[THS] Starling flocks fly like a single entity (w/ Video)

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Starling flocks fly like a single entity 
(w/ Video at www.physorg.com/news195976212.html )

June 17th, 2010 in Physics / General Physics
Flock of birdsFlock of birds. Image: Wikipedia.

(PhysOrg.com) -- An animal group such as a school of fish or a flock of starlings can
seem like a single entity governed by a collective mind. A new mathematical analysis
of flight dynamics in flocks of starlings suggest this is because the birds are effectively
a single network, with every bird’s movements affected by every other bird’s
movements, as if they were all connected together.

The phenomenon adopted by the flock of starlings (Sturnus vulgaris) is called “scale-
free behavioral correlation,” which occurs outside of biology in events such as an
avalanche or the formation of crystals, both of which are critical systems in which
nearly instantaneous transformation can occur.

When a starling flock acts as if it were a single entity it is acting as a critical system
and is also optimizing its collective response to challenges such as a predator attack,
according to theoretical physicist Giorgio Parisi and colleagues from the University of
Rome. who carried out the study.

The researchers studied flocks of starlings over a major winter roosting site in Rome,
measuring the 3D positions and velocities of individual birds. The flocks of birds spent
their days in the countryside and returned to the city before sunset, performing aerial
displays before they settled for the night. The displays appeared like an aerial dance
in which the flocks moved and swirled together. The researchers used stereometric
digital photogrammetry and computer vision techniques to reconstruct the 3D
positions and 3D velocities of the individual birds in the flock from the consecutive
shots of the flock, which were taken at 10 frames per second.

Starling flocks fly like a single entity(A) The 2D projection of the velocities of the
individual birds within a starling flock. (B) This is the 2D projection of the individual
velocity fluctuations in the same flock at the same instant of time as in A (vectors
scaled for clarity). Large domains of strongly correlated birds are clearly visible.
The flocks ranged in size from 122 birds to 4,268, but the size of the flock made no
difference to the way they moved. In every case if any one bird turned and changed
speed, so did every other bird. What was most surprising to the scientists was the
near-instantaneous signal processing speed. How the birds achieve this feat is a
mystery.

The synchronization of speeds and orientation is found in critical systems. An example
cited by the researchers is ferromagnetism, in which particles in a magnet display
perfect interconnection at a specific “critical” temperature.

Physicist Irene Giardina, one of the study’s co-authors, said the results suggest
starling flocks behave as critical systems “poised to respond maximally to
environmental perturbations,” but she said more analysis would be needed to prove
this definitively.

/Andrea Cavagna
The behavior of the flock of starlings is different to the behavior of a group following
a leader. Such a group would move in the same direction and would appear strongly
ordered, but there would be no passing of information between individuals and so
behavioral fluctuations are independent, with changes in direction of an animal other
than the leader having little effect on other members of the group. The starlings’
behavior is an example of self-organization, and the collective response to events
such as attack by predators gives them a distinct advantage.

The paper is available online from the Proceedings of the National Academy of
Sciences (PNAS).

More information: Andrea Cavagna et al., Scale-free correlations in starling flocks,
Proceedings of the National Academy of Sciences, Published online before print June
14, 2010, doi:10.1073/pnas.1005766107

© 2010 PhysOrg.com

"Starling flocks fly like a single entity (w/ Video)." June 17th, 2010.
www.physorg.com/news195976212.html