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Gorilla mothers: No need for help, thank you

Gorilla mothers have very strong bonds with their infants, and provide complete care for them during their first few years, starting with carrying them everywhere against their chest, and then later having them ride on their backs. Of course, this takes a lot of extra energy in traveling with their groups every day, in addition to feeding the nursing youngsters.

Compared to humans, gorilla moms rarely allow other group members to handle or carry the infant, though sometimes we do see other individuals in a group lending a hand. But this had not been closely studied, and our scientists theorized that such non-mother handling would be most frequently carried out by younger females who had not yet given birth, and were thus practicing their skills, or by maternal relatives, such as sisters or aunts.

Luckily, the large, long-term database of the Fossey Fund has just the information needed to test these hypotheses. In a paper published last month in the American Journal of Physical Anthropology, former Karisoke Research Center scientist Dr. Cyril Grueter and collaborating scientists analyzed eight years of Karisoke data, covering 13 gorilla groups. In 25,600 hours of observation, they found 1,240 instances of infant handling by females other than the mothers, which makes this a relatively infrequent social behavior.

What did we learn?
Non-mother handling of mountain gorilla infants is less frequent than in other wild primates that have been similarly studied. This may be because bonds between adult females in gorillas are weaker than those in many other primates.   But several of the findings were consistent with what has been seen in other primate studies — specifically, that infant handling occurred more often by females related to the mothers and also by females who had not previously had their own offspring. The latter is consistent with the “learning to mother hypothesis,” which assumes that such handling gives young females a chance to practice mothering skills.

One question that still remains is about the potential benefits of infant handling.  For mothers, does it provide them with the opportunity to feed more freely without having to hold their infants? Or does it relieve some of the energetic costs of transporting their infant? For the handler, are they more successful when they become mothers of their own if they have had the opportunity to handle an infant?  These are some of the most intriguing questions that still need to be answered.

And what about monkeys?

In a different study recently published in Science Advances, Dr. Grueter studied golden snub-nosed monkeys in central China, and found that these monkey moms were quite likely to accept help from other mothers, including allowing their infants to nurse from non-mothers who also had infants. Usually the non-mothers were related and it seemed that these additional doses of milk really benefited the infants in terms of their survival in this harsh environment.