Why Animals Swarm for Swarms Until recently, following the crowd was not seen as a desirable goal in life. These days, however, everyone is talking about swarm intelligence. But are swarms really smarter than individuals? And what rules, if any, do they follow? With the help of new computational techniques, Iain Couzin from the Max Planck Institute for Ornithology in Radolfzell imposes order on the seeming chaos of swarms. TEXT KLAUS WILHELM aboon troops are strictly hier- tested ruler again, and the other troop archical with an alpha male members must make do with his left- ruling the roost. However, overs. “Even though individuals are signs of democracy have re- self-interested, it appears that democrat- cently been observed – for ex- ic principles still apply,” says Couzin. ample,B when the animals are hunting for food. “Even the uninformed animals FROM CHILDHOOD CURIOSITY in the troop participate in decisions TO CUTTING-EDGE RESEARCHER about possible food locations and the route the troop will take to find them. As a researcher, Couzin’s heart beats This may be advantageous to the dom- faster when he tells stories like this. He inant male, as it means that he can ben- comes across like a young boy in the efit from the decisions of others when process of discovering the world, but locating good food sources,” explains the biologist has been carrying out cut- Couzin, whose department conducts re- ting-edge research for two decades and search at the University of Konstanz. regularly makes astonishing discover- However, upon reaching the food ies. His research passion: the swarm, source, the alpha male is the uncon- that most beguiling form of collective. Photo: Axel Griesch 62 MaxPlanckResearch 2 | 17 ENVIRONMENT & CLIMATE_Collective Behavior Why Animals Swarm for Swarms In nature, migrating locusts form swarms comprising over a billion individuals when too many animals live in one area. Iain Couzin wants to discover what determines the behavior of such swarms. His analyses Photo: Axel Griesch have shown that the animals are driven by the fear of being eaten. 2 | 17 MaxPlanckResearch 63 ENVIRONMENT & CLIMATE_Collective Behavior A school of fish is a self-organizing system. Decisions are based » on the movements of the individual animals “The beauty of swarms fascinated me nally have some in the laboratory imals in the Sahara some time ago, he even as a child,” says the 42-year-old again!” Couzin’s delight at this is evi- almost died of starvation. “I hallucinat- Scot. “I always wanted to know why and dent. He has had to get by without the ed,” he recalls, “and I thought I would how animals gather in large groups.” insects for a long time – too long for die.” In the end, all of the insects were Today, swarm has become a byword his taste. blown away by a sand storm, and Cou- for wisdom. Just 50 years ago, serious zin left Africa with no data. scientists fancied that telepathic forces HUNTING FOR LOCUSTS Because of this experience, he fo- were at work when, for example, thou- IN THE SAHARA cused on researching the insects in the sands of fish move and turn together as laboratory. With his team, he built a if by magic. Even when a swarm spon- Couzin has many scientific passions, circuit on which the locusts could taneously changes direction, order is but he is particularly drawn to the be- move as they pleased. Every morning maintained and there are seldom colli- havior of insects – perhaps because lo- the scientists released up to 120 ani- sions. The animals coordinate their custs have helped him reach some very mals into the perfectly secured circuit. movements considerably better than exciting research findings. By evening, however, it was found that humans driving in traffic. However, he almost paid a very high some locusts had disappeared. “This Birds and insects have similar skills. price for this: when he spent weeks went on for days and I started to doubt Consider locusts, for instance. “We fi- looking for the legendary swarming an- my own sanity, or at least my ability to count.” That was until he was able to examine video recordings of the go- ings-on in the arena in detail and made a startling discovery: the animals eat one another. After all, locusts are cannibals. Experts had considered them to be vegetarians and cooperative, for example when they suddenly form gi- ant swarms and, as one of the great Biblical plagues, strip entire swaths of land bare. “But their behavior has nothing to do with cooperation. Rather, they are driven by the fear of being cannibal- ized by others within the swarm,” ex- plains Couzin. When many insects come together, they can run out of es- sential nutrients, and that’s when they begin to turn on one another. It was Couzin (right) and his PhD student Jake Graving observe the swarm behavior of