How social animals quietly prepare for conflict

Well before two animal groups come face to face in a fight, many have already begun preparing for war. A new review finds that social animals throughout the natural world quietly get ready for conflict by scouting rivals, occupying high ground, strengthening alliances and, sometimes, entering enemy territory to strike first.

These preparations form a largely hidden opening chapter of animal conflict, which scientists have tended to overlook in favour of the fighting itself. A closer look could improve researchers’ understanding of animal societies and provide fresh clues about the deep origins of human warfare.

The overlooked buildup to animal conflict

The argument comes from a review published in Trends in Ecology & Evolution, bringing together decades of field studies involving insects, birds and mammals.

Despite the differences between these animals, a common pattern emerges: groups change their behaviour before any rival comes into view.

Josh Arbon, a behavioural ecologist at the University of Bristol, wrote the review with his colleague Andrew Radford, a professor of behavioural ecology at the same university. They describe this early stage as pre-emptive behaviour: anything a group does in anticipation of a clash, rather than during or after it.

For many years, research into animal conflict focused on the contests and their aftermath, giving little attention to the buildup. Yet evolution can also favour animals that put themselves in a winning position before the first blow is struck.

Preparing for rivals

The extent of the preparations depends on how threatening neighbouring groups appear. Animals prepare more when rivals are more likely to be encountered, more numerous, unfamiliar or more prone to attack.

The researchers were particularly struck by how routine this vigilance is, even in places where fights rarely occur.

Asked by Earth.com which findings stood out, Arbon, the review’s first author, said, “This goes to show that just because something is unlikely to happen it doesn’t diminish its importance, nor the need to prepare for it.”

Taking the high ground

When humans prepare for war, they often increase surveillance, occupy high ground for a better view, set ambushes and move quietly through hostile territory to avoid detection. Other animals use many of the same tactics.

Chimpanzees behave in a remarkably similar way. Where groups come into conflict, they assemble on hilltops and become quiet, resting instead of feeding or travelling in ways that could reveal their presence. One study of wild chimpanzees found that they climb to high, open ground much more frequently in areas where encounters with rivals are likely.

Dwarf mongooses are small carnivores that live in close-knit groups and defend a territory together. When they detect a rival’s scent or calls, they slow down and post lookouts. Guards on raised positions can survey the area and warn the rest of the group, while the quieter, more vigilant behaviour gives the animals time to learn who is nearby.

Information is the common thread. Before committing to a fight they cannot easily win, these animals gather what they can about their rivals’ strength and whereabouts, while trying not to reveal their own presence.

Marking territory and raiding

Anticipation also alters the way animals move around their territory. Following a simulated intrusion by rivals, dwarf mongooses leave additional scent marks, while meerkats add their own marks near burrows inspected by intruders. Both behaviours appear to reassert ownership of the area.

Some species revisit the locations of previous clashes. Black howler monkeys, for example, return to places where contests have occurred, apparently to remind neighbouring groups that they are still present.

Others take the opposite approach and avoid areas used by rivals. The habit has been observed in some monkeys, baboons and small songbirds.

Planning a raid

The boldest form of preparation is raiding: deliberately entering a rival’s territory to seek them out. Male chimpanzees move silently and in single file into neighbouring territory, then approach the other group’s calls, apparently preparing an attack.

That silence is part of what makes the behaviour seem familiar. In an email to Earth.com, Arbon said, “The way raiding chimpanzees move silently through their rivals territory is strikingly human and reminds me of childhood games of capture the flag, although the consequences of chimp conflict can be much more severe!”

Recent observations of one wild community recorded this kind of lethal raiding after the group split in two. The killing started only after the two sides had drifted apart and become separate groups.

Banded mongooses go further, carrying out deadly group raids and sometimes killing the pups of rival groups. Although the details vary between species, the same underlying logic appears across a strikingly broad range of social animals.

Closing the ranks

Preparing for conflict involves more than tactics and territory. With outsiders looming, many mammals move closer together, both physically and socially, before defending their territory as a group.

Chimpanzees spend more time grooming and playing with one another ahead of collective defence. Some have been observed drumming on tree roots to summon groupmates, while banded mongooses and meerkats use calls to recruit others after detecting a rival’s fresh scent.

That increased closeness probably serves a practical purpose. Grooming and play strengthen bonds between individuals, making an animal quicker to support a groupmate it feels connected to and helping prevent the group from falling apart when a fight goes against it. Arbon told Earth.com, “You could think of it as a team-building activity.”

Conflict and cognition

Despite the growing number of examples, major questions remain about what is happening in the animals’ minds. It is still uncertain how a group assesses the threat it faces and how much mental effort the process requires.

Some responses appear to be linked to immediate cues, such as a rival’s scent or call, while others may draw on memories of previous encounters. Separating the two is difficult. Radford believes the implications for animals could be profound. “Intergroup conflict could be an important social driver of cognitive evolution,” said Radford, the review’s senior author.

There are already signs of how finely tuned these responses can be. In a study that followed wild dwarf mongooses over ten years, groups changed where they went and how loudly they called according to the size of the rival they might encounter. Smaller groups effectively held their own against larger ones by assessing the danger and moving around it.

The review makes clear that conflict between animal groups does not begin when the two sides meet. It starts much earlier, during an extended period of scouting and quiet preparation that scientists are only beginning to map.

Examining that fuller timeline could help researchers interpret animal societies more accurately and illuminate the origins of our own habit of preparing for war. “To understand fully the influence and importance of intergroup conflict, including for our own evolution, we must study the complete timeline of behaviors,” said Arbon.