Emperor penguins stay in large huddles to stay warm in frigid Antarctica; new observations found the animals' movement is similar to a rush hour traffic jam.
A research team used a mathematical model to map out how the penguins interacted with each other, an Institute of Physics news release reported.
The researchers found individual penguins needed to move less than an inch (two centimeters) in order for their neighbor to react and step closer to maintain the protective huddle.
The movements "flow through the entire huddle like a travelling wave and play a vital role in keeping the huddle as dense as possible," the news release reported. The system can also help multiple smaller groups meld together into one.
The team determined in a past study that the movement is not constant, but takes place every 30 to 60 seconds.
"Our previous study showed how penguins use travelling waves to allow movement in a densely packed huddle, but we had no explanation as to how these waves propagate and how they are triggered," Co-author of the study Daniel Zitterbart, from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), said.
In order to confirm their findings the team compared a mathematical model (that had previously been used to study traffic jams) with video of a real penguin huddle.
The researchers found the difference between a penguin huddle traffic jam was that the movement of the penguin group usually came from an individual that created a gap that needed to be filled in, called a "threshold distance."
The estimated threshold distance (two centimeters) is about "twice the thickness of a penguin's compressive feather layer," which suggests the penguins strive to touch feathers without putting too much pressure on each other.
"We were really surprised that a travelling wave can be triggered by any penguin in a huddle, rather than penguins on the outside trying to push in," Zitterbart said. "We also found it amazing how two waves, if triggered shortly after each other, merged instead of passing one another, making sure the huddle remains compact."
Male emperor penguins are responsible for incubating their eggs in the negative 58 degrees Fahrenheit (negative 50 degrees Celsius) temperatures during breeding season.