By following some simple rules, the patterns and behaviours seen in flocks of starlings can be described. Firstly, there is an element of short range repulsion which ensures collision avoidance. Secondly, attraction to the surrounding birds keeps the flock cohesive. The third rule is that each bird mimics the direction and speed of the birds around it.
By comparing these rules to the data, scientists found that each bird interacts with its closest 6 or 7 neighbours. This is far fewer than the number of birds it can see. The starlings have optimised how much information to take in. If the bird takes information from too many neighbours the data is too noisy. Its decision making is ill-informed. If the information is taken from too few neighbours, the information is too short-ranged.
Interestingly they found that this 6 or 7 number persists, regardless of the density of the flock. In fact, even sparse flocks keep their cohesion and because their visual range is so far any stragglers can quickly rejoin the flock.
[Interaction ruling animal collective behavior depends on topological rather than metric distance: Evidence from a field study - M. Ballerini, G Parisi et al 2008, PNAS]
Read more about my work on starling murmurations in my latest photo essay.
Cascade. The starlings appear to pour off the cables, as if they are a liquid.Fireworks. Anticipating how the flock would react was crucial to framing the action. Each image is the result of hundreds of hours of observation and filming the birds. Only on processing my footage did I find that I had captured a few intense moments where the birds of prey caused the starlings to scatter.Scribbles. Each bird mimics the flight path of its closest neighbours, creating repeating patterns within the flock.Untitled 1. The starlings assemble in communal roosts that range in size from a few thousand to over a million birds.Untitled 2. Battling strong winds, the birds fight to retain a cohesive form, creating loops, twists and spirals in the sky.Avalanche. Thousands of noisy chattering starlings gathered on the pylons as dusk approached, awaiting the critical moment the movement begins. The mass of individuals becomes self-organised and appears to move as one. The mathematics that describes the split second where thousands of individuals seem to act as a single entity is known as “criticality”. The very same science is behind how avalanches form.
Untitled 3. Shaped like the edge of a feather, starling flight paths reveal the order and cohesiveness of murmurations.Turbulence. The birds are tossed around by strong winds and driving rain and fight to stay within the safety of the group as they head toward the roost.Dementor; An evil and fearsome creature. The entire flock turns suddenly, the leading birds having spotted a peregrine falcon in their path. Creating such dramatic and foreboding patterns in the sky, it is little wonder that this natural phenomenon was once interpreted as messages from the spirit world.
