Non-consumptive factors affecting foraging patterns in Antarctic penguins: a review and synthesis

Abstract

Recent research has clearly shown that the fear of predation, i.e. aversion to taking risks, among meso- predators or grazers, and not merely flight from an apex predator to avoid predation, is an important aspect of ecosystem structuring. In only a few, though well-docu- mented cases, however, has this been considered in the marine environment. Herein, we review studies that have quantified behavioral responses of Adelie penguins Pygoscelis adeliae and emperor penguins Aptenodytes forsteri to the direct presence of predators, and question why the penguins avoid entering or exiting the water at night. We also show, through literature review and new analyses of Adelie penguin diving data, that Antarctic penguins are capable of successful prey capture in the dark (defined here as \3.4 lux). Finally, we summarize exten- sive data on seasonal migration relative to darkness and prey availability. On the basis of our findings, we propose that penguins' avoidance of foraging at night is due to fear of predation, and not to an inability to operate effectively in darkness. We further propose that, at polar latitudes where darkness is more a seasonal than a year-round, daily fea- ture, this ''risk aversion'' affects migratory movements in both species, consistent with the ''trade-off'' hypothesis seen in other marine vertebrates weighing foraging success against predation risk in their choice of foraging habitat. Such non-consumptive, behavioral aspects of species interactions have yet to be considered as important in Southern Ocean food webs, but may help to explain enig- matic movement patterns and choice of foraging grounds in these penguin species.