Animal war preparation: What animals do before going to war

Intergroup conflict is rife throughout the natural world, being found in social species from ants to primates.
Conflict over resources such as territory, space, food or mating exerts a powerful evolutionary force on social species, potentially affecting fitness and survival, say the researchers. Traditionally, research has focused on actions between rival groups during contests and the behavioural consequences afterward. But evolution can also select for pre-emptive behaviours that maximize the chances of winning in a conflict.

What is becoming very clear is that pre-emptive behaviour is widespread whenever intergroup conflict is found.
Social animals use a suite of pre-emptive behaviours in anticipation of conflict, including staying quiet, monitoring their surroundings, conducting raids and bonding through play. In a review published in Trends in Ecology & Evolution , researchers describe how environmental cues and memories of past events can trigger these behaviours. Over generations, these pre-war preparations could affect socio-cognitive evolution, population dynamics and community structures.

There is growing evidence that the amount of anticipatory behaviour displayed is dependent on the current threat level. More is seen when rivals are more likely to be encountered, larger in size, less familiar or more likely to attack.

A group of meerkats standing together in the face of an outside threat

Image source: iStock

Humans have long been known to prepare for warfare by increasing surveillance, using elevated areas to gather information, conducting ambushes and raids, and moving quietly through enemy territory to avoid detection. Recent studies of wild animals provide similar examples of preparation for encounters with rival groups.
Observations of chimpanzees have revealed that groups tend to rest on hilltops in areas where intergroup contests occur rather than engage in noisier activities such as feeding or traveling. In addition, experiments have shown that dwarf mongooses respond to olfactory or vocal cues of rivals by moving more slowly and engaging in sentinel behaviours, which allow them to monitor their surroundings more easily.

The threat of intergroup conflict can also influence animals' space-use patterns. To signal territorial ownership, dwarf mongooses deposit more scent marks in response to simulated rival intrusions, and meerkats tend to scent mark near burrows examined by intruders. Similarly, black howler monkeys return to locations of past contests, potentially to advertise their presence to neighbours.

By contrast, Japanese macaques, chacma baboons and long-tailed tits avoid areas inhabited by rivals.

Beyond space-use patterns within a commonly used area, a more extreme pre-emptive behaviour is raiding—actively seeking out rivals on their home turf. For example, male chimpanzees silently invade neighbouring territories in single file and move toward other groups' vocalizations, apparently preparing to attack rivals. Banded mongooses also engage in lethal gang attacks, conducting raids to kill the offspring of rival groups.

When the threat from outsiders is greater, various mammal species stay closer to one another. For instance, chimpanzees groom and play with one another more in advance of collective territory defense. Such behaviours likely facilitate communication, reduce anxiety, enhance bonding and promote a stronger fighting force.

There is increasing evidence that nonhuman animals adjust various behaviours to enhance information gathering, incentivize contest participation, reduce anxiety, and minimize collective and individual risk in anticipation of encounters with rival groups. These behaviours occur across a diverse range of social species.

Pre-emptive behaviour in a landscape of intergroup conflict, Trends in Ecology & Evolution (2026). DOI: 10.1016/j.tree.2026.06.002