Conflict between groups promotes later defense of a critical resource in a cooperatively breeding bird.

This is the author accepted manuscript. The final version is available on open access from Elsevier via http://dx.doi.org/10.1016/j.cub.2014.10.036Conflict between groups (intergroup conflict) is common in many social species and is widely discussed as an evolutionary driver of within-group dynamics and social structure. However, empirical studies investigating the impacts of intergroup conflict have focused on the immediate aftermath, when behavioral changes may be the direct result of elevated stress levels or territorial exclusions. Demonstrations of longer-term effects, with behavioral changes persisting once increases in stress have diminished and full access to resources is again possible, would support proposed links to individual fitness and social evolution. Here we show that conflicts between neighboring groups of cooperatively breeding green woodhoopoes (Phoeniculus purpureus) have a lasting influence on decisions concerning roost cavities, a limiting resource vital for survival and breeding. Groups involved in extended conflicts in the morning were more likely to return to the zone of conflict that evening, roosting closer to territorial borders, than when intergroup interactions were short or did not occur. Extended morning conflicts also increased the likelihood that groupmates roosted together and preened one another at the roost, suggesting that intergroup conflict promotes consensus decision-making, social bonding, and group cohesion. Border roost use and allopreening increased more following conflicts that were lost rather than won. By demonstrating that both the intensity and outcome of intergroup interactions affect resource defense and associated within-group behavior many hours later, our results begin to bridge the gap between the immediate impacts of intergroup conflict and its role in social evolution.This study complied with the laws of South Africa, where the data were collected, and was approved by the Science Faculty Animal Ethics Committee, University of Cape Town. We are grateful to Morné du Plessis for access to the study population he originally established and to Andrew Higginson, Christos Ioannou, and two anonymous referees for comments on the manuscript. The data were collected by A.N.R. while supported by a Natural Environment Research Council studentship