A pile of sleepy rabbit pups isn't just cute—it's good for rabbitkind. Newborn rabbits compete for their mother's milk, and successful pups grow stronger and are more likely to pass on their genes to the next generation. But sibling rivals will put aside their differences to protect each other from the cold, according to a study published this month in PLoS ONE. Using infrared cameras (right) and rooms that slowly cool from 23°C to 11°C, researchers found that when the temperature drops, less-than-5-day-old furless rabbit pups huddle to share heat. Such cooperation, like investors making a joint business venture, comes at a small private cost, as generating heat uses body fat that in turn uses up oxygen, and using too much oxygen can stunt a rabbit's growth. But by sharing heat, rabbits mutually ensure that their siblings don't have to use up too much energy to survive the cold, helping them all live on to contribute to future bunny generations.
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