Penguins are remarkable birds who manage to survive in some of the harshest of environments on earth. The survival techniques of Emperor penguins have long intrigued scientists who have just made another interesting discovery about how they manage to keep warm.
To live in temperatures below -50°C and gale-force winds above 180 km/h while fasting during the Antarctic winter, Emperor penguins gather in tightly packed huddles. It is crucial that the huddle structure is continuously reorganised to give each penguin a chance to spend sufficient time warm inside the huddle, compared with time spent cold on the periphery. But until now we did not know how the colder penguins on the outside of a huddle move to the inside when the animals stand packed so tightly that any movement seems impossible.
A physicist from Germany recently spent a winter in the Antarctic, making high-resolution video recordings of an Emperor penguin colony. Together with a biophysicist from Germany, a physiologist from the US, and marine biologist from Australia, they found that penguins in a huddle move collectively in highly coordinated periodic waves to continuously change the huddle structure. This movement allows animals from the outside to enter into the tight huddle and to warm up while at the same time keeping the huddle packed.
The researchers made the discovery by tracking the positions of hundreds of penguins in a colony for several hours. The periodic waves are invisible to the naked eye. They happen every 30–60 seconds and travel with a speed of 12 cm/s through the huddle.
All penguins make small steps that travel as a wave through the entire huddle. Although small, over time they lead to large movements that have been likened to dough during kneading. Over time, these movements lead to large-scale reorganization of the huddle. The authors compare the formation of a huddle to "colloidal jamming" and the periodic waves to a "temporary fluidization."
The German physicist, Daniel P. Zitterbart, is currently developing a remote-controlled observatory to study penguins all year round. He hopes to witness the reversal of the dramatic decline in penguin colony sizes that is occurring in all areas of the Antarctic.
We wish Mr Zitterbart the best of luck with his important work studying the fascinating natural behaviour of these admirable animals in the wild.