Saturday, 31 Oct 2020

Antarctic penguins are ‘happier with less sea ice’, scientists find

Antarctica’s most common species of penguin is happier when there is less sea ice, researchers have discovered.

Adelie penguins can travel more by swimming in ice-free conditions, and access food more easily, a study found.

Polar biologists have known for some time that penguins tend to see population increases during years of sparse sea ice but they did not know why – until now.

The birds also suffer massive breeding failures in the years with the greatest growth of sea ice.

Researchers with Japan’s National Institute of Polar Research electronically tagged 175 penguins with GPS devices and video cameras across four seasons with different sea ice conditions.

This allowed them to track penguins on their trips, categorise walking, swimming and resting behaviour, and estimate the amount of prey captured during dives.

Yuuki Watanabe, from the National Institute of Polar Research, said: “For penguins, swimming is a whopping four times faster than walking.

“They may be sleek in the water but are pretty slow waddlers overland.

“It turns out that these penguins are happier with less sea ice.

“This may seem counter-intuitive, but the underlying mechanism is actually quite simple.”

When there is heavy sea ice, Adelie penguins have to walk – and sometimes toboggan – a long way to find cracks in the ice in order to access the waters where they hunt, taking sometimes quite lengthy rests along the way.

But when there is less sea ice, the birds can dive anywhere they want, often just entering the water right by their nests.

Scientists say this is more energy and time efficient and it expands their foraging range.

It is also likely to reduce competition with other penguins for prey and allows them to catch more krill – the penguin’s main food source.

Less sea ice also means more sunlight entering the water, leading to larger blooms of the plankton that the krill feed on.

But this only applies to the penguins that live on the main “continental” part of Antarctica.

The opposite happens to the penguins that live on the thin Antarctic peninsula that sticks out from the continent or live on its islands.

The study, published in Science Advances, found that the penguins may have expended an average of 15% to 33% less energy per trip compared with ice-covered seasons, putting that saved energy into growth and reproduction.

In recent decades, Antarctica has experienced a steady increase in the extent of its sea ice, even as the Arctic has suffered through a marked decrease, the researchers said.

But this is not expected to last much longer due to climate change, with Antarctica also projected to see a decline in its sea ice.

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