Grieving baboons find shoulder to cry on
Female baboons that suffer the loss of a close friend or relative turn to other baboons for comfort and support, according to a new study.
The study encompasses 14 years of observing over 80 free-ranging baboons in Botswana's Okavango Delta.
It provides the first direct evidence that certain animals mourn the loss of individuals, even when the rest of their social group remains intact.
The findings also suggest that friendship may be just as important to some primates as it is for humans.
Researchers were particularly struck by the behaviour of one female chacma baboon (Papio hamadryas ursinus) named Sylvia.
She was described as "the queen of mean" and disdainful of other baboons until she lost her daughter, Sierra, to a lion kill.
"In the week after Sierra died, Sylvia was withdrawn," says Dr Anne Engh, who led the project.
"When the other females were grooming and socialising, she tended to sit alone and rarely interacted even with her other relatives."
Engh, a postdoctoral researcher in the Department of Biology at the University of Pennsylvania, adds:
"After a week or two of moping around, Sylvia suddenly initiated grooming with several low-ranking females. I think that they were as surprised as I was; they seemed awfully nervous at first. Eventually, Sylvia settled into close relationships with a very low-ranking female and with Sierra's daughter, Margaret."
Engh says that grooming is a friendly behaviour similar to two human friends chatting over a drink.
The activity seems to relax the participants to the point where it can lower stress hormone levels. Those levels rise in humans and baboons after a close friend or relative dies.
The researchers measured a group of such hormones, called glucocorticoids, in Sylvia and 20 other females. Baboons that experienced losses had elevated levels of the hormones after the deaths.
In humans, this is associated with bereavement, so it is likely that baboons also grieve their dead.
The mourning animals then widened their social circles by approaching and grooming other females, even those that were beneath them in rank.
This appeared to help them cope with losses, since stress hormone levels significantly dropped afterwards.
The discovery, outlined in a recent Proceedings of the National Academy of Sciences paper, underscores the importance of friendship.
"Humans and baboons who are more socially integrated have lower glucocorticoid levels," says Engh.
"Both the human research and our results highlight the importance of friendly social relationships in reducing stress.
"Female [baboons] usually have one or two close female friends that usually devote a large proportion of their grooming to each other, and they seem to enjoy spending time close together."
Engh also mentions that friendships form between male and female baboons. For those relationships, the female often grooms the male, while the male protects the female, and any infants that she might have, from predation and bullying baboons.
No surprise there
Brian Craft, lead keeper at the Oakland Zooin California, says that he was not surprised by the findings.
"Advanced relationships are seen in chimpanzees, bonobos, as well as baboons and other multi-social troops," Craft explains.
"Friendships, which may help to ease stress after deaths, can be beneficial to the troop as a whole, as they keep it cohesive. It also appears that friend selection among baboons and other primates is somewhat of a choice, as for humans, and is not just instinctive behaviour."