The road home
Confucius taught elected leaders of the people how to govern the country virtuously. A fundamental principle was: to be strict with yourself and lenient with others. But also, if the people became dissatisfied, they should immediately step down.
In animal groups where specific individuals disproportionately influence collective decisions, the whole group’s performance may suffer if these individuals have incorrect information. Whether leaders in such situations can be replaced in their roles by better-informed group mates is an essential question in understanding the adaptive consequences of collective decision-making.
With pigeons, they used a time-shifting procedure (from an artificially set day-night clock) to manipulate the predictability of directional error in navigational information from established leaders within the swarm hierarchy of carrier pigeons (Columba livia).
The shifting of the clock places the solar compass, an important navigation signal, in conflict with all other directional signs (e.g. visual, magnetic) in the pigeon's vicinity.
Experimental and leadership analysis (a)
Clearance protocol for the eight experimental pairs (b, c)
The trial reveals that
- in most cases, when leaders have incorrect information, they lose their influence over the swarm. In these cases, inaccurate information is filtered out by rearranging hierarchical positions, preventing mistakes made by former leaders in the hierarchy.
- A flexible decision-shaping mechanism can be valuable when traditionally influential individuals introduce 'bad' information.
Theoretically, it was predicted that in hierarchical decision-making, leader errors propagate downwards, resulting in inaccurate collective decisions. By introducing incorrect navigation information of a specific size at the top of the hierarchy, it was found that this disadvantage could be overcome in pigeon swarms: when leaders alone were poorly informed, swarms retained their existing routes, while if when whole swarms were misled (by shifting light clock), they showed divergent paths, albeit with a more minor than predicted deviation, as to be expected in pigeons familiar with the landscape.
So we can deduce that deception by shifting the (light) clock was successful, but leaders alone were unable to 'mislead' their swarms to the wrong routes.
Also significant is the decrease in leaders’ hierarchical ranks: in most swarms, their input in navigational decisions diminished when only their light clock was shifted. It is assumed that where a decline was observed in the hierarchical rank of leaders, this could be due to two non-exclusive mechanisms.
First, shifting the day/night clock may have made leaders uncertain about the quality of their information. Turning the clock places the solar compass, an important navigation signal, in conflict with all other directional cues (e.g. visual, magnetic) in the pigeon's environment. This conflict may have driven leaders to place less weight on their personal information and more on social information (i.e. copying that of peer groups). Uncertainty may also have reduced the flight speed of the (clock-shifted) leader, and because speed is associated with leadership in pigeons, a slower flight may cause pigeons to fall down the hierarchy.
This mechanism requires no recognition by followers that their leader has incorrect information. Alternatively, swarm members may actively have 'filtered out' low-quality information by reducing their reliance on social information from leaders. This may be due to recognising the increased conflict between their directional preference and that of the leader or detecting a clue (such as reduced speed) indicating uncertainty in the leader. The latter mechanism thus corresponds to followers who choose not to follow and the former to leaders who choose not to lead. At present, we cannot differentiate between these alternatives.
This study revealed that flexible decision-making structures could be valuable when information can be introduced with many errors by influential individuals. These results have implications for theoretical and experimental collective movement and navigation studies. They emphasise the importance of the quality of information and individual security of interactions between pigeons during swimming flights.
The loss of swarm-flying pigeons due to navigational errors under weak leadership is subject to "swarm compensation".
The numerous theories of how they navigate must now be viewed differently. It is best to take the expression "dumb pigeons" with a pinch of salt because they are masterful problem solvers.
We learn that pigeons also react (fly slower) when they become uncertain about their information. They fly cautiously and slower because they want to check the information on multiple navigational techniques. Just like humans, when they are no longer confident on the road, they will also drive slower. Before they are finally flying home alone in a race flight, frequent swarm splits appear, with a new leader taking the lead each time until the swarm consists of only three pigeons. In these splits, a pigeon from the group whose clock has not been moved (has correct information) will always take over as the better leader.
These measurements can help us interpret both individual stragglers and traumatising disaster flights…