Adaptive social ties drive post-fission group choice in blue monkeys

Permanent group fissions present rare opportunities for individuals in philopatric groups to select their groupmates, and so by studying post-fission group choice, we can gain insight into how sociality influences decision-making. Our first analysis investigated which social ties influence post-fission group choice in blue monkeys by considering a female’s ties to kin, non-kin, the original group’s resident male, her risk of infanticide, and her position in the dominance hierarchy in each potential post-fission group. We used nine conditional logit models to analyze how females make this choice, employing alternative ways to quantify social ties to groupmates. We conducted a post-hoc analysis to further investigate which factors influence maternally-related kin to split into different post-fission groups. This study used two datasets, one for the group choice analysis and one for the post-hoc analysis. We also present the R code for the analyses we report in the associated manuscript., Observational data were collected from blue monkeys (Cercopithecus mitis stuhlmanni) in the Kakamega Forest, western Kenya surrounding five instances of group fission that occurred between 2008 and 2019. During the study period, trained observers monitored the different groups on a near daily basis, conducting focal animal samples on all adult females (classified as adults the day they give birth to their first offspring). Focal animal samples were designed to last 30 min, and were retained in the dataset if they were at least 20 min long. Females were chosen as subjects to accumulate focal samples evenly among different periods of the day (morning, midday, afternoon) and over time. Instantaneous recording of the focal subject’s behavior occurred every minute and included the identities of any social partners and individuals in proximity (within 1m). Agonistic interactions (with one individual showing submission) were recorded during focal samples and ad libitum.
We included females as ..., , # Adaptive social ties drive post-fission group choice in blue monkeys

[https://doi.org/10.5061/dryad.xd2547drj](https://doi.org/10.5061/dryad.xd2547drj)

Permanent group fissions present rare opportunities for individuals in philopatric groups to select their groupmates, and so by studying post-fission group choice, we can gain insight into how sociality influences decision-making. Our study investigated which social ties influence post-fission group choice in blue monkeys by considering a female’s ties to kin, non-kin, the original group’s resident male, her risk of infanticide, and her position in the dominance hierarchy in each potential post-fission group. We found that females maintained several different kinds of relationships during fission (those with kin, non-kin, and the original group’s resident male), making trade-offs between ties only when there was a more immediate threat to their fitness (potential infanticide). Here we present two datasets used in this analysis, one r...