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Rodrigues compares behavior of captive chimpanzees, bonobos in recent publication

Beckman Institute Postdoctoral Fellow Michelle Rodrigues conducted a study observing bonobos and chimpanzees in captivity. The resulting paper will be published in a special print edition of Primates that focuses on social network analysis in primates. Rodrigues found differences in the social bonds and behavior of the primates in captivity that varies from those in the wild.

Published on July 12, 2018

If it’s true that your character is mirrored by the company you keep, then Beckman Institute Postdoctoral Fellow Michelle Rodrigues might be considered nurturing, charming, sociable, curious, irritable, mischievous, easy going, jealous, and dramatic. That is how she describes the range of personality traits in the primates she studies.

“I just love watching primates,” Rodrigues said. It shows in her dedication to the long hours it takes to observe and record their behavior and interactions, and then analyze the wealth of data.

 Rodrigues and Lady.
Watching the primates for such long periods of time, Beckman Institute Postdoctoral Fellow Michelle Rodrigues not only came to know their faces, but learned their personalities. Many primates ignore zoo visitors, but after Rodrigues’ presence over several months, some of her subjects displayed behavior that they wanted “to be her friend.” In the photo, Rodrigues poses with Lady, who she describes as a “female bonobo with perfect hair.”

For her recent paper, “Comparative Social Grooming Networks in Captive Chimpanzees and Bonobos,” Rodrigues observed captive bonobos at the Columbus Zoo, in Columbus, Ohio (summer 2013) and captive chimpanzees at the North Carolina Zoo, in Asheboro, North Carolina (summer 2014). The study premiered online and will be featured in a special print edition of Primates that focuses on social network analysis in primates. Rodrigues began the project after earning her Ph.D. at Ohio State University, completing preliminary data analysis in 2015-2016 so she could present the research at the joint International Primatological Society-American Society of Primatologists meetings in August 2016. She did additional analysis prior to submitting the research to Primates in January.  

“The study looked at the social bonds or friendships in male and female chimpanzees and bonobos, who have a similar social structure but behavioral differences in the wild,” Rodrigues said. “Chimps tend to be a lot more male centric—stronger male bonds and they are more aggressive. Female bonobos, on the other hand, are more affiliative and friendly than female chimps. They tend to have female-centric societies and are more peaceful. There’s a lot that’s made about that difference. And part of it is due to ecology, specifically where they get their food.”

According to Rodrigues, the ecology of each species varies in the wild. “Chimps, who rely primarily on ripe fruit, will often have females break off from larger mixed-sex subgroups or create smaller subgroups with other females with offspring because they need a lot more nutrition for their babies. Socializing with too many individuals means more competition for the food,” she said. “The bonobos’ environment tends to also include terrestrial herbaceous vegetation, which is basically yummy, nutritious leafy food that is more widespread, which means more animals can feed in the same area. So it has been hypothesized that the differences in these two species have emerged from the ecological differences.”

At the zoo, food is provided. So studying chimps and bonobos in a captive environment demonstrates the sex differences in social bonding in each species without the ecological constraints. Rodrigues was not surprised by the results because she hypothesized that these sex differences would be less pronounced in captivity, where they do not have ecology limiting their ability to socialize.

 Chimps grooming.
For her research, Michelle Rodrigues observed captive chimps and bonobos at different zoos. Primates in captivity do not have to worry about getting enough food, so they have a lot more free time to spend socializing. Pictured, chimpanzees grooming at the North Carolina Zoo. Photo by Michelle Rodrigues.

 “I wanted to see if those same kind of sex-typical differences in friendships actually happen when ecology isn’t limiting who they can hang out with,” Rodrigues said. “And basically, the bottom line is males and females are socializing with each other (more in captivity). When we look at social networks, females and males are occupying similar positions.”

Rodrigues hypothesized other factors may affect the behavior. “Captive-born bonobos have the most central social network positions. But, in that particular group, it also appears that group residence (how long they’ve been in the group) is important,” she said. “The wild-born bonobos are the ones that formed the core of that group originally and have been together the longest. The four core group members include two males and two females. Interestingly, they are all mid-to-low-ranking, so they do not have the most power, but nonetheless seem to be the most popular.

“One possible interpretation is that there is something about captive borns that they don’t have the same social skills, but I believe that it’s the group residence that is important. (This small group) has been together a very long time. They are the oldest and may sort of be the group elders.”

Rodrigues was the sole researcher collecting the data, which was done from public observation areas at each zoo, for safety reasons and to minimize researcher interaction with the subjects. To gather the data, she would focus on one subject for 30 minutes, recording on a check sheet every two minutes what activity they were engaged in, who the nearest neighbors were (within 3 meters), any social behaviors, and who they were interacting with.

Once all the data had been collected, it was fed into a software program used for social network analysis, which allowed for a final interpretation of the behaviors.

Rodrigues explains that in biological anthropology, studying primate behavior always leads to interpretation of human behavior, especially since many primate studies seek to answer questions about theories of human evolution.

In this bonobo sociogram, females (SU, AN, GI, LA, UN) are in red, males (DO, GA, BI, MA, TO) are in blue. Female–female relationships are indicated by red lines, female–male relationships are indicated by purple lines, and male–male relationships are indicated by blue lines. Line thickness indicates dyadic grooming rates.

Rodrigues, who became interested in primatology because of an animals and ethics class she took as an undergraduate student, says that the philosophical line that is drawn between humans and animals is what originally piqued her curiosity about primates.

“In philosophy, the difference between ‘human’ and ‘animal’ was based on assumed cognitive differences, including between humans and great apes,” she said. “But the more you learn ape emotion and cognition, the more blurred some of those lines become.”

So it should come as no surprise that her next project is studying humans.

“My overarching interest is in female social relationships,” Rodrigues said. “My main project (at Beckman) now is actually looking at female scientists.”

“I’m looking at both their positive and negative experiences. How social interaction—including day-to-day social support, especially female social relationships—helps deal with everyday work stressors.”

At Beckman, she is working with Kate Clancy, an associate professor of anthropology, and Liz Stine-Morrow, a professor of educational psychology—both members of the Social and Emotional Dimensions of Well-being Group.

In this article

  • Elizabeth A L Stine-Morrow
    Elizabeth A L Stine-Morrow's directory photo.
  • Kathryn Clancy
    Kathryn Clancy's directory photo.

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