Horizontal-vertical movement relationships: Adelie penguins forage continuously throughout provisioning trips

Background Diving marine predators forage in a three-dimensional environment, adjusting their horizontal and vertical movement behaviour in response to environmental conditions and the spatial distribution of prey. Expectations regarding horizontal-vertical movements are derived from optimal foraging theories, however, inconsistent empirical findings across a range of taxa suggests these behavioural assumptions are not universally applicable. Methods Here, we examined how changes in horizontal movement trajectories corresponded with diving behaviour and marine environmental conditions for a ubiquitous Southern Ocean predator, the Adelie penguin. Integrating extensive telemetry-based movement and environmental datasets for chick-rearing Adelie penguins at Bechervaise Island, we tested the relationships between horizontal move persistence (continuous scale indicating low ['resident'] to high ['directed'] movement autocorrelation), vertical dive effort and environmental variables. Results Penguins dived continuously over the course of their foraging trips and lower horizontal move persistence corresponded with less intense foraging activity, likely indicative of resting behaviour. This challenges the traditional interpretation of horizontal-vertical movement relationships based on optimal foraging models, which assumes increased residency within an area translates to increased foraging activity. Movement was also influenced by different environmental conditions during the two stages of chick-rearing: guard and creche. These differences highlight the strong seasonality of foraging habitat for chick-rearing Adelie penguins at Bechervaise Island. Conclusions Our findings advance our understanding of the foraging behaviour for this marine predator and demonstrates the importance of integrating spatial location and behavioural data before inferring habitat use.

Automated summary

The foraging behavior of Adelie penguins is influenced by changes in horizontal movement persistence rather than following traditional optimal foraging models. Environmental conditions during different chick-rearing stages also impact penguins' movement at Bechervaise Island. Therefore, integrating spatial location and behavioral data is crucial for inferring habitat use.