It is extremely rare to see a chimpanzee give birth in the wild; the event has been observed only a handful of times. So when researchers studying chimps in the Mahale Mountains of Tanzania witnessed a female giving birth among her troop in December of 2014, it was a moment of surprise and excitement. Things soured quickly, however: almost as soon as the newborn had entered the world, a male chimpanzee of the same group grabbed it and disappeared into the foliage.

An hour and a half later, the researchers found the male eating the baby. It took him less than an hour to finish it.

The male chimpanzee, known as Darwin, holding the newborn infant (approximately 40 minutes after delivery). Image: Nishie & Nakamura

This behaviour – stealing and cannibalising an infant immediately after birth – has never before been seen in chimps.

One of the reasons that chimpanzee births are so difficult to catch in the act is that chimp mothers have a habit of going on “maternity leave.” When a female is about ready to give birth, she will typically disappear from the rest of her group and return weeks or months later with her newborn clinging to her.


In their new study, in addition to recording this startling case of baby-snatching, Hitonaru Nishie and Michio Nakamura of Kyoto University also looked over three decades of attendance records of this Mahale Mountains chimp group, and found that while it's not uncommon for female chimps to occasionally  leave the group, the longest absences were generally taken for this “maternity leave.”

For a while, primatologists have wondered why chimps would leave their companions behind to give birth alone in the woods, and now it seems they might have a clearer answer.

“[We] suggest that it functions as a possible counterstrategy of mother chimpanzees against the risk of infanticide soon after delivery,” the researchers state. It may be that this mother was young and inexperienced, unaware of the dangers of having her baby in front of the 20 other members of her group. And indeed, for her next birth, she left for about a month.

If it’s true that maternity leave exists to protect baby chimps from cannibals, it raises another macabre question: why is infanticide so common?

It’s not news that animals sometimes kill and eat babies of their own species, and even their own children. Young animals may occasionally offer a convenient source of food, and males of plenty of species – from apes to lions to dolphins – are known to kill the children of other males to remove competition and to bring the mothers back into oestrus so they can breed again. Other times, it may simply be the result of aggression.

To us humans, infanticide may seem like a gruesome and irrational act, and it can be easy to assume that there must be something wrong with baby-killing chimps. Such accusations were levied, for example, at the male chimp who killed a three-month-old of its same group in the Los Angeles Zoo in 2012, and also to the famous mother-daughter pair of Passion and Pom, observed in the wild by Jane Goodall as they worked together to kill at least three infants within their own troop.

But scientists have been studying chimps for years, and it seems infanticide is not at all uncommon. Many cases have been recorded across several chimpanzee groups, perpetuated not only by males, but also females, sometimes working alone and at other times cooperating on the grisly task. In some instances, these murders seem to be related to male competition or to female-to-male ratios within the group, but the reasoning is not always clear.

Footage from 2004 shows the aftermath of two different infanticides committed by the males of Uganda's Ngogo chimpanzee community. In the first clip a young adult male is seen cannibalising an infant, and in the second a late adolescent male holds and grooms a dead baby.

In fact, it has been suggested that this behaviour, so horrific from a human perspective, is common enough among chimpanzees to have affected their social evolution. Females with young tend to avoid the boundaries of territories, for example, where the babies may be at risk from patrolling males of neighbouring groups.

Chimpanzee “maternity leave” appears to be another behaviour that has come about as a result of widespread infanticide in the species. Humans and many other animals are often born surrounded by family and friends, but for chimpanzees, it seems mothers are better off giving birth in seclusion.


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