When Female Gorillas Move, Friendship Matters

In the misted volcanic highlands where Rwanda’s forests crest and dip into deep valleys, mountain gorillas live in groups that are constantly in motion. Males may set off to start new groups, females may join a different troop, and the composition of these communities can change many times in a lifetime. For female gorillas, the decision to leave one group for another is rarely random. New research shows that it is shaped by something deeply social: old friends.

Female mountain gorillas seek out old friends when moving to a new group, a new study finds. Dian Fossey Gorilla Fund

A long-term study published in Proceedings of the Royal Society B¹ finds that when female gorillas decide to join a new group, they gravitate toward those containing females they’ve known in the past—sometimes after years apart.

“It’s often assumed they will not invest so much time and energy in those social relationships, because you or the other individual might disperse at any time,” says Victoire Martignac, a University of Zurich doctoral researcher. “And yet we are seeing that those relationships can matter even after years apart.”