From trips to bouts to dives: temporal patterns in the diving behaviour of chick-rearing Adelie penguins, East Antarctica

Breeding Adelie penguins forage at sea and return to land to provision their chicks, adjusting their foraging behaviour in response to environmental fluctuations over time. At Becher-vaise Island, a nesting site in an East Antarctic population, Adelie penguin diving behaviour remains undocumented. This represents a key area of uncertainty in efforts to understand and predict foraging success at this colony. We compiled a multi-year telemetry dataset from time-depth recorders deployed from 1992 to 2004 on 64 birds at Bechervaise Island. We examined diving activity at multiple scales, ranging from foraging trips (n = 125) to dive bouts (n = 3461) to individual dives (n = 84 521), and then characterised the stage- and sex-specific variation in diving behaviour of chick-rearing Adelie penguins using linear mixed effect models. Total foraging trip effort (trip duration, number of dives, vertical distance travelled and number of wiggles [a proxy for prey ingestion]) substantially increased as the chick-rearing period progressed (guard through creche), consistent with increasing chick provisioning and self-maintenance requirements over time. Foraging activity was predominantly structured in periods of sustained diving bouts, indicating sustained foraging effort over the course of the foraging trip. Diving behaviour (dive-level depth, duration, bottom time and attempts of catch per unit effort) varied in relation to sex and chick-rearing stage. Dives were performed more frequently during high and low levels of solar light, which is likely linked to visual predation strategies or prey activity. Our findings advance our understanding of this population's foraging behaviour, which is ultimately required to underpin the conservation and management of this breeding colony.