Massive huddles of male Emperor penguins are crucial to keeping warm during Antarctica’s brutal winter while they incubate their eggs.

These tightly packed penguins shuffle en mass every 30 to 60 seconds, reordering themselves so every individual gets to cycle through the warm, central part of the huddle.

The trick with these groups is to get the packing just right. If the penguins are too loosely arranged, they won’t stay warm enough, said Daniel Zitterbart, Barbara Wienecke, James Butler and Ben Fabry in a June 1 study in PloS One. But if they’re too tightly jammed together, they can’t rearrange themselves, and animals on the edge of the huddle won’t get a chance to warm up.

By taking small, 2- to 4-inch steps every minute or so, the penguins achieve maximum packing density. It’s like tapping on a can of flour to jiggle everything into the bottom.

But the shuffling also results in a wave of movement that rolls through the group and rotates every bird through the warmest parts of the huddle. Penguins can join the group on one end, cycle through the huddle and exit on the other end.

This creeping movement also means that different groups can merge into larger huddles.

The international team of researchers kept track of emperor penguin groups near a German research station in Antarctica using time-lapse photography. While charting the path of individuals over a four-hour period, the authors found that when the huddles remained still, they were tightly jammed. But once the shuffling wave started through the group, individuals ended up creeping their way through the huddle.

The authors found that individual penguins don’t change their position relative to their neighbors, nor do they force their way into or out of a huddle. The small steps the birds take are sufficient to move everyone around in a coordinated fashion.

The scientists still don’t know if one or more penguins start these waves of movement, or whether they follow any kind of hierarchy among individuals.

Image: Glenn Grant/National Science Foundation. Video: Daniel P. Zitterbart/PLoS One.

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Citation: “Coordinated Movements Prevent Jamming in an Emperor Penguin Huddle.” By D. P. Zitterbart, B. Wienecke, J. P. Butler and B. Fabry.PLoS OneVol. 6 No. 6, June 1, 2011. doi: 10.1371/journal.pone.0020260.