Penguins Do the Wave to Stay Warm

By huddling together and using synchronized movements, the birds can stay warm in the coldest environment on Earth.

THE GIST

Emperor penguins have their own version of "the wave" which they use to stay warm.

A wave of movement passes through a huddle of penguins about every 30 to 60 seconds.

The movement was discovered using software designed to follow tagged cancer cells.

Emperor penguins huddled together against the cold are using coordinated waves of movement to stay tightly packed together.

The surprising finding has emerged from a detailed analysis of penguins near the Neumayer Antarctic Research Station, which is reported in this week's edition of PLoS One.

He took time-lapsed images every second over a four-hour period, and then used software, which he had previously designed to follow tagged cancer cells, to enable him to follow the movements of penguins within the huddle.

Amazingly he found that a wave of movement was passing through the penguins, roughly every 30 to 60 seconds.

"All the penguins in row one might move to the right by 5 or 10 centimeters (two or four inches) simultaneously, and then the penguins in the second row would do the same, just afterwards", says Barbara Wienecke, a seabird ecologist at the Australian Antarctic Division, who is one of the co-authors.

The penguins in the huddles were all males, each balancing an egg on their feet as they endured two months of fasting in the Antarctic winter to incubate their eggs.

"Emperor penguins are the most superbly adapted bird to these conditions. They are the only warm-blooded animal that breeds in the Antarctic winter," says Wienecke.

The birds form into huddles when it becomes very cold, and during storms. All the birds in a huddle face the same way, and pack together extremely closely, with as many as 10 to 12 of the huge birds per square metre, according to Wienecke. Huddles can contain hundreds or even thousands of birds.

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"The wind-chill factor is just enormous. Huddling saves an awful lot of energy", she adds.

But why are the birds doing the wave as they huddle?

Zitterbart says that the waves are a coordinated movement, which keeps the huddle moving.

"By keeping the huddle in motion, you get a denser packing", he says. "The small steps the penguins take compact the huddle, similar to the tapping of a bag of loosely packed granular material".

Wienecke thinks there might also be physiological reasons for the waves. "It may improve their blood circulation," she says. "Standing still for hours would be very difficult."

Zitterbart says it is not clear whether there are 'pacemaker' penguins initiating the coordinated movements or whether the waves just arise naturally by all the penguins following a simple set of behavior rules.

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