Wheeling, turning, and diving—flocks of birds and schools of fish perform these acrobatic maneuvers with the precision of fighter jets in formation. Hundreds, sometimes thousands, of individuals coordinate their movements in a whirl of motion. Some collectives are so cohesive, people used to think group members employed telepathy to communicate changes of shape or direction.
But as Princeton University biologist Iain Couzin has discovered, the mysterious motivations of animals engaged in collective behaviors are anything but supernatural.
Couzin has found that only a small percentage of a group of animals, like fish or humans, can dictate the movements of the entire group. Couzin’s human studies showed that the placement of "informed leaders"—people who know where they’re going—near the center and periphery of groups increased the speed and accuracy with which the group moved towards a target. His latest work, on the role of uninformed followers, will soon be in press.
Couzin also has shown that different species form groups using similar principles. Perhaps best known for his work on locust swarms, Couzin uses innovative approaches to study collective animal motion—earning him the 2008 Searle Scholar award for outstanding research by a young investigator. Popular Science included him in its annual Brilliant 10 list for 2010.
At the February 2011 American Association for the Advancement of Science meeting in Washington, D.C., Couzin broke from a herd of journalists and researchers to speak with SciCom’s Jane Lee about collective animal motion—and how video games help him do his job.
How do animals that are usually solitary, such as locusts, come together in huge groups?
When locust populations become dense and resources become scarce, the locusts come together to fight it out over limited resources. They seem mostly to be limited by protein, salt, and water. Yet, they themselves are perfectly packaged sources of those exact nutrients.
Really they’re making the best of a bad job. If they leave the swarm, they’re almost doomed to death because there are no other nutrients out there, or they’re very unlikely to find them. If they stay in the swarm, they risk being cannibalized. But, they also can gain the benefits of cannibalizing others.
These swarms also spontaneously start moving in a straight line. By being in a swarm, this creates a very directed motion and allows them to escape nutrient-poor areas.
How does that happen? How do they all start walking in a straight line?
They all start trying to eat each other and trying to avoid being eaten. The optimal strategy, if others are trying to eat you, is to move away from those moving toward you, and move toward those moving away from you. Effectively, you’re aligning with others. Each individual, by aligning with local neighbors, and by them aligning with their local neighbors, and so on, means the whole swarm becomes very, very directed. It can move more or less in the same direction for many days.
"We’re setting up a website called Open Swarm to educate the public about collective behavior—and to see whether we can use a swarm approach to studying swarms."
I played your locust video game.
Loopy Locusts! That’s written by a guy named Ryan Chisholm, who was a graduate student at Princeton. He didn’t tell us about it, he just wrote it. He told me about it in a pub, I played it, and then we put a link to it on our website. I thought that was hilarious.
How do animal groups fall apart?
If you’re a locust that suddenly gets this rich food source, that’s going to sate you, which is going to reduce your cannibalistic tendency. That’s going to reduce your biting of others and your running away from others, which reduces the collective motion, which causes the swarm to spontaneously dissipate.
Is that the case with lemmings? There’s this popular myth that they all commit suicide or leap off cliffs. I’ve heard they start these movements because of scarce resources.
That’s a myth, of course, that they throw themselves off cliffs. Wikipedia has a very nice story about the lemmings. I think it all comes from a Disney movie where they were sort of throwing lemmings off a cliff. But it’s not necessarily a myth that they have mass migrations.
Do you see any difference between marine organisms and terrestrial organisms because marine organisms have to deal with currents?
It’s really important to think about the feedback between the physical environment and the social environment of animals. With animals like krill, they are partly structuring themselves, but they’re partly structured by the environment. That structure can be quite complex and can be very important in terms of the behavior of the predators who hunt those animals. Similarly, with cliff swallows feeding on swarming insects—those insects are pulled and pushed by wind. Again, we think it’s important to consider the unpredictability and the complexity of that type of food source. We think that’s been very important in the evolution of the behavior of these predators.
What are the underlying principles of animal aggregation?
Well, we’re still trying to reveal the underlying principles. There are certain key principles, such as local attractions, that really matter. You can get large-scale behavior emerging from local interactions. There are other principles regarding how information transfers within a group that really is independent of the exact system. We could be talking about cell groups, we could be talking about human groups, we could be talking about fish schools, and yet the principles still hold of how information transfers within groups and how groups can come to consensus decisions.
I was curious about how these principles apply to cells.
If you think about a developing embryo, it’s all about collective migration. There’s no blueprint or template, although sometimes there are chemical gradients. One nice example is the formation of the lateral line [which helps detect vibrations in the water] in fish. There’s a group of leader cells that actually migrate, and if you take them out, everything stops migrating. Put them back in and everything starts migrating again.
We’re beginning to think this type of principle is very important for development.
Do you consider yourself a biologist or a computer modeler?
I’m a biologist, absolutely. But biology is a very quantitative subject, and it’s very important to use technological advances like computer tracking. We use a lot of techniques from the video game industry. By utilizing this type of technology we can really learn new things about how the world works.
We’re just starting a project using the Microsoft Kinect, the 3D motion controller for the Xbox. We’re planning to use that to track humans and animals in three dimensions to look at collective behavior. It’s something I think biologists shouldn’t shy away from, learning some mathematics and computational tools to improve their science.
When you come up with these computer models, do you go out and observe animals making decisions and then input those observations?
I’ve only recently had a lab where I can work with real animals. Some of my earlier work was using computer models to try to understand the principles. But now what we can do is much more sophisticated. We can actually look at the real animals and try and do controlled experiments.
What kinds of animals do you have in the lab?
At Princeton, the only animals we currently have are fish. We’re going to get ants soon. We’re also working on humans, but we don’t have them in the lab other than the researchers. We do often use ourselves in trial experiments, like testing the Kinect.
I noticed you do a lot of outreach. Do you have any plans to expand on that?
My mum’s a teacher, two of my brothers are teachers, and it’s just a pleasure to present work to a general audience. We’re trying to set up a website called Open Swarm to educate the public about collective behavior, as well as to share our resources. I get contacted by people from all around the world saying, "I don’t have any formal training in computer science, but I’ve been developing this simulation of ants," or "I’m a retired engineer, but I’m very interested in swarming." There just seems to be this huge community of people fascinated by this phenomenon.
So the idea of Open Swarm is to build this community, outline the key remaining questions, and see whether we can use a swarm approach to studying swarms.
We’re also trying to improve our writing abilities to make our scientific papers less opaque. We’re trying to use less jargon. Many of those words don’t actually improve the quality of the science. They just make it harder to understand. We’re getting funded by the public to do this research. We should be able to make our work as accessible as possible.
Do you get any push-back from your colleagues about the amount of outreach you do?
No, I don’t. I certainly don’t. I only get support. I think if I just spent my entire time doing popular science stuff and didn’t have a research program, then the chair of my department would probably have a chat with me. It’s a difficult balance because of the finite time problem. But it’s a balance worth keeping. I think it’s very dangerous just to get stuck in your lab and not be aware of what’s going on, either in the outside scientific community or in the world at large.
Jane Lee, a 2011 graduate of the Science Communication Program at UC Santa Cruz, earned her bachelor's degree in integrative biology and English from UC Berkeley and her master's degree in marine biology from UCLA. She worked as a reporting intern at the Monterey County Herald, the Monterey Bay Aquarium Research Institute's news office, Wired.com, the San Jose Mercury News (Kaiser Family Foundation health reporting internship), and the San Francisco Exploratorium. She is now on a 6-month internship at Science in Washington, D.C.
© 2011 Jane Lee