长颈鹿通常不会对和谁组成群体很挑剔，但一项新的研究称，雌性长颈鹿在生育之后就会开始变得挑挑拣拣。在2010至2011年间的几个月里，研究人员对坦桑尼亚卡塔维国家公园的一群长颈鹿进行了持续追踪。他们确定了三只在此期间分娩的雌性长颈鹿，记录下了它们群居方式的清晰变化。在分娩前，雌长颈鹿同随机的长颈鹿，无论雌雄，组成灵活的鹿群，群的构成定期变化。但在分娩之后，雌长颈鹿组成了严密的群组，仅包含其它长颈鹿母亲和她们的幼崽(如图)，研究团队本月在《非洲生态学期刊》上报告了这一研究成果。在极少数情况下，科学家们会看到雄性长颈鹿也加入到这个鹿群中，但这些雄长颈鹿呆了两天就离开了。论文作者认为，这很可能是雄长颈鹿在寻找伴侣的情况。长颈鹿幼崽在出生头六个月中无法长距离行走，这使得它们成为天敌易攻击的目标。研究人员说，这种仅包含母鹿和小鹿的鹿群代表着更稳定的群体，在这个群体中的长颈鹿几个月黏在一起。这种鹿群还可以让长颈鹿母亲们能在其中一些雌鹿外出觅食的同时更好地照顾小鹿。但是，为什么这种鹿群中没有雄鹿?论文作者认为，雄性长颈鹿对保护鹿群不感兴趣，而更愿意把时间花在觅食和交配上。虽然其它物种已知也会组成这种类型的群体，但只有抹香鲸会在分娩后改变自己的群居行为。
原文链接：How is a giraffe like a sperm whale?
原文摘要：Giraffes usually aren’t choosy about who they hang out with, but after they give birth females start to get selective, according to a new study. Researchers followed a group of the ungulates in Katavi National Park in Tanzania for several months between 2010 and 2011. They identified three female giraffes giving birth during this period and recorded clear changes in their herding pattern. Before giving birth, females formed flexible herds with random individuals, male or female, changing herd composition regularly. But after giving birth, the females formed tight groups composed of other mothers and their calves (pictured), the team reports this month in theAfrican Journal of Ecology. On the rare occasions the scientists saw males joining this group, the guys left after a couple days. The authors think that these were likely cases of males looking for a mate. Calves are not able to walk long distances for their first 6 months, which makes them easy targets for predators. This type of mother-calves-only herd represents a more stable group of individuals that sticks together for several months, the researchers say. It also allows the moms to take better care of the young ones while some of the females take a foraging break. But why aren’t males part of these types of herds? The authors think that males are just not interested in protecting herds, but rather spend their time foraging and mating. Although such types of herds are known for other species, only sperm whales are known to change their herding behavior after giving birth.
