Baboons Grieve Over Lost Relatives, Study Suggests
for National Geographic News
|February 21, 2006|
Sylvia, a 23-year-old baboon living in the Okavango Delta of Botswana, Africa, is one of the highest-ranking members of her troop.
In the past, she generally expressed nothing but contempt for other troop members, except for Sierra, her grooming companion.
But when Sierra was killed by a lion, Sylvia went into what could be described as mourning. She then appeared to seek solace in the form of mutual grooming from females whom she had previously seemed to consider beneath her attention.
Researchers working with Sylvia's troop now say they have physical evidence that Sylviaand other female baboonsexperience grief.
"In general, female baboons have closer relationships than males do," said Anne L. Engh, a postdoctoral researcher in biology at the University of Pennsylvania in University Park.
"Male baboons don't cooperate socially and don't form friendships with each other. So I wouldn't expect them to mount much of a stress response to the demise of another male," said Engh, who was the lead author on the study.
In addition to observing differences in behavior, the scientists measured the levels of stress hormones in female baboons' feces.
They found that females who had lost a close relative showed significantly higher levels of the stress hormone glucocorticoid than unaffected animals in the same reproductive state.
What's more, seeking companionship after the loss seemed to lower the grieving animals' glucocorticoid levels back to normal levels.
Engh and colleagues report the findings in a recent issue of the journal Proceedings of the Royal Society B.
"Queen of Mean"
According to Engh, Sierra was Sylvia's daughter, "and Sylvia usually didn't interact with other females. If she did, she wasn't very friendly." (Wallpaper: mother baboon and child.)
But in February 2004 lions killed Sierra and a male she was consorting with.
Predation by lions and leopards is the most common cause of death among Botswana's baboons.
Lions attack in groups of three or more, scattering the baboons into smaller groups that remain apart for several days before they reunite.
The researchers found that the baboons' stress-hormone levels were higher during these temporary separations.
They also found that predation is especially stressful for females whose close relatives are killed.
Female baboons do most of their grooming with close kin, so researchers speculated that Sierra's death would lead to a decrease in the amount of grooming Sylvia engaged in.
But the opposite turned out to be the case.
"For a week or two [after Sierra died] Sylvia sat alone staring at her feet and really didn't interact with the others very much," Engh said.
The researchers didn't waste any sympathy on the seemingly grieving baboon.
"We don't feel that sorry for Sylvia, because she has been known as the Queen of Mean her whole life," said. "She's very high ranking and very nasty to the lower-ranking females.
"But what was very surprising was that after about two weeks she started being really nice to lower-ranking femalesquite a change in behavior.
"She started initiating grooming with them, and settled into a friendly relationship with a low-ranking female she'd never given the time of day to before."
The scientists also found that Sylvia's glucocorticoid levels, which had tripled after Sierra's death, were down to normal by the second month after the incident.
Frans de Waal is a professor of primate behavior at Emory University in Atlanta, Georgia, and was not involved in the study. He says this hormone research in baboons is "wonderful work."
"This is an important study, the sort of thing that needs to be done more often," de Waal said.
"We have a lot of anecdotal evidence of grieving in primates, especially with mothers who lose offspring. They carry around the infant until the body falls apart, or go into depression, stop eating, sit in a corner the whole day.
"But this is the first study I've seen of traumatic social experiences where the researchers measured the impact hormonally."
De Waal also pointed out one aspect of the study that the researchers themselves did not emphasize.
"There's an absence of response by the other members of the group. In monkeys you don't find evidence of sympathy. You do in apes and, of course, in humansalso in elephants. They respond to the distress of others."
But with the troop of baboons, de Waal added, there is "an absence of an empathic environment."
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