Image: Brants in wildlife refuge
U.S. Fish and Wildlife Service
Brants fly as a flock above the Arctic National Wildlife Refuge in Alaska. Scientists say such flocks tend to follow a few individuals in the know.
updated 2/8/2005 1:25:17 PM ET 2005-02-08T18:25:17

Bees do it. Birds do it. So do fish and wildebeests. They are all able to gracefully flock or swarm in a particular direction even though not every member of the group knows where they are going.

Even human beings will tend to follow each other with a herd mentality — say, out of a crowded theater. New research provides some surprising insight into what's going on, including a group penchant for democratic decisions.

"Groups of animals move purposefully, yet often only relatively few individuals have pertinent information as to where to travel," said Iain Couzin of the University of Oxford.

Biologists have often wondered if there is some complex communication that goes on between the informed and the uninformed. But Couzin and his collaborators have shown in simulations that a simple set of behavioral rules can control a group.

"There’s no explicit signaling in our model," Couzin told LiveScience. "No one is saying, ‘I know something – come follow me.’"

The only requirement seems to be a balance between a need to stay in the group and a desire on the part of some to go off in their own preferred direction. These goal-oriented individuals look just like their naïve colleagues.

"No inherent differences — genetic or otherwise, such as dominance or body size — need to be invoked to explain leadership," Couzin said.

The fact that the followers in the simulation have no way to recognize who is leading them may explain how animals efficiently move in crowded environments, where they can only see their nearest neighbors.

"[This study] demonstrates the power of the little guy," said Daniel Rubenstein of Princeton University, who did not participate in the study. "You don't need avowed leaders, you don't need complex signaling."

The results, published in the Feb. 3 issue of the journal Nature, might be useful in developing swarms of robots for exploring the oceans or other planets.

Follow the virtual leader
In computer simulations, Couzin and his colleagues programmed virtual animals with the instinct to stay near others — an important survival trait in many species. The researchers then endowed some members in the flock with a preferred direction — be it toward a food source or a new nesting site.

They then determined how close the group would come to arriving at this goal.

Accuracy increased as more of the members knew where to go. But at a certain point, adding more informed individuals did not increase the accuracy by very much. To give an example, a group of 10 gets about the same advantage from having five leaders as having six.

The minimum percentage of informed individuals needed to achieve a certain level of accuracy depended on the size of the group. If 10 virtual buffaloes need 50 percent of the herd to know where the watering hole is, a group of 200 can get by with only 5 percent.

In nature, it is likely that the number of leaders is kept as low as possible. Couzin gave the example of bees, for which scouting out a new nest site is dangerous, as well as time-consuming. Studies have shown that only 5 percent of a hive’s population gets involved with scouting.

Nature follows democratic principles
As is the case in human interactions, there will sometimes be a disagreement between those who are in the know.

For instance, there may be five individuals who know of a food supply to the east, but four others who have spotted food to the north. The researchers found that the entire group will tend to settle on the direction with the greater number of informed individuals.

"In the real world, you do have individuals with different information, needs and preferences," Couzin explained. "What we show is that — using very simple rules — the group will choose the majority. It’s almost like a democratic decision."

To test whether these simple rules actually apply in real animals, Couzin’s team has begun experiments in which certain fish are trained to associate one direction with a reward. These informed individuals will then be mixed with untrained fish to see if the group can be led.

Informed humans and robots
The scientists also plan to look at human crowds. Couzin thinks there may be a similar sort of mechanism to explain, say, how we walk along a busy street.

"We do it more or less on autopilot," he said.

Perhaps we are subconsciously reconciling two simple commands: get to work on time and avoid stepping on anyone’s shoes.

"The mechanism of coordination we propose is very simple and requires only limited cognitive ability," Couzin said. "This simplicity, generality and the effectiveness of the mechanism lend support to its being selected for in populations."

The simple network of commands may also be an efficient way to program teams of robots. Couzin has previously worked with researchers at Princeton who are designing underwater robots that can act autonomously.

Robots that learn the location of a certain target could lead other robots to it without any human supervision.

© 2012 All rights reserved.

