It is always amazing to watch birds in flight because they often behave as if they respond to unseen commands when they turn in unison. Pigeons have been recently studied by Oxford University and Eötvös University (Hungary) to see who is command in a given flock. Pigeon flocks (they concluded) are guided by a flexible system of leadership in which almost every member gets a vote but the votes of high ranking birds seem to carry more weight.
Pigeons are a member of the bird family Columbidae (doves and pigeons). Pigeons are commonly seen in many major cities and have been raised as pets or used as carrier pigeons for their homing ability.
Scientists used GPS (Global Positioning System) backpacks to record the flight paths of individual pigeons and then analyzed their interactions with each other. Their findings could help us understand the collective behavior of other animals, including humans
"We are all aware of the amazing aerobatics performed by flocks of birds but how such flocks decide where to go and whether decisions are made by a dominant leader or by the group as a whole has always been a mystery," said Dr Dora Biro of Oxford University’s Department of Zoology, an author of the paper. "We found that, whilst most birds have a say in decision making, a flexible system of rank ensures that some birds are more likely to lead and others to follow."
The miniature GPS loggers weighing just 16 grams were fitted into custom made backpacks carried by flocks of up to 10 homing pigeons. These enabled scientists to explore spatial and temporal relationships between individual birds and the movement decisions they made at the scale of a fraction of a second.
The team measured shifts in the flight direction of each bird every 0.2 seconds and tried to line up these changes across different birds in the flock to determine who initiated any given change in direction and who followed (and with what time delay). The research revealed unexpectedly well defined hierarchies within the flocks, with a spectrum of different levels of leadership.
A hierarchy is the organization of individuals in a group often in response to a threat or competition/aggression. Schjelderup-Ebbe, who studied the often cited example of the pecking order in chickens (a dominance based hierarchy), found that such social structures lead to more stable flocks with reduced aggression among individuals.
Dominance hierarchies can be despotic or linear. In a despotic hierarchy, only one individual is dominant, while the others are all equally submissive. In a linear hierarchy, for example, in the above cited pecking order of chickens, each individual dominates all individuals below him and not those above him.
Dominance hierarchies occur in most social animal species, including primates who normally live in groups. Dominance hierarchies have been extensively studied in fish, birds, and mammals. Dominance hierarchies can be simple linear structures, which often arise from the physical differences among individuals in a group in relation to their access to resources. They are also influenced by the complex social interactions among individuals in the group.
The type of hierarchy amongst pigeons is still to be determined. The current study suggests that the pigeon hierarchy is flexible yet predictable. Any given pigeon may be in a position to respond and lead the flock or lend a "vote" to the overall decision. How such a leader is selected or a consensus is reached is not known.
The team also discovered that a bird’s position in the flock matched its position in the hierarchy, with individuals nearer the front more likely to be responsible for decisions. Additionally, they found that followers responded more quickly to those flying on their left, confirming observations in the laboratory that suggest birds process information predominantly through input that the brain receives from the left eye.
The researchers believe their findings could help unravel the decision making process in many other groups of animals. Further studies may reveal how such a sophisticated leadership strategy confers evolutionary advantage on individuals over a strategy based on a single leader or one in which all members contribute equally to decision making.
A report of the research, entitled "Hierarchical group dynamics in pigeon flocks", was published in Nature on April 8.
For further information: http://www.ox.ac.uk/media/news_stories/2010/100408_1.html