Why (and How) Groups of Animals Fight

Complex factors come into play when groups of animals decide to battle their rivals.

Three Meerkats standing
Meerkats with pups can be more motivated to fight and win to gain territory to feed their offspring. Martin Pickard / Getty Images

When two animals are about to fight, they take a number of things into consideration. They size up their rivals, based on how big they are and their perceived strength and they look at the value of the prize they’re fighting over, to make sure it’s really worth the conflict.

But when groups of animals head into battle, it’s not as simple as who has more members. Larger groups aren’t always victorious, new research finds. Many more complex factors come into play when groups of animals decide whether to fight their rivals.

Scientists from the universities of Exeter and Plymouth in the U.K. reviewed previous research on animal conflicts to study how animals make decisions about potential fights. They published their findings in Trends in Ecology and Evolution.

“They consider their own and/or their opponent’s fighting ability — usually, how big they are, but also things like the size of the weapons they sport (claws, antlers, and the like) or even things about their physiology,” lead author Patrick Green, of the Center for Ecology and Conservation on the University of Exeter's Penryn Campus, tells Treehugger.

“They also consider the value of the resource, like how much food or the age of the mate they’re fighting over.”

When group skirmishes in the animal kingdom have been researched before, the attention has typically been on the number of participants in each group.

“This has been studied in some ways before in intergroup contests — say, in wolves and many primates, among other species — but usually the focus is solely on how many individuals each group has,” Green says. “We are suggesting there is a lot of nuance that might be understudied.”

In many cases, fighting groups with the most participants are often the most victorious. Studies have shown that’s typically the case with lions, primates, ants, and birds, for example. But in other cases, there are factors that are more powerful than sheer numbers.

“It could be other aspects of ability are important (the sex of individuals in the group, say) or in how resources matter — a group fighting from its own territory might be more motivated to win the fight because it needs to hold onto this resource,” Green says. “There are also aspects of experience — groups that win prior fights might be more likely to win future fights, and losing groups to lose.”

What Matters in a Fight

When studying prior research, scientists found certain factors, other than size, that can play a part in victorious outcomes:

Motivation: Despite having smaller numbers, meerkat groups with pups can have a motivational advantage because winning new territory can mean more food for their offspring.

Changing tactics: A hermit crab fights by either rapping its shell against a rival’s or by rocking the rival’s shell back and forth. When rapping isn’t working, hermit crabs switch to rocking to increase their chances of winning.

Soldier recruitment strategies: Turtle ants will recruit ants to defend nests with narrower entrances, because those are easier to defend than larger entrances. They’ll sacrifice some nests while successfully defending parts of their territory.

Stronger members: Smaller groups of gray wolves with more males can overcome larger groups with fewer males, because males are bigger and stronger than females.

Coordination: “Groups that execute contest behaviors in a more coordinated fashion may be more likely to win,” the researchers said.

Researchers found that one of the most fascinating things about group contests is how different group members can sway the results of the competition.

“In a one-on-one fight, each individual has control over its decision-making and therefore what it does in the fight,” Green says.

“In an intergroup contest, though, there are many individuals within a group who may have different interests (say, males v. females or old v. young members). They may act in different ways, impacting how the group itself functions. We call this heterogeneity among group members, and I think it’s likely very important to intergroup contest assessment.”

View Article Sources
  1. Green, P.A. et al. "Assessment During Intergroup Contests". Trends In Ecology & Evolution, 2020. Elsevier BV, doi:10.1016/j.tree.2020.09.007.

  2. Briffa, Mark, et al. "The Role Of Skill In Animal Contests: A Neglected Component Of Fighting Ability". Pubmed Central, vol 284, no. 1863, 2020, doi:10.1098/rspb.2017.1596.