Amazing Starling Flocks Are Flying Avalanches
To watch the uncanny synchronization of a starling flock in flight is to wonder if the birds aren’t actually a single entity, governed by something beyond the usual rules of biology. New research suggests that’s true.
Mathematical analysis of flock dynamics show how each starling’s movement is influenced by every other starling, and vice versa. It doesn’t matter how large a flock is, or if two birds are on opposite sides. It’s as if every individual is connected to the same network.
That phenomenon is known as scale-free correlation, and transcends biology. The closest fit to equations describing starling flock patterns come from the literature of “criticality,” of crystal formation and avalanches — systems poised on the brink, capable of near-instantaneous transformation.
In starlings, “being critical is a way for the system to be always ready to optimally respond to an external perturbation, such as predator attack,” wrote researchers led by University of Rome theoretical physicist Giorgio Parisi in a June 14 Proceedings of the National Academy of Sciences paper.
Parisi’s team recorded starling flocks on the outskirts of Rome. Some had just over 100 birds, and others more than 4,000. Regardless of size, the correlations of a bird’s orientation and velocity with the other birds’ orientation and velocity didn’t vary. If any one bird turned and changed speed, so would all the others.
In particle physics, synchronized orientation is found in systems with “low noise,” in which signals are transmitted without degrading. But low noise isn’t enough to produce synchronized speeds, which are found in critical systems. The researchers give the example of ferromagnetism, where particles in a magnet exhibit perfect interconnection at a precise, “critical” temperature.
“More analysis is necessary to prove this definitively, but our results suggest” that starling flocks are a critical system, said study co-author Irene Giardina, also a University of Rome physicist.
According to the researchers, the “most surprising and exotic feature” of the flocks was their near-instantaneous signal-processing speed. “How starlings achieve such a strong correlation remains a mystery to us,” they wrote.