Emperor penguins huddled by the thousands in antarctic colonies perform a subtle version of the sports crowd "wave" to say warm, researchers say.

What a human crowd will do visibly to celebrate, the birds do almost invisibly to stay alive, The Sydney Morning Herald reported Friday.

To successfully carry an egg through extreme midwinter cold, male birds gather in thousands-strong assemblies, packed in at a density of up to 12 birds per square yard, biologist Barbara Wienecke of the Australian Antarctic Division said.

A male emperor penguin must survive howling winds and temperatures of minus 45 degrees carrying an egg on his feet for about 110 days before the female returns from the sea to take over breeding duties.

Rather than jamming together in an uncoordinated mass, they gently push their neighbor in a traveling wave, Wienecke said.

Each bird moves forward in small steps every half minute or so, and gradually the wave travels through the whole huddle, she said.

Eventually each bird is pushed out to the edge of the huddle where it is most exposed to wind.

"Then they shuffle around from the windward side to the leeward side, and enter the huddle again," Wienecke said.

The larger the huddle the longer the relief from the cold, researchers said, noting that some huddles can contain more than 20,000 birds.

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