Penguins Strike Back: A Report on the Unusual Case of Adelie Penguin (Pygoscelis adeliae) Attacks on South Polar Skua Nests Distant from the Breeding Colony

Abstract

In Antarctica, penguins aggressively defend their territory from skuas in order to guard their offspring, since skuas frequently prey on penguins’ eggs or chicks. We present unusual photographs in which south polar skua (Stercorarius maccormicki) nests were attacked by Adelie penguins despite being far from the penguin colony. To the best of our knowledge, this is a previously unreported interesting case in which the Adelie penguin attacked and caused egg loss at skua nests far from the penguins’ colony. The aggressive behaviors of the Adelie penguins to breeding skuas are expected to have occurred elsewhere without penguin colonies, but this has not been reported yet. In this study, such cases were captured on motion capture cameras for the first time. Although penguins broke a skua egg, when we checked the situation before and after the incident in a series of photos, they seemed to take interest in only adult skuas rather than the eggs. Only one skua egg was lost in the three nests, and we confirmed that all of the other eggs and chicks fledged with success. Therefore, the egg loss by Adelie penguins seems to be unintended, and our observation is an interesting case of showing aggression to the predator regardless of the prey’s reproduction. Unusual inter-specific behavior and reciprocal interactions between two Antarctic top predator avian species observed from our survey will be helpful to enrich understanding of interactions among the biodiversity in the Ross Sea region. In addition, we expected that the motion-capture camera can improve observation of Antarctic seabirds without time limit.