Effects of krill demography on the foraging behavior and habitat use patterns of Adelie (Pygoscelis adeliae) and Gentoo (Pygoscelis papua) penguins breeding at Palmer Station, Antarctica

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Along the Western Antarctic Peninsula (WAP), populations of Pygoscelid penguins are undergoing significant demographic shifts, coincident with rapid environmental warming. Ice-obligate Adelie penguins have experienced significant population declines around Palmer Station, where ice-intolerant Gentoo penguins have recently established themselves and have since grown in number near the southernmost extent of their range. These demographic shifts have been attributed to sea-ice loss, and in more northern areas along the WAP downward Adelie population trends have been attributed to declining krill stocks. The objective of this study is to investigate the influence of krill recruitment variability on the foraging behavior and reproductive success of Adelie and Gentoo penguins at Palmer Station. Previous research has found that diet samples of Adelie penguins indicate cyclical patterns of krill recruitment, with strong cohorts emerging every 4-6 years following bursts of phytoplankton productivity. The mean foraging trip duration of Adelie penguins has been found to increase during breeding seasons following poor krill recruitment. This study will use a combination of diet data and concurrent satellite and dive telemetry to investigate the effects of variable krill recruitment on the diving behavior and the foraging ranges of Adelie and Gentoo penguins across six breeding seasons (2010-2015). During the chick-rearing phase of each breeding season, roughly 20 adult birds were instrumented with satellite transmitters and time depth recording tags to document the location and record the dive profiles of daily foraging trips. Tags were recovered after roughly three days. Independent diet samples were obtained during the same time period and will be analyzed to determine penguin diet and krill size-frequency distributions. We predict that poor krill recruitment will result in increased foraging effort by both species, characterized by more frequent and longer foraging trips, and an increase in dive rate and dive frequency. We hypothesize that 1) Adelie penguins will be limited by diet and dive behavior and will experience reduced chick-rearing success in breeding seasons following poor krill recruitment while 2) Gentoo penguins will alter their diets and dive behavior to maintain chick-rearing success in years following poor recruitment. In addition to this, we hypothesize that in years following reduced krill recruitment, the extent of habitat-use overlap between these two species will be greater. Ultimately, this study will provide us with a better understanding of the behavioral responses of Adelie and Gentoo penguins to environmental variability, and it will leave us better informed to infer population-level responses to reduced prey and increased competition in the Palmer region.