17 July 2011

Fear-based feeding: why penguins don’t eat in the dark

Who's afraid of the dark?
Adelie penguin at Palmer Station,
Antarctica. Photo credit: Johnny Shaw.
Some rights reserved.
ANTARCTICA - Monsters under the bed may seem an irrational reason for human children to be afraid of the dark, but for penguins the monsters of the night are very real. Research published recently in the journal Polar Biology shows that penguins make choices about where and when to feed based on their fear of being eaten by the predators lurking in the dark.

The review and new analysis by researchers David Ainley of HT Harvey and Associates and Grant Ballard of PRBO Conservation Science looks at Adélie and emperor penguin feeding behaviour in the context of risk aversion or “fear of being eaten”, as opposed to simply “going where the food goes”.

The researchers found that although the penguins can find food successfully in dark conditions, such as those found deep under the Antarctic sea ice, the birds do not enter or leave the water in the dark of night. Entering and leaving the water is a time when penguins are susceptible to being eaten by leopard seals or killer whales, and doing so in the dark, when the penguins can’t assess whether or not predators are present, appears to hold more risk than penguins are willing to take.

“This could explain why we have observed both emperor and Adélie penguins making seemingly unnecessarily long trips during migration, passing by areas with large food concentrations and selecting places that have at least a couple of hours of daylight every day, even in winter,” said David Ainley.

The authors point to the recent, mysterious disappearance of an emperor penguin colony as potential corroborating evidence that predators can have severe impacts on penguin populations.

“Global climate change is forcing penguins to adjust their behaviour to avoid new predation risks while still locating enough of their own food,” said Grant Ballard.

The study’s results are important because how behavioural factors like these influence the survival of species has not yet been considered when understanding and conserving Southern Ocean food webs.

Source
Are penguins more fearful than hungry? 23 June 2011, PRBO Conservation Science

Polar Biology citation
Non-consumptive factors affecting foraging patterns in Antarctic penguins: a review and synthesis. Ainley, D.G and Ballard, G. Polar Biology, 17 June 2011.

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