The cold that makes the huddle necessary
Wind chill on the Antarctic breeding grounds of emperor penguins can drop to -60°C. A lone penguin standing in that wind loses body heat faster than its metabolism can replace it. The emperor penguin's core body temperature sits around 37°C, roughly the same as a human's, and the gap between that internal warmth and the surrounding air is one of the largest any warm-blooded animal routinely bridges.
