Does foraging success predict subsequent foraging behavior in Pygoscelis penguins?

Abstract

In a patchy prey environment, optimal foraging theory predicts that central place foragers will discretize horizontal movement and vertical movements into directed and resident foraging behaviors and that high foraging success should lead to similar sequential foraging trips. Here we use high resolution GPS and depth records to track the foraging locations and estimate forage success of two Pygoscelis penguin species in a known biological hotspot to test the predictions of optimal foraging theory. Over two breeding seasons, we tagged 71 penguins near Palmer Station in the West Antarctic Peninsula. We estimated foraging activity from the complexity of depth records and linked them to horizontal patterns of resident and directed movements measured by GPS tags. Contrary to theoretical expectations, we found that there was no relationship between movement modes and foraging rate. We also found that the degree of similarity between sequential trips was not predicted by foraging success, wind speed, or tidal stage. Sequential foraging trips were also not significantly more similar to each other than other non-sequential foraging trips. Our overall findings suggest that the penguins in this region forage during both directed and residential movements, which is not expected if they were following optimal foraging theory. The horizontal patterns of resident and directed movements were not good predictors of foraging activity. We suggest that the abundance and reliability of prey in the local region may explain why these penguin colonies do not follow the expectations of optimal foraging theory.