Gemma Carroll, Martin Cox, Robert Harcourt, Benjamin J. Pitcher, David Slip and Ian Jonsen
In many natural systems, prey is distributed patchily across the landscape. Dense groups of individual prey items are clustered within patches of lower prey density, that are in turn separated by areas where prey is scarce. This is the case in the open ocean, where marine predators are faced with the challenge of finding prey that is both patchy and constantly on the move. We looked at spatial patterns of prey capture by the smallest penguin species – the little penguin – in south eastern Australia. While we tracked the penguins with GPS and acceleration devices that could identify prey capture, we also surveyed their feeding area from a small boat with an acoustic ‘fish finder’ to independently examine the distribution of their prey. We found that overall, there was a “match” between where penguins foraged and where there were shallow schools of prey. This was related to features of the marine environment that might help penguins find prey, such as water temperature and salinity. We found that the distances between two consecutive prey capture events by a penguin occurred on two scales: a short scale (less than 10 m) that corresponded to the size of prey schools, and a larger scale (more than 50 m) that corresponded to movements between prey patches. This gives insight into how predators move around and find prey when it is distributed in patches. Finally, we found that there were features of individual schools that helped penguins catch prey, with penguins catching more prey in areas where schools were dense, compact and shallow. Our study shows that foraging by predators is finely tuned to the patchiness of their prey at different spatial scales, and helps us to understand the strategies that animals have evolved to find food in complex environments.
Image caption: Penguin capturing prey.
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