The huddling is known as social thermoregulation, and penguins do it more often when temperatures plummet and winds get stronger. The most extreme examples of social thermoregulation, as the paper notes, are done by emperor penguins. They are the only animals that breed during the frigid Antarctic winter, and thus need to keep warm. The researchers found that emperor penguin huddles lasted from about 12 minutes to several hours, and individual emperor penguins spent an average of 50 minutes in a huddle. One theory as to why the penguins don't stay together longer because the huddles get too warm for them. In some cases, temperatures in the huddle reached as high as 99.5 degrees F (37.5 C), well above the 68 degrees F (20 C) the penguins can handle. And so huddles might break up to regulate this heat. In fact, once they had left a particularly hot huddle, some penguins were observed eating snow, possibly to lower their body temperature.