Activity synchronization and fission decisions

Group-living animals need to reach a consensus to maintain cohesion. When the costs of consensus outweigh the benefits, the group may (temporarily) split into two or more subgroups. Consensus can concern the activity to pursue or the direction of travel. Temporary group separation is a common feature in species with a high degree of fission-fusion dynamics. We investigated the role activity synchronization played in fission decisions in a spider monkey group living in the Otoch Ma'ax Yetel Kooh Nature Reserve, Yucatan, Mexico. For 21 months, we recorded every fission event occurring in the followed subgroup, as well as the subgroup activity. We classified the activity as "synchronized" when at least the 75% of subgroup members performed the same activity (resting, foraging, socializing or traveling); otherwise, we classified it as "non-synchronized". We found that fission events occurred more often when the activity was non-synchronized. In addition, when the activity was synchronized, fission events occurred more often when spider monkeys were traveling than when they engaged in other subgroup activities. Our findings highlight the role of consensus over the activity to pursue and the direction where to travel on fission decisions.