What Animals Do Before Going to War

Intergroup conflict is common across the animal kingdom, shaping how social species survive and reproduce. A new review in Trends in Ecology & Evolution argues that many animals do not simply respond after a fight begins. Instead, they run a hidden “pre-war” program—behavioral routines triggered by environmental cues and memory of prior encounters.

The authors focus on a suite of preemptive behaviors, including quieting activity, surveying surroundings, initiating raids, and strengthening group cohesion through play. These actions can increase the odds of success by improving information collection, reducing uncertainty, and coordinating collective responses before direct contact occurs.

According to the review, the intensity of anticipation is not random. Threat level appears to modulate behavior: animals show more preparatory actions when rivals are more likely to be encountered, larger in size, less familiar, or more prone to attack. This suggests an adaptive decision process that balances the costs of readiness against the benefits of gaining an advantage.

Evidence from multiple species supports the idea. In chimpanzees, groups may preferentially rest on hilltops where intergroup contests occur rather than engage in noisier activities like feeding or traveling. Dwarf mongooses slow down and switch to sentinel behaviors after detecting olfactory or vocal cues from rivals, effectively improving vigilance while maintaining readiness.

Space use also changes when conflict is likely. Dwarf mongooses increase scent marking after simulated intrusions, and meerkats tend to mark near burrows investigated by intruders. Other primates and birds show contrast patterns—some avoid areas occupied by rival groups, while others return to sites linked to past confrontations, potentially to advertise presence or deter competitors.

A stronger escalation can involve raids: chimpanzees may silently move toward rival-group vocalizations, apparently staging for attack, while banded mongooses conduct lethal group offensives that target offspring of competing groups. Such tactics highlight how anticipation can extend beyond surveillance into proactive aggression.

When outsiders pose a higher risk, mammals can cluster more tightly. Chimpanzees groom and play with one another before collective territory defense, behaviors that likely enhance communication, reduce anxiety, and create a more effective fighting unit.

The review concludes that preemptive behavior may be a major driver of socio-cognitive evolution, because animals must evaluate cues, update expectations using memory, and adjust group coordination accordingly. Future work, the authors note, must separate what animals learn from what they sense in the moment—linking signals, cues, and historical experience.

In doing so, studying the full timeline of conflict—from anticipation to aftermath—could illuminate not only how animals manage risk but also the deep evolutionary roots of social conflict strategies, including those in humans.