Behaviour involved in social conflict, including threats, displays, displacements, and overt aggression.

Agonistic behaviour encompasses a range of behaviours from low-intensity displays (pinned ears, raised hackles, threatening postures) through displacement (the more dominant individual moves into the space of the less dominant, who moves away without overt conflict) to overt aggression (biting, kicking, fighting). The range of agonistic behaviours in any species is typically wider than people unfamiliar with the species realise. In horses, the displays include ear position, head height, and tail movement. In dogs, they include eye contact, body stiffness, lip retraction, and growling. In primates, threat displays involve facial expressions, vocalisations, and stylised body postures that vary substantially across primate species. Across the studied range of social mammals and birds, low-intensity displays vastly outnumber overt aggression in normally functioning groups.

Despite being more rare than affiliative behaviour in stable social groups, agonistic behaviour has historically received disproportionate research attention. A 2023 systematic review of equine social behaviour found that two-thirds of the research literature focused on agonistic interactions despite their relative rarity in actual herd life. This research bias likely exists for other social species too and probably reflects both the dramatic quality of agonistic interactions (they are more visible, more memorable, and easier to count) and historical theoretical frameworks that prioritised competition over cooperation as the central organising feature of animal social life.

The functions of agonistic behaviour include the resolution of resource conflicts (who gets access to the food, the water, the rest spot), the establishment and maintenance of social relationships (over time, repeated agonistic interactions establish patterns of who tends to win contests with whom), and protection of important assets (offspring, mates, valued resources).

Agonistic behaviour is normal and is not in itself a welfare concern, particularly when interactions are typically low-intensity and resolved quickly. The welfare concern arises when agonistic interactions are intense, frequent, prolonged, or when they cause physical injury or sustained psychological distress to one or more individuals. Groups characterised by chronic agonistic conflict typically have welfare problems and may need management intervention.

Modern welfare science has substantially complicated earlier views about agonistic behaviour and dominance. The simple linear hierarchies once thought to characterise group-living mammals have been replaced by more nuanced models that recognise context-dependence, bilateral relationships, and the relative rarity of overt aggression in stable groups.