Why do penguins huddle together?

Emperor penguins breed during the Antarctic winter, when temperatures can plunge below minus 40 degrees Celsius and winds can exceed 140 km/h. To survive, hundreds or thousands of birds pack tightly into a huddle, dramatically reducing the surface area exposed to the cold and trapping warm air between their bodies. Inside a dense huddle, temperatures can climb above 20 degrees Celsius even as the outside stays deep below freezing. The huddle is not static: penguins take turns moving from the warm centre to the cold outer edge and back, so no individual is stuck in the cold for too long. This cooperative behaviour lets males incubate their eggs through months of darkness while fasting.