A novel foraging strategy in gentoo penguins breeding at sub-Antarctic Marion Island

To help meet the high energy demands of raising the young, some seabirds alternate between short, frequent foraging trips to maximize food delivery to the young, and infrequent, long foraging trips that serve towards self-maintenance. Our study is the first to investigate the foraging behaviour of gentoo penguins at Marion Island, which we did through a combined use of GPS loggers and time-depth recorders. The shallow shelf between Marion and Prince Edward Islands proved to be an important foraging area, and penguins exploited this area using a novel foraging strategy. Penguins undertook alternating trips of relatively short and long durations. Short trips, performed in the afternoon, were likely associated with self-maintenance as they were followed by roosting on the beach overnight and not returning to the colony. They were followed by longer and more distant foraging trips, after which birds returned to the colony to provision chicks. To our knowledge, this is the first study to demonstrate alternating trip lengths in gentoo penguins and the first to associate short trips with self-maintenance in seabirds. We suggest that due to the close proximity of a predictable foraging area for these penguins at Marion Island, there is minimal energetic cost to return to land after self-provisioning. Hence, unlike other seabirds that feed at greater distances from their breeding colonies, gentoo penguins are afforded the opportunity for short self-maintenance trips. Finally, we argue that these birds may be using this novel strategy due to sub-optimal feeding conditions resulting from environmental change.