Adaptive benefits of group fission: evidence from blue monkeys

Permanent group fissions are thought to represent the tipping point at which a group has become too large and therefore splits into two, allowing for an evaluation of the consequences of living in too large a group and if fission can alleviate those costs. We first examined how adult female activity budgets (feeding, moving, resting) differed among periods surrounding (i.e., before and after) multiple fission events, accounting for seasonal variation, and using five mixed-effects beta regression models. We then assessed how rates of agonism differed among periods surrounding these fission events using two negative binomial models, one examining all agonistic interactions and one focusing on agonistic interactions that were lost. Our third analysis used a generalized linear mixed model to investigate a female’s likelihood of conception in a given month, based on her individual characteristics, which post-fission group size she joined, and whether that month fell before vs. after fission,..., The datasets relate to seven fission events that occurred between 1999 and 2019 in the blue monkey population inhabiting the Kakamega Forest, western Kenya. We used data from all seven fissions for records of female conceptions and infant survival and data from the last five fissions only (2008 to 2019) for records of female behavior, because only these last five fissions occurred while the long-term monitoring protocol included focal animal follows of adult females, which allowed systematic recording of activity.
Throughout the study period, a team of trained observers monitored the study groups for all or part of a day on a near daily basis. All group members could be identified as individuals. Observers documented which individuals were present and whether any sub-grouping occurred, meaning that group members were separated into two parties that traveled and foraged separately for at least part of the day. They also recorded all observed agonistic interactions, noting winners and los..., , # Data from: Adaptive benefits of group fission: evidence from blue monkeys

[https://doi.org/10.5061/dryad.0cfxpnwbb](https://doi.org/10.5061/dryad.0cfxpnwbb)

## Description of the data and file structure

Permanent group fissions represent the tipping point where a group has become too large and thus splits into two, allowing for an evaluation of the consequences of living in too large a group and if fission can alleviate those costs. Our study investigated how female activity budgets, rates of agonism, likelihood of conception, and offspring survival changed before vs. after group fission. Accounting for seasonal variation, we found that females spent less time feeding in general and on preferred food items right before fission than during any other period. We also found that females were less likely to conceive in the two years leading up to fission, and that offspring survival was reduced for infants born up to two years before fission compared to those born after or during stable...,