Monkey: When in Rome…

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Study: Monkeys ape the behavior of their group

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Vervet jumping from one green, leafy branch to another with tail outstretched and blue sky background.

Image ©Erica van de Waal
A young vervet monkey jumps between limbs. The food preferences of vervet monkeys can be transmitted to members who join their groups.

A field experiment in South Africa finds that vervet monkeys change their taste in food when they join a new group, providing further evidence for “social learning” in animals. When the experiment started, monkeys were fed blue or pink corn. One color had the usual taste, but the other was politely described as “highly distasteful.”

That quickly taught the monkeys a lesson on palatability.

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Seven light grey vervets huddle around two plastic boxes on ground, eating only from the box on the left.

Image © Erica van de Waal
Monkeys in this group prefer corn that’s dyed pink.

The researchers came back four months later to observe what newborns were eating. No shocker: they followed mom’s advice regarding corn color, even though both colors now tasted the same.

Then came the interesting part. As vervet guys mature, they migrate and join new groups. Intriguingly, 10 of the 15 migrant males immediately changed their preference to match the culture of the new group; four others had to wait to switch until the dominant males had eaten their fill.

“We designed the study for infants, which is why we had the four-month gap, so the babies would be ready for solid foods,” says first author Erica van de Waal, a post-doctoral researcher at St. Andrews University in Scotland. “But when we followed the male migrations, Wow! This monkey was trained to eat pink corn, and… to see him join the new group who all eat blue, and he decides, ‘No, I have to eat blue.'”

Video © Erica van de Waal
Vervet monkeys from this group were trained to eat pink corn even though both colors were equally palatable. What’s with the “eat-and-run” activity? Those are young monkeys, apparently a bit fearful of the adults who are dominating the food trough.

(Tactical note: The researchers tested both combinations. For half the groups, pink started out as yucky, for the other half, blue started out tough on the tongue.)

Mother knows best

Following the local lead has obvious evolutionary benefits, says van de Waal. “In a foraging diet, it’s really important” to benefit from the local knowledge.

Because females stay home on the range, they have enough local knowledge to survive. Not so for the moving man, van de Waal says. “He may see a new species of tree, or the toxic composition of edible fruits will change. They need the best local information to survive in the new environment.”

That’s especially true because males make multiple migrations, and thus seldom become experts in the local restaurant scene. “You could think that a dominant male that was in a group for 10 years would have as much knowledge as the females, but these males change groups a lot,” van de Waal says.

Although both colors had the same taste in the new location, even after migrant males tasted their previous preference, van de Waal says, “They still thought, ‘If the locals want that one, it must be better.’

“We know that vervet monkeys are opportunistic and adaptable, they have spread across Africa, so as soon as they found that both foods taste the same, we thought the ratio would drop to 50-50,” van de Waal says. “Not at all. Even the ones with previous knowledge adopted the new normal color.”

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Spiky green whole fruit with sliced version resting in front, showing a soft yellow inside with a row of images showing below the fruit, showing three people sitting in restaurant, faces animated with surprise, tasting a milkshake.

Durian fruit from Shutterstock and people eating durian from Renée S. Suen
The durian is a cultural icon in much of Asia and a rite of passage for people trying to accustom themselves to a new culture. See reactions to taste-testing a durian milkshake above.

Shocker: This guy didn’t want advice

What about that 15th male, who remained his allegiance to the corn color of his youth? “It’s kind of strange,” says van de Waal. “He entered a group where the dominant male had disappeared, he was a big, strong adult male, a full adult, and he directly became the dominant male, and did not seem to care about what the others were eating.”

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Three young and one mature vervets eat pink corn from a plastic box on ground.

Image ©Erica van de Waal
This adult male is eating pink corn with juveniles from his group.

And that suggests that the survival advantages of changing food preferences to suit the “culture” in a new location may not fully explain the results, van de Waal says. “Maybe it confirms there is something social going on.”

At any rate, you can’t fool the true experts, she says. “The females did not try the color he was eating. The dominant females are always conservative; he did not influence the dynamic of the group.”

On the other hand, “This is sample of one,” says van de Waal. “Maybe he is just a stupid male that does not care what the others are doing.”

– David J. Tenenbaum

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Terry Devitt, editor; Emily Eggleston, project assistant; S.V. Medaris, designer/illustrator; David J. Tenenbaum, feature writer; Amy Toburen, content development executive

Bibliography

  1. Potent Social Learning and Conformity Shape a Wild Primate’s Foraging Decisions, by E. van de Waal et al, Science, 26 April 2013.
  2. Monkey facts: learn more about vervets
  3. More monkey socialization: BBC documents vervet consumption of alcohol
  4. How smelly is durian?
  5. Vervet monkey genomics