Four times a year, a female mongoose gives birth to her pups on the exact same night as more than half of the other females in her group; up to 10 females can give birth at the same time. The small carnivores aren't planning a massive birthday celebration. Rather, they're trying to ensure the survival of their pups. In tomorrow's online edition of Biology Letters, researchers report that mongoose litters born a day or two earlier than others were 30% more likely to be killed by adult female mongooses. These females don't want competition for their own kids, so they kill the pups while their mothers are out foraging. But if the litters are born together, all of the moms are out foraging at the same time—so there's no one left behind to kill the babies. Litters born later don't fare too well either; the pups have less time to grow and are thus more vulnerable when they leave the den. Similar scenarios in ancient human societies may explain why women often sync up their menstrual cycles if they spend a lot of time together.
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