Huddle Up: the Surprising Physics of Penguin Movements

When male emperor penguins face the minus-58-degrees-Fahrenheit (minus 50 degrees Celsius), 120-mph (200 km/h) winds of Antarctic winters, the birds rely on their neighbors' bodies to keep themselves — and the eggs that they protect in a pouch near their feet — alive and warm.

Maintaining a massive huddle of thousands of penguins may sound fairly simple, but sticking together in a pack so large turns out to be quite complicated: When one penguin moves a single step, the rest must also move to accommodate the open space and stay warm. In this particular species of penguin, males play the unusual gender role of incubating eggs, so it is especially crucial that they maintain warmth during cold winters. 

Previous research has suggested that individual penguins within a huddle regularly make small movements roughly every 30 to 60 seconds, travelling between 2 and 4 inches (5 and 10 centimeters) with each step. But researchers haven't understood the physics behind how all of these moving parts stick together as a single unit.

Now, biologists and physicists based at the University of Erlangen-Nuremberg in Germany have collaborated to create mathematical models based on time-lapse camera footage of emperor penguins to try to understand the physics behind the huddles. [Video: Watch Massive Emperor Penguin Huddle Shuffle as a Wave]

The team's mathematical models showed that the huddles behave as waves instigated by any individual in the pack, no matter that individual's location. If two waves travel toward each other, they merge, rather than passing one another. Gaps just 2 centimeters wide (0.8 inches) appear to instigate a reorganization, in order for the penguins to stay warm, the team reports today (Dec. 16) in the New Journal of Physics.

Why penguins move so frequently and in such small steps remains unclear, though the researchers think the shuffles may help the birds rotate their eggs to keep them warm.

"It might be that the egg can get cold at the bottom and so the penguins have to rotate the egg every now and then," Gerum said. "This is just a speculation."

Emperor penguins are the only vertebrates on the Antarctic continent that breed during the coldest months of the year. 

While the model that the researchers created has the penguins moving in a straight line, the natural formation of the huddles often moves more in a spiral rotation, Gerum said. Next, the team hopes to create a mathematical model that recreates this more complicated rotational movement.

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