Adélie penguins and other toppredator species that time critical activities to coincide with dependable availability of prey with maximum energy density. Also, results suggest that the loss of Antarctic silverfish from the diets of Adélie penguins in some parts of the WAP may have limited the ability of adults to compensate for the negative effects on chick growth of climate-related increases in chick wetting and reduced quality and availability of Antarctic krill.