Pigeons don't come across as hierarchical animals, but a new study suggests that a few leaders set the direction for flocks. Modeling suggests this is the most effective way for large groups to navigate.
There are good reasons for flocks of pigeons to stay together: in particular, it reduces the chance of an individual being picked off by a predator. However, such teamwork requires some form of coordination, and some species do this better than others. There is a reason why we refer to “herding cats” and not “herding pigeons”.
In species such as elephants or gorillas it is obvious that alpha individuals are setting the direction of the group, but dominant pigeons don't make their presence known to humans in the same way. Nevertheless, researchers at Oxford University conclude that certain pigeons lead and others follow.
If birds knew exactly where they were going, coordination would not be required. However, despite their famous homing instinct, pigeons' perception of the direction home is not perfect. When left to their own devices, different birds will go in slightly different directions. Something needs to keep them together and allow them to decide which way to go.
“We've previously shown – through high-resolution GPS tracking of bird flocks – that homing pigeons have structured hierarchical relationships where individuals form stable leader–follower pairs during flight,” says author Dr Dora Biro.
The team modeled different coordination systems that match what the GPS observations revealed, using different settings for variables such as “attachment” between pairs of birds within the flock and “assertiveness,” which Biro describes as “the relative weight that each individual attached to its own information (where it thought the target was) .”
“Our results show that groups consisting of equally informed individuals achieve the highest level of accuracy when they are hierarchically organized with the minimum number of preferred connections per individual,” the authors report in Interface. “We also observe that the navigational accuracy of a group will depend strongly on detailed aspects of its social organization. More specifically, group navigation does not only depend on the underlying social relationships, but also on how much weight leading individuals put on following others.”
The models revealed that the more assertive individuals should position themselves in the center of the flock, where they can most easily influence other birds. While the researchers acknowledge that their models simplify the diversity of animal personality, they do closely match observations of the way pigeons bunch in flight and turn together.
“Perhaps most interestingly, we find that the presence of hierarchical social structure enables the group to both make decisions more accurately and to do so when the information it relies upon becomes worse,” says co-author Dr Robin Freeman of the Zoological Society of London.
The authors argue that other group species that rely on navigation for long migrations probably use similar techniques. How relevant the findings are to groups of humans was outside the scope of their investigation.