Strategic heuristics underlie animal dominance hierarchies and provide evidence of group-level social knowledge.

The question of what animals understand about their worlds is fundamental to studies of the evolution of sociality, cognition, and animal culture. However, the presence and extent of knowledge in individuals is difficult to detect, and when detections have been made, differences in methodology make cross-species comparisons difficult. We present a new method for detecting knowledge. This method infers individual-level strategic rules for aggression in dominance hierarchies where rank differences between individuals may structure decision-making. We apply this method to a data from 172 groups across 85 species in 22 orders. By looking for heuristics that depend upon knowledge of group-level facts, we can back-infer the types of knowledge individuals possess. Summary measures then place groups within a taxonomy, providing a social of group-level knowledge. This assay allows the identification of consensus strategies at the group level. The majority of animal groups in our dataset (112 groups, 65%) follow a downward heuristic, spreading aggression relatively equally across lower-ranked opponents. An additional 50 groups (29%) use strategies that are indicative of more detailed rank knowledge. Different groups within the same species can use different strategies, indicating that the choice of heuristics may be contextual and that the structuring of aggression should not be considered a fixed characteristic of a species. Instead, individuals may be able to plastically respond to changes in environmental or conditions by changing their strategies. Our approach to studying animal conflict provides new opportunities to investigate the extent of rank knowledge across species, compare the evolution of knowledge, and better understand the effect of knowledge on individual behaviour in within-group conflict.