Photos: Animal Tracks: July 11 - 18

loading photos...
  1. It's shark week somewhere

    A great white shark breaches while hunting its favorite food, the Cape fur seal. (Daren Fentiman / Zuma Press) Back to slideshow navigation
  2. Earning her stripes

    Wendy, the mother zebra of a newborn male, looks on at the Rome Zoo. (Alessandro Bianchi / Reuters) Back to slideshow navigation
  3. Fashion pet peeve

    A fashionable dog follows her owner on a street in Wenling, Zhejiang province of China. (Chinafotopress / Jiang Yongbing / Zuma Press) Back to slideshow navigation
  4. Chick magnet

    A South Korean specialist in distinguishing the sex of chicks separates males and females at a farm in Willgotheim in Eastern France. (Frederick Florin / AFP - Getty Images) Back to slideshow navigation
  5. How now, brown cow?

    A 2-month-old guernsey calf peeks out of the barn at Round Hill Park in Pennsylvania. (Rebecca Droke / Pittsburgh Post / Zuma Press) Back to slideshow navigation
  6. Under the sea?

    Girls are sillouetted as they watch a high definition movie shown at the Ginza Sony building in central Tokyo. (Toshifumi Kitamura / AFP - Getty Images) Back to slideshow navigation
  7. G'day!

    Lillian, a 6-month-old koala, is cradled between the front and back legs of her mother, Erna, at the zoo in Sydney. (Lorinda Taylor / AFP - Getty Images) Back to slideshow navigation
  8. Bee-utiful

    A bee lands on an exotic flower at the palace garden of Schloss Pillnitz castle in Pillnitz near Dresden, in eastern Germany. (Matthias Hiekel / AFP - Getty Images) Back to slideshow navigation
  9. Spidey senses

    People gather round a zebra tarantula spider on display at the Hong Kong International Reptile Expo. (Ed Jones / AFP - Getty Images) Back to slideshow navigation
  10. A fair shake

    Vitus, an 18-year-old male polar bear, shakes off water inside his enclosure at the zoo in Budapest. (Laszlo Balogh / Reuters) Back to slideshow navigation
  11. Surf's up

    Dolphins surf along a wave during day three of the Association of Surfing Professionals World Tour event in Jeffreys Bay, South Africa. (Nic Bothma / EPA) Back to slideshow navigation
  12. Make way for duckling

    A duckling makes its way through water lenses at the zoo in Berlin. (Tobias Kleinschmidt / AFP - Getty Images) Back to slideshow navigation
  13. Bubbly beluga

    A beluga, or white whale, exhales ring-shaped bubbles from its blowhole during its daily show at the Yokohama Hakkeijima Sea Paradise aquarium in suburban Tokyo. (Toru Yamanaka / AFP - Getty Images) Back to slideshow navigation
  14. Duck and cover

    Myanmar farmers drive a flock of ducks along a creek to a wetland in Bago, Myanmar. (Khin Maung Win / AP) Back to slideshow navigation
  15. That's deep

    A deep-sea anglerfish swims as scientists from the Queensland Brain Institute, using high-tech cameras, photographed sea creatures at a depth of over 1,000 meters at the Osprey Reef in the Coral Sea off the northeastern coast of Australia. (Justin Marshall / AFP - Getty Images) Back to slideshow navigation
  16. Waving hello

    A raccoon walks through his enclosure at the animal park in Springe near Hanover, western Germany. (Peter Steffen / AFP - Getty Images) Back to slideshow navigation
  17. Shear genius

    Two female shepherds catch an alpaca before shearing it near the Andean district of Larakeri in Peru. (Enrique Castro-Mendivil / Reuters) Back to slideshow navigation
  18. Island living

    A turtle travels on Easter Island. (Martin Bernetti / AFP - Getty Images) Back to slideshow navigation
  19. Caring cat

    Tita, a cat belonging to Ruben Gaviria, nurses a squirrel as her kitten plays with it at Gaviria's house in Envigado near Medellin in Colombia. (Albeiro Lopera / Reuters) Back to slideshow navigation
  20. All fur one, one fur all

    Two South African fur seals swim in a pool in their enclosure at a zoo in Frankfurt, Germany. (Boris Roessler / AFP - Getty Images) Back to slideshow navigation
  21. Pooped pooch

    A dog, Mochi, naps after being prepped for the "Patterns for Paws" charity dog fashion show, benefiting The Amanda Foundation, at the Pacific Design Center in West Hollywood. (Adam Lau / AP) Back to slideshow navigation
  1. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  2. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  3. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  4. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.


Discussion comments


Most active discussions

  1. votes comments
  2. votes comments
  3. votes comments
  4. votes comments