New, sped-up video of an emperor penguin huddle in Antarctica shows the group takes small steps, creating a wave. Researchers say the undulations ensure each penguin a turn in the middle of the cluster, which helps the birds keep warm.

When the temperature is as cold as minus 50 degrees Fahrenheit, it helps if there’s a warm body nearby.

Emperor penguins in the Antarctic are known to huddle together for warmth. But what we didn’t realize was that they were creating a ‘wave’ when new penguins joined the huddle, and that wave helped move the huddle en masse.

Physicist Daniel Zitterbart from the University of Erlangen-Nuremberg in Germany recorded high-resolution time-lapse images of the huddle near the Neumayer Antarctic Research Station. They were then speeded up to see what was happening.

As penguins move in, generally from the rear, penguins in the huddle make small steps in a formation, to help the tightly formed mass remain intact.

Zitterbart and his colleagues point out that it is crucial that the huddle is continually reorganized to give each penguin a chance to spend sufficient time inside the huddle, compared to time on the periphery.

The ‘wave’ is created by the small steps, estimated at just 2 to 4 inches. The researchers suggest those steps serve three purposes: first, to keep the pack as dense as possible; second, it leads to forward motion of the entire huddle; and thirdly, over time, leads to its reorganization. Separate smaller huddles can also merge into larger clusters.

The Emperor penguins in these videos are all male. And most carried an egg on his feet. The females had not yet returned to the colony.