Foraging flexibility in response to at-sea constraints in a deep diver, the king penguin: an experimental study

When foraging, marine top predators rely on increasingly unpredictable oceanographic structures. Central place foragers are particularly affected. Their efficiency at replenishing their body reserves at sea while feeding their offspring on land relies on accurately targeting predictable foraging locations. Therefore, increased time and effort spent searching for resources is likely to compromise reproduction. Here, we used an experimental design to assess the flexibility of breeding king penguin (Aptenodytes patagonicus) foraging behavior in response to harsh conditions at sea, and examined the consequences on the growth and survival of their chick. We tested for behavioral adjustments to compensate for experimentally increased foraging workload, obtained by the application of a hydrodynamic drag effect. Compared to controls, treated adults more directly targeted a predictable hydrographic feature, the Polar Front, while limiting the increased costs of deep diving. Treated adults significantly increased hunting activity at shallower depths where the effect of treatment on diving efficiency was neglectable. Our experiment resulted in decreased body mass gain during the brooding stage of chicks raised by treated parents compare to controls, with no direct effects on chick survival up to the winter period, but significant negative effects during winter. We identified two different strategies for foraging in king penguins: 1) foraging at the Polar Front where prey patches are more predictable and accessible at shallower depths or 2) foraging closer to the colony by targeting preys at deeper depths. These results highlight the possibility of a trade-off between distance and depth in breeding king penguin foraging behavior.