Battles between rival groups are a story as old as time. This sounds like a human story, but it is also one that is playing out across nature.
Author
- Josh Arbon
Postdoctoral Research Fellow in Zoology, University of Cambridge
Conflict between groups of animals competing for territory and resources is widespread, and contests between animals can be dangerous. Getting ambushed, especially by a larger or more powerful group, can have disastrous consequences.
However, conflict is sometimes unavoidable.
Emerging research shows war preparations are not a trait unique to humans.
A new article by my colleagues and I highlights how many of the same principles apply to animals too, and not just in our closest relatives like apes. We reviewed the literature and found examples throughout the animal kingdom of animals preparing for future conflicts . This behaviour probably explains how animals persist in the face of often intense conflict.
Animals may sense the recent presence of their rivals. Many species, such as dwarf mongooses, leave scent marks to advertise their presence, and react to those laid down by rival groups. Others animals may rely on their memories of past conflict to change their behaviour in situations they deem risky, such as at territory edges or contested resources.
There can be sex differences in how animals approach conflict. Vervet monkeys are a good example here. Males often stand to lose more from conflict, while females stand to benefit – as it could lead to securing long-term access to high-quality food. Researchers have observed males attempting to defuse conflict yet females try to promote male participation .
When assessing that the risk of conflict, there are many questions for animals to consider. Are rival groups likely to be close by? How powerful are they ? Are they restricting access to key resources? Do you have vulnerable offspring to protect?
Animals use many different approaches to reduce the dangers rivals may pose. Here are three main ones:
1. Inform yourself
Information is power. Across group-living species, from mongooses to invertebrates, there is evidence that animals can prioritise gathering information in risky situations. Chimpanzees have been seen to climb to the top of hills and wait quietly, listening out for rivals before making their next move.
Similarly, when groups of dwarf mongooses encounter the scent of rivals, they move less, investigate their surroundings more and post more sentinels to look out for danger. Gathering information comes at a cost, often in the form of lost opportunities to find food and engage in social interactions. But if the risk is high this can be a small price to pay.
2. Strategise
The way animals use space can be crucial. Some species, such as long-tailed tits and chacma baboons, choose to minimise the time they spend in risky areas, such as where territory overlaps. Others animals, such as meerkats, lay down scent marks near their burrows, which are a valuable resource.
Staying within familiar areas and defending them can give groups of animals a home advantage, as groups are more likely to win when they are on familiar ground. Groups can also stay closer to one another, reducing the chances of animals getting isolated should a contest arise suddenly.
Many species, including ants and apes, raid rival groups. These include targeted forays into rival territory with the goal of injuring and even killing rivals to reduce the threat they pose to their own group. Raids in ant species also allow groups to steal the brood of their rivals, bolstering their future fighting force.
3. Stick together
Make sure your groupmates have your back. Although groups often cooperate with one another, animals can be out for themselves, especially those less related to their groupmates or with less to gain from winning.
Group members therefore need to be confident that the others won’t turn tail when the going gets tough. This can be achieved by both carrot and stick. Chimpanzees play and groom more before conflict occurs . These bond-building activities aim to ensure nobody defects if backs are against the wall. It happens more on days when they later engage in conflict, which suggests they know to some degree that an attack will be more likely.
Vervet monkeys, however, take a different approach. Monkeys that failed to participate in previous contests can face aggression from groupmates , coercing them to step up and help next time.
All of this preemptive behaviour can require animals to keep track of who their rivals are, how strong they are and where they might be. Gathering and processing this information can take a lot of effort. But if it allows animal groups to survive, then intergroup conflict may lead to the evolution of cognitive abilities . Indeed, researchers have suggested the need to outmanoeuvre rivals contributed to the intelligence we have as humans today. That is not to say that all anticipation is mentally costly. When rivals are predictable, simple rules can suffice.
Although our work focused on animals in groups, many of the same principles should generalise to solitary and pair-living animals too. Just imagine how many potential cold wars are playing out between rival animals, each trying to preempt the other while going about their daily lives.