locusts in the laboratory. To this end, they built a circular track from which the animals can’t escape. Photo: Axel Griesch 64 MaxPlanckResearch 2 | 17 A school of fish is a self-organizing system. Decisions are based on the movements of the individual animals The fish cellar at the University of Konstanz is lined with aquariums like in a pet shop. The researchers keep predominantly sunbleaks and golden shiners to study what guides the behavior of fish swarms. found that each individual attempts to position, too. The individual animals in struct the animals’ fields of vision. In eat the one in front of it, and to avoid a swarm synchronize their movements this way, the scientists aim to decode being eaten by those behind. The re- in this way, even over distances of sev- the rules that govern the swarm. sult is a mobile cannibalistic horde on eral kilometers. In addition to locusts, Couzin is also a “forced march”. fascinated by another swarm-forming This discovery was considered noth- ANALYSES IN THE WILD, IN THE group of organisms: fish. For instance, ing short of groundbreaking in expert LAB AND ON THE COMPUTER he studies the golden shiner fish – a na- circles. Couzin and his colleagues found tive of North America –as juveniles, further experimental evidence support- This example illustrates Couzin’s un- with a length of around seven centime- ing his theory by severing the nerves in conventional approach to his research ters. In daylight, they swim in schools, the insects’ abdomens so that they no – holistic, if you will. He analyzes the but they remain motionless when it is longer felt the bites from behind. The animals’ behavior in the wild, in the dark. The fish follow clear rules when locusts immediately lost their ability to laboratory and in virtual realities, thus schooling: they seek out the proximity form a swarm. obtaining more comprehensive in- of conspecifics but without colliding With the aid of a computer simula- sights. To do this, he needs biologists, with them; a fish on the edge of the tion, Couzin’s team later discovered computer scientists, physicists and school is often the first to react to a that the locusts follow the laws of par- mathematicians on his team. “We have stimulus and thus disproportionately ticle physics. The animals are akin to a to teach the computer experts and bi- influences the movement of the entire “flowing magnetic field.” Their bodies ologists to speak the same language.” group. Furthermore, individual fish align with each other much like small Only by working together can they re- tend to adopt the direction selected by magnets. Changes in the position and construct animal swarms on the com- a majority. If six fish swim to the left orientation of one “particle” can cause puter. These computer models trace and five to the right, the swarm fre- Photo: Axel Griesch Photo: Axel Griesch neighboring particles to change their each individual in a swarm and recon- quently opts for the left. > 2 | 17 MaxPlanckResearch 65 Sunbleaks glide through huge basins. Cameras record their every movement. With the help of his computer models, thousands of organisms to literally But such conditions are almost impos- Couzin identified three factors that meld into a single entity. “Even com- sible to fulfill in reality. Individuals in control the behavior of a fish school: plex swarm behavior can arise from close proximity within a group tend to attraction, repulsion and alignment of simple interactions between the indi- have access to similar sensory informa- the individuals. For example, if the re- viduals. The animals don’t even have tion, so the cues they experience will searchers steer virtual individuals in to explicitly signal to one another. By not be independent, but correlated. their simulation slightly in one direc- responding to the movements of their Furthermore, individuals may use mul- tion, the group will very likely follow. neighbors, individuals can make high- tiple cues, or sensory modalities, when “So, a school of fish is a self-organizing ly effective collective decisions,” ex- making decisions. Using computer sim- system. Decisions are based on the plains Couzin. ulations of decision-making, Couzin movements of the individual animals,” and his colleague Albert Kao were able explains Couzin. If individual animals SMALLER GROUPS MAY MAKE to demonstrate that the conventional change direction, or suddenly swim BETTER DECISIONS view of the wisdom of crowds does not more slowly, their neighbors usually re- hold up when this realism is added. In act. The sum of the position and direc- However, as one of Couzin’s most re- most cases, they found that small to tion changes ultimately determines cent studies suggests, the wisdom of a medium-sized groups with between where the school will swim.