Dispersed female networks: female gorillas’ inter-group relationships influence dispersal decisions

Dispersal is a fundamental aspect of many animal societies, impacting gene flow, knowledge transmission, culture and individual fitness. However, little is known about the information individuals use when dispersing. Mountain gorillas exhibit a flexible dispersal pattern with 50% of both sexes dispersing, and females often dispersing multiple times. Using two decades of data including 152 dispersals from 56 females, we examined how familiarity with individuals in other groups influenced dispersal. We found that females avoided groups containing males from their natal group, but preferred groups containing females they had previously resided with, particularly those from their natal group. This suggests that females prioritize the maintenance of female relationships in their dispersal decisions, while reducing inbreeding risks. Joining a new group can be costly and these pre-existing relationships may reduce dispersal costs. These findings highlight the capacity for wider-scale societies to both shape and be shaped by dispersal decisions, with long-term inter-group relationships representing potential sources of information and support in the dispersal process. This contributes to a better understanding of not only population dynamics in this endangered ape, but also of the foundation of our own flexible society, characterized by individuals moving between social groups throughout their lifetimes.