Emperor penguins keep warm in the harsh Antarctic winter by huddling together. But how do penguins on the outside of the huddle, get to the inside, for their share of the warmth?

It’s a question that’s baffled scientists for years. But now, thanks to time-lapse imagery, scientists have found that the penguin huddle moves in a wave pattern every 30 to 60 seconds.

‘All the penguins in row one might take small steps to the right by 5 or 10 centimetres simultaneously, and then the penguins in the second row do the same, just afterwards,’ says seabird ecologist Dr Barbara Wienecke, of the Australian Antarctic Division.

‘Over time, these small movements lead to a large-scale reorganisation of the huddle.’

The research, which was published in the journal PLoS ONE this week, was led by PhD student Daniel Zitterbart of the University of Erlangen-Nuremberg, during a winter at Dronning Maud Land.

Zitterbart took time-lapse images every 1.3 seconds for four hours and then used software that he’d designed to follow the movements of penguins within the huddle.

He found that as temperatures dropped to −43°C the penguins aggregated in multiple huddles. These huddles remained motionless for most of the time and were tightly packed, with some 21 penguins per square metre. Every 30 to 60 seconds the huddle moved by small 5–10cm steps in a coordinated manner — much like a Mexican wave — before tightly packing together again.

The paper’s authors say the small, regular steps achieve three things: they allow for the highest packing density, to ensure warmth; they ensure a forward motion of the entire huddle; and they lead to a slow reorganisation of the huddle, without disturbing the penguins in the centre of the huddle.

Time-lapse video of penguin huddle formation and the travelling waves can be viewed with the scientific paper on the PLoS ONE website.