If you're in stop-go traffic, you're probably pretty unhappy about it. If you're a male penguin balancing an egg on your feet in the freezing Antarctic, that traffic jam is probably keeping you alive.
Scientists studying huddles of emperor penguins in Antarctica have discovered that waves of movement travel though huddled masses of flightless birds rather as they do through cars stuck on the freeway during rush hour - but in ways that keep the birds warm as they incubate their eggs.
Emperor penguins are the only vertebrate species that breed during the Antarctic winter, and they face freezing winds that blow as fast as 200km/h in an icy landscape that can be as cold as 50 degrees Celsius below zero. So they huddle together against the harsh elements - and together, their bodies can raise the temperature within two hours to as high as 37 degrees above zero.
At first glance, the penguins may not appear to move much. The males probably can't run anywhere in a rush, in any case: The fathers-to-be cover their eggs with feathered skin known as a brood pouch, with the eggs resting on top of their feet.
"If you look at a penguin huddle in real time, you hardly see any movement at all - they are all standing very still," said Richard Gerum, a physicist at University of Erlangen-Nuremberg in Germany and first author of the study published in the New Journal of Physics.
But watch this huddle of shuffling penguins long enough, and there emerge distinct waves of motion through the feathered masses as one penguin takes a step and the rest follow. It's a way of maintaining order, Gerum pointed out.
"When a big human crowd is together, there can be accidents," Gerum said. "And this is something that never happens in a penguin huddle."
So although the emperor penguins don't dance like the characters in the 2006 animated film Happy Feet, they still perform some pretty fancy footwork.