The aerial ballet that starlings perform while flocking is mesmerising
to watch. And the murmuration of this particular colony on the
limestone plateau around Gathabawn in North Kilkenny is a perfect
example of the world-wide phenomenon.
As starlings gather in the evenings to roost, often they will
participate in a huge flock that shape-shifts in the sky as if it were
one swirling liquid mass.
In this instance we are indebted to Mary Durkin for sending us in the
video and to Ian McCullagh for capturing the footage.
It seems, the behaviour is sparked by the presence of a hawk and the
flock's movement is based on evasive manoeuvres. There is safety in
numbers, so the individual starlings do not scatter, but rather are
able to move as an intelligent cloud, feinting away from a diving
raptor, thousands of birds changing direction almost simultaneously.
The question that has had scientists stumped is how a bird, tens or
hundreds of birds away from those nearest danger, sense the shift and
move in unison?
According to the website, earthmatters.com the secret lies in the same
systems that apply to anything on the cusp of a shift, like snow
before an avalanche, where the velocity of one bird affects the
velocity of the rest. It is called "scale-free correlation" and every
shift of the murmuration is called a critical transition.
Parisi, a theoretical physicist with the University of Rome, lead a
research team looking into the amazing movement of starlings and
published a paper in the Proceedings of the National Academy of
"The change in the behavioural state of one animal affects and is
affected by that of all other animals in the group, no matter how
large the group is. Scale-free correlations provide each animal with
an effective perception range much larger than the direct
inter-individual interaction range, thus enhancing global response to
Because the size of the flock doesn't matter, a huge flock is able to
respond to a predator attack as effectively and fluidly as a small
flock. No matter the size, the system works. If one bird changes speed
or direction, so do others. The question remains, however, how does an
individual bird spark a change if all are busy responding to the
movement of everyone else? And more importantly, how do they do it so
"In particle physics, synchronised orientation is found in systems
with 'low noise,' in which signals are transmitted without degrading.
But low noise isn’t enough to produce synchronised 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," writes Wired.
The team's research suggests that starling murmurations are just such
a critical system.
In 2012, the team published further research showing that each bird is
actually reacting to the birds nearest to it, that the movement is the
result of a series of short-range reactions. With the 2010 study the
team looked at velocity; this time they studied orientation. Measuring
how a change in direction by one bird affects those around it, the
team discovered that one bird's movement only affects its seven
closest neighbours. So one bird affects its seven closest neighbours,
and each of those neighbors' movements affect their closest seven
neighbours and on through the flock. This is how a flock is able to
look like a twisting, morphing cloud with some parts moving in one
direction at one speed and other parts moving at another direction and
at another speed.
"The closest statistical fit for this behaviour comes from the physics
of magnetism, and describes how the electron spins of particles align
with their neighbours as metals become magnetised," reports Wired. "In
future research, Giardina’s team plans to study flocking in other
organisms, such as local species of midges, which demonstrate other
patterns of collective flight."
Why seven? It's one of those numbers that just works in nature, and a
systems-theoretic approach to studying starling flocks showed it.
"Interacting with six or seven neighbours optimises the balance
between group cohesiveness and individual effort," write the
But even more fascinating is the science behind how they are capable
of such coordinated movement.
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