Swarms, schools and skeins: the who, what and why of collective animal behaviour

Beverly McClenaghan
17 October 2017

Above: Image © subaquapix, istockphoto.com

Have you ever accidentally walked into a swarm of flies? Watched a school of fish darting through the water? Seen a skein of geese fly overhead as they migrated south?

Swarm, school and skein all refer to groups of animals moving together. Have you ever seen a group like this and wondered how they managed to turn and change shape at the same time? Did you wonder why they travelled together rather than on their own?

Scientists are just starting to understand the mysterious behaviour of these animal groups. And what they’ve understood so far is that travelling together helps these animals stay safe and save energy.

What is collective animal behaviour?

Scientists use the term collective animal behaviour to describe the coordinated movement of a group of animals of the same species.

Jellyfish at the Montery Bay Aquarium
Source: Carol M. Highsmith, Wikimedia Commons

These animal groups come in various sizes. Some groups have a few members. Others have over a million!

Their movements vary, too. Some travel in loose formations. Others travel using highly coordinated movement. Either way, collective animal behaviour in action is a pretty amazing thing to watch!

Which animals stick together?

Animals from almost every phylum participate in collective behavior. You can probably think of quite a few animals that do it, like starlings, goldfish, antelopes, and cockroaches. But some animals you might not have thought of gather in groups as well - like spiders and jellyfish, for example.

Many species participate in collective behaviour throughout their lives. Others do it only as juveniles or only as adults.

Did you know? The biggest recorded swarm of locusts occurred in 1875 in the United States. People estimated that this swarm consisted of trillions of insects!

Why do they do it?

Sticking together has many benefits for individual animals. For example, it protects them from predators.

Predators have a harder time capturing individual animals travelling in groups. After all, groups have more eyes on the lookout. They often detect predators earlier than individual animals can, which gives the group of prey more time to avoid them.

Groups can sometimes find food faster than individuals. This, again, is because there are more eyes on the job.

It’s not just about their eyes, either. Individuals who travel in groups can save energy during locomotion (movement). Some fish in schools and birds flying in formation take advantage of water or air patterns generated by individuals around them. This lets them use their energy as efficiently as possible.

Geese flying in V formation
Source: Martyn Gorman, Wikimedia Commons

For instance, have you ever seen migrating birds flying in their famous “V” formation? These birds time their wingbeats to catch the updraft (upward moving wind) generated by the bird in front of them. Catching these updrafts means the birds need to use less energy.

How do they do it?

Different species coordinate their movements in different ways. You might watch groups doing some complicated moves and think, “They must be following a leader.”

But sometimes, group behaviour comes from self-organization. In other words, instead of copying a leader, individual animals might respond to those around them. This is kind of like how, if you were in an audience and everyone around you started clapping, you’d clap, too.

For example, research shows that large groups of starlings respond to the movement of their seven nearest neighbors.

Did you know? The principles of collective animal behaviour apply to humans, too! In crowds, people respond to the movement of people closest to them. This happens the same way birds in flocks respond to the movement of birds closest to them.

Self-organization can also happen when animals respond to nearby stimuli. For example, ants moving in a collective trail respond to the chemical cues left by other ants. Here’s how this might work: An ant leaves a pheromone trail to a food source. Other ants follow this trail to the food source and add their own pheromones to the trail. More and more ants follow the trail and add more pheromones to it, which it turn attracts even more ants.

Each individual responds to changes in direction and speed from the animals surrounding it. In this way, a signal can pass through a group of animals very quickly. The whole group can respond to a stimulus without a single leader. That’s pretty amazing - especially when you consider that a group can have over a million individuals!  

Which animals don’t stick together?

Clearly, participating in collective behaviour has some major advantages. So why don’t all animals do it? It’s likely because animals that don’t do it have evolved other ways of staying safe and saving energy.

For instance, turtles don’t move in groups. But their hard shells do a pretty good job of protecting them from predators!

Collective behaviour beyond the animal world

Researchers are developing new tools for studying collective animal behaviour. They’re also applying these tools to other fields, some of which involve humans. They’re even applying them in sports!

For example, you’ve already learned that some animals stay in formation to stay safe against predators. Those that stay in formation survive, and those that don’t stay in formation might get eaten or simply left behind. It’s the survival of the fittest, and animals in formation are fitter. That’s why animals continue to use the strategy of staying together.

A similar principle applies in soccer, where certain player formations are more successful than others. The formations of winning teams last because other teams start to use them. Meanwhile, unsuccessful teams will stop using their formations, and will try new tactics instead.

Researchers are using mathematics to track the positions and movements of soccer players. In other words, they’re using concepts from the animal world to understand how human teams develop winning strategy!

Learn more!

We Just Learned How 'Crazy Ants' Ever Get Anything Done (2015)
M. Wei-Haas, National Geographic

Migrating Birds Use Precise Flight Formations to Maximize Energy Efficiency (2014)
C. Ward, Scientific American

The principles of collective animal behaviour (2006)
D.J.T. Sumpter, Philos Trans R Soc Lond B Biol Sci. 361

Beverly McClenaghan

I have always loved animals and nature. This led me to pursue an undergraduate degree in zoology at the University of Guelph followed by a Master’s degree at Trent University studying avian ecology and conservation. Currently, I am working for a conservation organization in St John’s, Newfoundland. I am working in policy and outreach, which is teaching me a lot about the economic, cultural, and social side of conservation as well as the biology of conservation. Outside of work, I am an avid birdwatcher, rock climber, and hiker. I love sharing my passion for nature with others!







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