Female Gorillas Form Ties That Bind, Helping Them Join New Social Groups
A new study finds that when female mountain gorillas move to a new crowd, they look for females they’ve already met
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What do you do when you first walk into a party? Maybe you scan the room looking for friends. If you don’t see any, or if you see someone you’d rather avoid, you might just sneak out and head to another gathering. Now, a new study of female mountain gorillas in Rwanda suggests they do the same thing.
According to the paper, published Wednesday in Proceedings of the Royal Society B, female gorillas joining new social groups gravitate toward other females they have known in the past.
“Going into a new group could feel pretty scary, with individuals usually entering at the bottom of the social hierarchy,” Robin Morrison, a behavioral ecologist at the University of Zurich and senior author of the new study, says in a statement. “A familiar female might help reduce this, providing a social ally.”
Need to know: Is the mountain gorilla endangered?
The mountain gorilla is an endangered subspecies of the eastern gorilla, with 1,063 individuals counted in 2024. However, their numbers are increasing.
Researchers have long studied the social dynamics of great apes, and they’ve found that relationships among gorillas have complex impacts on their health. The new study focuses on dispersal, a common occurrence where gorillas leave one social group and join another. When male gorillas disperse, they often become solitary and try to establish a new group. But when females disperse, they have to find an existing group to take them in.
Dispersal is important for wild gorillas, as lead author Victoire Martignac, an evolutionary anthropologist at the University of Zurich, tells BBC News’ Victoria Gill. After all, it helps avoid inbreeding and promotes genetic diversity. “But it’s extremely hard to study,” Martignac says, “because once individuals leave a group, it’s hard to keep track of them.”
Martignac and her colleagues overcame that challenge by looking at more than 20 years of data collected with continuous monitoring by the Dian Fossey Gorilla Fund. This allowed the researchers to track 56 females as they moved between groups and to search for patterns in where the gorillas chose to go and why.
The team found that female gorillas joined groups containing other females they’d known for at least five years or had seen in the past two years. That finding upends an assumption among scientists that it’s not worthwhile for females to invest in same-sex relationships, since individuals might leave the group at any time. The gorillas also tended to avoid males they knew growing up, likely because they might be related.
“This really tells us that it’s not just who they know that matters but how they know them,” Martignac says in the statement. Other factors, such as the size or sex ratio of the group, didn’t seem to affect a female gorilla’s choice to join.
Robert Seyfarth, a psychologist at the University of Pennsylvania who wasn’t involved in the study, tells NPR’s Nell Greenfieldboyce that this type of long-term work tracking multiple groups is valuable to scientists studying animal behavior, and it opens up new questions for further research about the reasons behind gorillas’ social choices. “Does this preference make a difference in terms of survival and reproduction?”
The work could also teach us about ourselves and our past, since, as humans, we also move between social groups. “Movement is a huge part of the way we live,” Martignac tells BBC News. “But those decisions do not fossilize. … So, we look at them in our closest evolutionary cousins.”