With thousands of Emperor penguins (Aptenodytes forsteri) huddled close together for warmth on the ice sheets of Antarctica, there seems bound to be some competition for a toasty spot near the middle. But these enormous clusters manage to bring each penguin in for a chance to warm up—all without causing a dangerous crush. How do they do it?

A team of researchers positioned a high-resolution, time-lapse camera to capture the surprisingly subtle and complex movement dynamics of one penguin pack near the Neumayer Antarctic Research Station. An analysis of the video revealed the coordinated movements that were invisible to the human eye in real time.

In the sped-up video, they could see that the "Emperor penguins move collectively in a highly coordinated manner to ensure mobility while at the same time keeping the buddle packed," the researchers noted in a new study, which published online Wednesday in PLoS ONE. "Every 30-60 seconds, all penguins made small steps that travel as a wave through the entire huddle. Over time these small movements lead to large-scale reorganization of the huddle." And the reshuffle takes time, with each step measuring just five to 10 centimeters.

The wave pattern was not unlike that of a a sound wave traveling through a fluid, pointed out the research team, which was led in part by Daniel Zitterbart, of the Department of Physics at the University of Erlangen-Nuremberg in Germany. "In general, individual penguins do not change their position relative to their neighbors, and they do not force their way in or out of a huddle," they noted.

In dense crowds, people also tend to move in waves. But we are not so orderly, which often leads to chaotic crushes and occasionally death. "Why these waves are uncoordinated, turbulent and dangerous in a human crowd but not in a penguin huddle remains an open question," Zitterbart and his and colleagues wrote. Another lingering unknown is whether the evenly paced penguin waves are the work of a few leaders, like enthusiastic fans at a baseball game, or whether each penguin "follows a well-defined hierarchy among group members, similar to the collective behavior in pigeon flocks."

But however the wave gets going, it seems to do the trick. Most of the penguins featured in the film were carrying an egg and were in the midst of fasting—all the while facing temperatures of -33 to -43 degrees Celsius with howling August winds of 8.3 meters per second.